Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

  • Socioecological predictors of immunity in wild spotted hyenas Flies et al
  • Ecological equivalence of species within phytoplankton functional groups  Mutshinda et al
  • South for the winter? Foraging effort and divergent strategies in fur seals Arthur et al
  • Direct and indirect effects of shrub encroachment on alpine grasslands mediated by plant-flower-visitor interactions Lara-Romero et al
  • Genes that influence salmon growth in wild don’t matter in captivity Vasemägi et al
  • How do metabolic rate and food-deprivation affect sociability in fish? Killen et al
  • Both spreading and non-spreading exotic plants receive sufficient pollination Razanajatovo and Kleunen
  • Wildlife mobility and extinction risk in human-altered landscapes Martin and Fahrig
  • Parental age influences offspring telomere loss Heidinger et al
  • Ecological relevance of cellular energy metabolism in intertidal species Dong & Zhang
  • Top-down becomes bottom-up: consequences of nutrient cycling for trophic cascades between green and brown webs Zou et al
  • Reseeders benefit from arid climates and infertile soils Wüest et al
  • How do soil respiration components and their specific respiration change with forest succession? Huang et al
  • To sprout, or not to sprout: freezing temperature drives spring flushing Lenz et al
  • Survival benefits of winter dormancy: warmer climates are associated with shorter hibernation seasons and reduced survival in rodents Turbill and Prior
  • Which is more important: direct environmental effects, or local adaptation, in determining how many times animals reproduce? Schwarzkopf et al
  • Temperature-dependence of fish performance in the wild: links with species biogeography and physiological thermal tolerance Payne et al
  • Decoupled root and leaf decomposition in trees Ma et al
  • When does clumping help insects escape parasitism? Gunton & Pöyry
  • Individual decision-making by prey may affect the strength of food chains Gravem and Morgan
  • Functional strategy composition is a good indicator of species dynamics Török et al
  • Do invaders most strongly impact similar species? Case et al
  • Tree resprouting and carbo hydrate allocation Shibata et al
  • Silicon in aquatic vegetation Schoelynck & Struyf
  • City slickers: poor performance does not deter Anolis lizards from using artificial substrates in human-modified habitats Kolbe et al
  • Coexistence resulting from being more different or more similar? Zhao et al
  • Soil microbial communities matter for carbon cycling during drought Orwin et al
  • Evolution in space: metapopulation structure and life history evolution De Roissart et al
  • Heat hardening in a tropical lizard: geographic variation explained by the predictability and variance in environmental temperatures Phillips et al
  • Oxidative stress changes how birds make decisions Costantini et al
  • Air humidity thresholds trigger active moss spore release to extend dispersal in space and time Johansson et al
  • Transgenerational plasticity and environmental stress: do paternal effects act as a conduit or a buffer? Guillaume et al
  • Experimental effects of early-life corticosterone on the HPA axis and pre-migratory behaviour in a wild songbird Pakkala et al
  • The importance of biotic interactions for the prediction of macroinvertebrate communities under multiple stressors Schuwirth et al
  • Diet determines movement rates and size of area used for herbivores Tablado et al
  • Impacts of toxic nectar on three pollinators Tiedeken et al
  • Energy expenditure at rest affects reproduction and survival in house sparrows Rønning et al
  • Short-term rainfall, not temperature, controls lizard microhabitat use in a piñon-juniper woodland Ryan et al
  • Friend or foe? Lessons from cushion alpine plants and their neighbours Bonanomi et al
  • Agricultural stressors affect stream ecosystems in unexpected ways Bruder et al
  • Biotic and abiotic interactions, but not plant chemistry alone, contribute to chemical identity of invaded soils Suseela et al
  • Predation, food, and male-male competition drive natural variation in lizard tail autotomy Kuo and Irschick
  • Do non-native plants have the same traits at home? A comparison in France and New York Heberling et al
  • Comparing the decomposition of plant litter in aquatic and terrestrial ecosystems García-Palacios et al
  • Cold hardiness does not limit range shifts of Mediterranean pines to Central and Western Europe Bachofen et al
  • Additive genetic variance and effects of inbreeding, sex and age on heterophil to lymphocyte ratio in song sparrows Losdat et al
  • Fewer new species colonize at low frequency N addition in a temperate grassland Zhang et al
  • Environmental cue to germinate in gaps is closely associated with seed sizes Xia et al
  • Dung beetles reduce drought stress in plants without increasing plant susceptibility to an aboveground herbivore Johnson et al
  • Seasonal changes in temperature and bush lupine availability drive bordered plant bug abundance Johnson et al
  • Liverworts to the rescue: an investigation of their efficacy as mycorrhizal inoculum for vascular plants Kowal et al
  • Old birds become worn and rusty too Herborn et al
  • Functional replacement across species pools of vertebrate scavengers separated at a continental scale maintains an ecosystem function Huijbers et al
  • Re-growing a tropical dry forest: functional plant trait composition and community assembly during succession Buzzard et al
  • Visual ecology of Eulemur suggests a cathemeral origin for the primate cone opsin polymorphism Valenta et al
  • Food as fuel: How food protein-carbohydrate content affects resting metabolic rates Clark et al
  • Trade-offs in juvenile growth potential vs. shade tolerance among subtropical rainforest trees on soils of contrasting fertility Sendall et al
  • Colour pattern mimicry in flowers- the functional importance of complex floral colour pattern in a food-deceptive orchid Ma et al
  • Molecular evolution of aquaporins and silicon influx in plants Deshmukh and Bélanger
  • How do precipitation gradient and evolutionary history shape the variations in leaf and root traits in the Inner Mongolia grassland? Cheng et al
  • Cold adaptation in insects involves adaptive modifications of the cell membrane phospholipid composition Slotsbo et al
  • Macronutrients, weapons and genital traits in male broad horned beetles House et al
  • Why baby birds differ in the speed at which they grow? Ton & Martin
  • Effects of neonatal size on maturity and escape performance in the Trinidadian guppy Dial et al
  • Wood decomposition inside living trees shows that hollows develop slowly but cause a considerable loss of forest biomass Zheng et al
  • Black and yellow plumage signals resistance to oxidative stress in a bird Henschen et al
  • Individual-level trait diversity indices Fontana et al
  • Water use by Swedish boreal forests in a changing climate Hasper et al
  • Nitrogen deposition affects Scots pine stoichiometry Sardans et al
  • Unseen consequences of losing large wildlife: increases in rodent immune function following large mammal defaunation Young et al
  • The Importance of Agriculture in Global Biogenic Silicon Production Carey & Fulweiler
  • Facilitation among plants as an insurance policy for diversity in Alpine communities Cavieres et al
  • Flowers avoiding bees? The case of Costus arabicus colour variation sheds light on bee sensorial exclusion hypothesis for hummingbird red-flowers Bergamo et al
  • Multiple environmental drivers structure plant traits at the community level in a pyrogenic ecosystem Ames et al
  • Frog habitat preferences do not maximize jumping performance Mitchell & Bergmann
  • Tracking woodland water use efficiency under future atmospheric conditions Gimeno et al
  • Breath of death: how a parasite favours its transmission through hijacking its host’s hypoxia-acclimation processes Perrot-Minnot et al
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    Socioecological predictors of immunity in wild spotted hyenas

    Andrew S. Flies, Linda S. Mansfield, Emily J. Flies, Chris K. Grant, and Kay E. Holekamp Spotted hyena (Crocuta crocuta) feeding on the carcass of a giraffe that has been dead for three days. Photo by Andrew S. Flies.

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    The immune system is critically important for survival and any breakdown of immune defenses could result in death. Most of what we know about the vertebrate immune system has been acquired by performing experiments on animals whose diet, pathogen exposure and social interactions are all tightly controlled. However, wild animals must compete for food and mates, produce offspring, avoid being killed by predators, and respond to a broad range of diseases over the course of their lifetime.

    In this study we examine the effects of sex, social rank, and reproductive status on immune defenses in spotted hyenas (Crocuta crocuta) that can live for more than 20 years in the wild and are routinely exposed to a plethora of pathogens, including rabies and anthrax, yet rarely show signs of disease. Here we show that high-ranking spotted hyenas have stronger immune defenses than low-ranking hyenas. Additionally, females have stronger immune defenses than males, which is similar to the pattern observed in most other mammals. Interestingly, female hyenas are (unusually for mammals) larger and socially dominant to male hyenas, so we had suspected that the size and dominance reversals might also lead to a reversal of immune defense levels, but this was not the case.

    We also found that immune defenses are lower in females when they are lactating than when they are pregnant. Producing milk for offspring actually uses more energy than producing the offspring in the first place, so this suggests that lactating females spend so much energy producing milk that they cannot spare extra energy for immune defenses. Our observations that high-ranking hyenas have stronger immune defenses than low-ranking hyenas also suggests that activating the immune system uses large amounts of energy, because high-ranking hyenas get more high-quality food than low-ranking hyenas and thus can devote more energy resources to immune function.

    Altogether these studies shows that sex, social rank, and reproductive status are important for immune defenses. This information can help us predict how pathogens will impact wild animals at the individual and population levels and may lead to new insights into the relationship between socioeconomic status and disease in humans.

    Image caption: Spotted hyena (Crocuta crocuta) feeding on the carcass of a giraffe that has been dead for three days. Photo by Andrew S. Flies.
    You can read the article in full here.

     

    Ecological equivalence of species within phytoplankton functional groups

    Crispin M Mutshinda, Zoe V Finkel, Claire E. Widdicombe, Andrew J IrwinDitylum brightwellii is one of many diatom species observed at Station L4 in the Western English Channel.

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    Phytoplankton are a very diverse set of microscopic photosynthetic organisms that live in the upper sun-lit region of the water column. They account for about half of all photosynthesis on Earth. Anthropogenic climate change is expected to change phytoplankton biogeography and productivity through changes in temperature, resource availability, and ocean physics. Climate models that aim to predict changes in phytoplankton productivity usually approximate the tremendous diversity of phytoplankton by a very small number of functional groups, but the validity of this approximation is rarely tested. Two contrasting views of the dynamics of individual species’ biomass are that variability is driven primarily by changes in the environment and interactions among species (called niche selection) or alternatively that variability is largely random and all species are ecologically equivalent (called the neutral model).

    Here we develop models to describe the variation in biomass of two major functional groups (diatoms, dinoflagellates) observed at a time-series station in the Western English Channel and show that the functional groups are strongly affected by niche selection. We then test if the biomass of individual species relative to the total biomass of the corresponding functional group varies neutrally or if there is evidence that individual species are further selected by environmental or other factors. We show that phytoplankton species vary neutrally within their functional group, which supports the approach of aggregating many species into broad functional groups for modeling purposes.

    Image caption: Ditylum brightwellii is one of many diatom species observed at Station L4 in the Western English Channel.
    You can read the article in full here.

     

    South for the winter? Foraging effort and divergent strategies in fur seals

    Benjamin Arthur, Mark Hindell, Marthan N. Bester, W. Chris Oosthuizen, Mia Wege and Mary-Anne LeaFemale Antarctic fur seal with geo-location tag (flipper) and time-depth recorder (back). Credit Chris Oosthuizen.

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    Obtaining food is a problem that is faced by all animals. As a result, a diverse array of foraging strategies has evolved to acquire food resources. Understanding these strategies, and the choices made by foraging animals, is a fundamental aim in animal ecology. Air-breathing divers, such as seals, are a unique case when examining foraging choices, as individuals must forage throughout both horizontal and vertical space within the limits of oxygen availability. Being able to measure foraging effort within dives can reveal not only how animals use their environment, but the energetic trade-offs associated with different foraging strategies, particularly when combined with additional information on location, dive depth and dive duration.

    Using a novel within-dive approach, we quantified the foraging effort of 12 female Antarctic fur seals across a wide geographic area in the Southern Ocean during their post-breeding winter migrations. We identified two main contrasting foraging strategies. Seals that stayed closer to the colony and remained North of the Polar Front (a prominent oceanographic feature) had relatively long and deep dives and an increased foraging effort. On the other hand, seals that travelled South of the Polar Front had relatively short and shallow dives with a reduced foraging effort. As the prey of fur seals is closer to the surface at night and therefore more easily accessed, the longer night duration further south at this time of year also meant that these seals had more available foraging time each day. However, seals foraging in this region also have to balance the energetic cost of travelling to such remote areas.

    The fact that these two contrasting foraging strategies seemingly co-exist within the population indicates that neither currently offers a significant long-term energetic advantage over the other. However, our results raise questions about the viability of these strategies over the long term, particularly with potential future changes to population size and environmental conditions.

    Image caption: Female Antarctic fur seal with geo-location tag (flipper) and time-depth recorder (back). Credit Chris Oosthuizen.
    You can read the article in full here.

     

    Direct and indirect effects of shrub encroachment on alpine grasslands mediated by plant-flower-visitor interactions

    Carlos Lara-Romero, Cristina García, Javier Morente-López and José M. IriondoImage provided by authors.

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    Rural abandonment is widespread across anthropic landscapes and, in combination with global warming, has elicited profound shifts in the composition of plant communities. These changes in vegetation have cascading effects on many organisms that interact with plants, such as microorganisms or pollinators. As a result, ecosystem services provided by these ecosystems, such as pollination services, may be extensively altered.

    Alpine grasslands have been reported to undergo rapid shrub encroachment in recent decades mainly as a result of rapid land-use changes. This is expected to impact the population dynamics of native herbs by modifying the type and strength of their mutualistic interactions, such as the pollinator services that are crucial to seed production. Yet we lack a robust quantification of the effect of shrub encroachment in modifying plant-pollinator interaction networks between native alpine herbs and their floral visitors (as a proxy for pollinators).

    The Functional Biodiversity Hypothesis (FBH) states that higher diversity of functionally complementary plants (the producer trophic level) contributes to better meeting of pollinator requirements (the consumer trophic level). This in turn results in increased diversity of specialist pollinators and improved plant performance (via increased pollinator services provided by specialist pollinators). In order to evaluate the effect of shrub encroachment in alpine grasslands we tested the FBH by applying network theory that accounts for both trophic levels simultaneously. We compared several structural metrics of two plant-floral visitor networks collected in two alpine grasslands, one of them undergoing a moderate level of shrub encroachment.

    Encroached grasslands harboured a more diverse community of both herbaceous flowering plants and floral visitors than non-encroached ones, thus supporting the FBH. Moderate levels of shrub encroachment increased the number of pollen visitors per plant, but it also intensified indirect plant-plant competition for shared pollinators, which can result in reduced reproductive success of key native wildflowers. From an applied perspective, our results show how changes in community function can be efficiently tracked using metrics of plant- and flower-visitor networks.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Genes that influence salmon growth in wild don’t matter in captivity

    Anti Vasemägi, Siim Kahar and Mikhail Yu. OzerovPhoto provided by authors.

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    Understanding how and what genes affect ecologically important traits provides the important first step towards understanding the targets of natural selection and adaptation processes in the wild. Typically, identification of the genomic regions influencing various traits, such as growth, coloration or behaviour has been performed in controlled laboratory conditions, and it is often assumed that genes have similar effects both in the laboratory and in nature. However, the environment may strongly influence the impact of genes.

    Atlantic salmon is one of the major aquaculture species and a popular target for various restoration and supplementary stocking programs, in which the species is bred and reared in a hatchery for subsequent release into the natural environment. Both selective breeding and inadvertent selection have increased farmed salmon growth rate, and earlier studies have identified a large number of genomic regions that influence growth of salmon in fish farms. However, no studies exist that have compared if the genes that affect growth in farmed conditions have similar effects in the wild.

    In this study, we identified several genomic regions that influence the size of juvenile salmon only in either hatchery or natural conditions. Our results indicate that the growth of juvenile salmon is controlled by different genetic mechanisms in the two environments. We suggest that genes affecting growth of juvenile fish in fish farms are more likely driven by competition for food, aggression and energy balance; whereas genes that affect growth in the wild may be linked to other factors such as individual movement and anti-predator behavior. Our findings also imply that a substantial proportion of the genomic regions associated with growth in salmon may be specific to farmed conditions and hence, have no effect on fish growth in the wild. Our work demonstrates the benefits of studying the effects of genes in multiple environments and in a realistic ecological context.

    Image caption: Photo provided by authors.
    You can read the article in full here.

     

    How do metabolic rate and food-deprivation affect sociability in fish?

    Shaun S. Killen, Cheng Fu, Qingyi Wu, Yu-Xiang Wang and Shi-Jian FuImage provided by authors.

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    Many animal species spend at least part of their time living in groups. With many eyes searching, group membership can allow animals to consistently find food. A potential drawback is that some group members can take more than their fair share of found food. Animals must weigh these benefits and costs when determining how closely they will associate with groups.

    A number of factors might affect an animal’s level of sociability. Previous studies in fish have shown that a few days of fasting can cause individuals to stray from groups to decrease competition for food. In the same way, individuals with a higher metabolic rate could be less social to maximise food intake to satisfy their heightened energy demand. Unknown is how prolonged food-deprivation affects sociability. It is very common for wild fishes to experience weeks of food-deprivation during seasonal changes in food availability. The effects of longer-term food deprivation on sociability could differ drastically from the effects of shorter-term hunger.

    We examined these issues in juvenile qingbo carp Spinibarbus sinensis. In the laboratory, individuals were either food-deprived for 21 days (to simulate a bout of seasonal food-deprivation), or fed a maintenance ration. Fish from each diet treatment were measured for metabolic rate and tested for sociability twice: once in the presence of a well-fed control shoal of fish and once with a food-deprived shoal.

    Over the course of a 30 minute trial, fish that had been on a maintenance ration ventured further away from shoals, while food-deprived fish remained close to the shoal. This is unlike fish that have been fasted for a few days, which tend to decrease association with shoals. Prolonged food-deprivation may cause individuals to put such a high priority on food-acquisition that they need to remain with their group to help alert them to predators while they continuously forage.

    Among well-fed fish, those with a higher metabolic rate were least sociable, especially when exposed to food-deprived shoals. This probably minimises competition, allowing them to satisfy an increased energetic demand while foraging. Overall, these results suggest that energy demand and food-deprivation – a challenge common for many ectothermic species – can affect individual sociability as well as the attractiveness of groups to members of their species.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Both spreading and non-spreading exotic plants receive sufficient pollination

    Mialy Razanajatovo and Mark van Kleunen Pimpinella peregrina, a non-spreading exotic plant, visited by a syrphid fly in our research garden. Photo credit: Samuel Carleial.

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    As a result of introduction by humans, many plant species manage to maintain reproducing populations without further human intervention in regions where they did not naturally occur. Some of these exotic species spread in the new regions, and can cause serious environmental and economic damage. Therefore, what drives species invasions is a major question in ecology.

    The ability to reproduce in the new regions determines, at least partly, whether or not exotic species can found and maintain populations. As exotic plants are decoupled from their usual pollinators, not all of them might find suitable pollinators. Exotic plants that can reproduce in the absence of pollinators and those capable of attracting suitable pollinators should therefore have an advantage over the ones that lack these capacities, as the latter might not receive sufficient pollination.

    Using a common garden experiment, we compared pollination characteristics of eight native and 16 exotic plant species in Germany. We included eight widespread exotic species and eight rare ones. For each species, we assessed the degree to which fruit and seed production deviate from that expected under sufficient pollination. We also assessed fruit and seed production capacities when pollinators are excluded.

    In all three plant groups (native, widespread exotic and rare exotic species), fruit and seed production did not significantly deviate from that expected under sufficient pollination, and this did not significantly differ among groups. Species in all three plant groups were, to some extent, capable of fruit and seed production when pollinators were excluded, and this also did not differ among groups. Our results thus suggest that all three plant groups receive sufficient pollination, at least in our common garden.

    Plant species that do not receive sufficient pollination might not be able to found populations. Later in the invasion process, however, when the exotic species spread in the landscape, other factors that we did not investigate in our study might play a more important role.

    Image caption: Pimpinella peregrina, a non-spreading exotic plant, visited by a syrphid fly in our research garden. Photo credit: Samuel Carleial.
    You can read the article in full here.

     

    Wildlife mobility and extinction risk in human-altered landscapes

    Amanda E. Martin and Lenore FahrigAn aerial view of New York City, New York, USA, as an example of a human-altered landscape. Photo courtesy of Jason C. Newland.

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    It is widely thought that a species’ mobility affects its extinction risk in a human-altered landscape; however, some studies suggest that mobile species are less at-risk than sedentary species, while others suggest the opposite. In this study we asked: Why do studies find different effects of species mobility on extinction risk? We used a computer model to address this question, so that we could investigate a number of possible explanations, and identify which explanations are most likely and should therefore be investigated empirically.

    Our results supported two explanations for the contradictory findings on the role of mobility in extinction risk. First, that the mobility-risk relationship depends on how you measure mobility: extinction risk increased with mobility when mobility was measured as emigration, i.e. the tendency of individuals to leave their home range or territory, but decreased when mobility was measured as immigration, i.e. successful movement between populations. This is likely because emigration reflects the cost of dispersal, i.e. risk of mortality when moving through human-dominated areas, while immigration reflects the benefits of dispersal, i.e. ability to recolonize unused habitat and rescue small populations that might otherwise go extinct. Second, our results suggest that the mobility-risk relationship depends on the attributes of the landscapes in which the studied species evolved. Species in landscapes with historically abundant, un-fragmented habitat and frequent disturbance had greater risk and mobility than species in landscapes with historically rare, fragmented habitat and infrequent disturbance: for these species, risk was higher for more mobile species. However, species in landscapes with high-risk matrix (i.e. non-habitat areas in the landscape) had greater risk but lower mobility than species with low-risk matrix; for these species, risk was lower for more mobile species.

    To our knowledge, this is the first study to investigate why some studies find that more mobile species are less at-risk, while others find the opposite. Understanding what influences extinction risk can help us identify species of conservation concern. Our results suggest that we should focus on species with high emigration rates but low immigration rates, and those that evolved in landscapes with non-fragmented habitat and high-risk matrix.

    Image caption: An aerial view of New York City, New York, USA, as an example of a human-altered landscape. Photo courtesy of Jason C. Newland.
    You can read the article in full here.

     

    Parental age influences offspring telomere loss

    Britt J. Heidinger, Katherine A. Herborn, Hanna M.V. Granroth-Wilding, Winnie Boner, Sarah Burthe, Mark Newell, Sarah Wanless, Francis Daunt and Pat MonaghanIncubating shag. Photo provided by Mark Newell.

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    Older parents are known to produce offspring that tend to show reduced longevity. However, currently we do not know much about the processes responsible for this effect. One contributory factor might be offspring telomere length. Telomeres are protective caps at the ends of chromosomes; they function a bit like the plastic caps at ends of shoelaces and protect the coding DNA from loss during cell division. Telomere loss reduces the lifespan of cells and is thought to be involved in the ageing process. Individuals with longer telomeres or slower rates of telomere loss have been shown to live longer in a wide range of species. There is evidence that the offspring of older parents have shorter telomeres, but it is not clear whether this is due to the offspring inheriting shorter telomeres, or if their telomere loss during pre or postnatal growth is higher. We examined the relationship between the age of the parents and the telomere length of their offspring in a long-lived seabird, the European shag. We found that when the chicks first hatched, there was no effect of parental age on offspring telomere length, suggesting that there were no pre-natal effects of parental age. However, chicks produced by older parents had greater telomere loss during nestling growth than chicks produced by younger parents. These results are consistent with the hypothesis that the age of the parents influences offspring longevity in part through its effects on offspring telomere loss during post-natal growth. This could be due to a link between the quality of care that offspring receive and their telomere loss. Poorer quality care provided by older parents during post-natal growth could increase offspring stress and telomere loss. Such poorer quality care might occur because older parents are senescent, or perhaps because those parents that put less effort into rearing their offspring are more likely to live to be old.

    Image caption: Incubating shag. Photo provided by Mark Newell.
    You can read the article in full here.

     

    Ecological relevance of cellular energy metabolism in intertidal species

    Yun-wei Dong & Shu Zhang After a summer thundershower, a limpet, Cellana toreuma, habitat on a rocky shore in Dongshan, Fujian, PR. China.

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    Rocky intertidal ecosystems face some of the harshest environmental stresses on earth and are also one of the ecosystems most vulnerable to climate change. At low tide, animals living on the rocky shore frequently face high temperature, episodic heavy rainfall and other physical conditions. These stressors can at times be lethal, but, even if sublethal, they can reduce or eliminate growth and reproduction. To cope with sublethal stress, more energy has to be produced to repair stressor-induced damage.

    A group of proteins called metabolic sensors are gauges of cellular energy status and can effectively regulate cellular energy production. When cellular energy level is low, the levels of genes encoding such energy sensors as AMP-activated protein kinase (AMPK) and histone/protein deacetylase sirtuin (SIRT) can be elevated. The increased levels of these genes can lead to more energy generation from improved breakdown of glucose and lipids.

    In order to study cellular energy responses to high temperature, desiccation and freshwater spray (simulated rainfall), we measured the expression of genes involved in energy sensing, energy production, and energy expenditure in an intertidal limpet Cellana toreuma. During a three-day period, animals were maintained at different temperatures (18 or 30°C). Every day at 16:00-18:00, they were either aerially exposed or freshwater sprayed. Based on the gene expression patterns, all individuals could be divided into three groups. The different gene expression patterns in the three groups indicated a sequence in which individuals from group 1, group 2 and group 3 were faced with increasing shortage of energy. The frequency distributions of individuals in the three groups were different among treatments, indicating that high temperature, desiccation, and rainfall, singly or in combination, could all cause energy stress The genes examined in this study provide a validated set of indices (biomarkers) for quantifying environmental stress, including future stress from climate change, in this and, likely, other animals exposed to harsh conditions in the rocky intertidal zone.

    Image caption: After a summer thundershower, a limpet, Cellana toreuma, habitat on a rocky shore in Dongshan, Fujian, PR. China.
    You can read the article in full here.

     

    Top-down becomes bottom-up: consequences of nutrient cycling for trophic cascades between green and brown webs

    Kejun Zou, Elisa Thébault, Gérard Lacroix and Sébastien Barot An oxbow lake of Bandama River, Côte d’Ivoire. Photo by Gérard Lacroix.

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    Food webs represent trophic (feeding) interactions among species in ecosystems. Top-down trophic cascades in food webs are key to understanding population dynamics and ecosystem functioning. For example, because fish consume zooplankton that feed on algae, the removal of fish can increase the abundance of herbivorous zooplankton and strongly decrease the abundance of algae. Such trophic cascades are widely studied in classical food web theory, where the green (based on primary producers such as plants on land and algae in water that produce organic matter through photosynthesis) and brown food webs (based on decomposers such as bacteria and fungi that break down detrital organic substances) are usually studied separately.

    Studies on trophic cascades have so far ignored that nutrient cycling connects green and brown food webs. Nutrients that cannot be assimilated or are lost from organisms can either be returned directly to the nutrient pool (direct cycling), or indirectly through decomposition processes performed by decomposers of the brown food web (indirect cycling). The recycled nutrients support primary producers in the green food web but also decomposers when their growth is limited by mineral nutrients and not by carbon.

    We developed a simple food web model to explore the consequences of nutrient cycling for cascading effects between green and brown webs. We found that top-down effects propagate from one web to the other in a bottom-up way to affect ecosystem production. We show that on the one hand, since direct recycling immediately supports the growth of primary producers, predators of decomposers in the brown food web can increase or decrease primary production depending on whether they release more or less nutrients directly than decomposers. On the other hand, top predators of the green food web decrease or increase decomposer production depending on whether decomposers are carbon or nutrient limited. These results could be useful to ecosystem management where human activities strongly impact nutrient fluxes worldwide. For example, they could allow the improvement of agricultural practices through the management of belowground-aboveground interactions, or taking better account of the effects of recycling processes when using biomanipulation techniques for improving water quality.

    Image caption: An oxbow lake of Bandama River, Côte d’Ivoire. Photo by Gérard Lacroix.
    You can read the article in full here.

     

    Reseeders benefit from arid climates and infertile soils

    Rafael O. Wüest, Glenn Litsios, Félix Forest, Christian Lexer, H. Peter Linder, Nicolas Salamin, Niklaus E. Zimmermann, Peter B. Pearman Restioid fynbos at the Roikloof dam near Ceres, South Africa. Photograph: R. O. Wüest.

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    Fire is a key factor that impacts vegetation structure, composition and biodiversity both globally and locally. There is growing evidence that the effects of fire could be mediated by a basic life history trait: the ability of species to resprout after fire (resprouters) or the need to germinate from seeds (reseeders). Theory predicts that the relative proportion of resprouters in the vegetation should increase with increasing soil fertility and decreasing aridity, but little is known about how reseeders and resprouters are distributed in local plant communities with respect to environmental conditions.

    The Cape Floristic Region, one of the Earth’s richest biodiversity hotspots, is to a large degree covered by fynbos vegetation. The evergreen rush-like Restionaceae family of the grass-order Poales dominate many fynbos vegetation types. These vegetation types burn frequently, grow on diverse soils with distinct levels of fertility and are exposed to various climatic conditions. This makes the Restionaceae of the Cape Floristic Region an ideal study system to investigate how aridity and soil fertility relate to the relative proportion of resprouters and reseeders in the vegetation.

    Our results show that the relative proportion of resprouters is lowest in arid and unproductive conditions that do not allow for fast accumulation of biomass, i.e. fuel for fires. The resulting low fire frequency allows reseeders to complete their regeneration cycle between fires and occur at relatively high frequencies. On infertile soils, a decrease in aridity leads to faster biomass (fuel) accumulation and more frequent burning. This results in higher fire frequencies, which prohibits reseeder regeneration and favors resprouters because they can rapidly recover fire-induced vegetation gaps by resprouting from roots that survive fires below ground.

    While decreasing aridity on infertile soils leads to increased fire frequency, the contrary relationship is expected on fertile soils. A decrease in aridity on fertile soils slows down drying of available fuel, leading to lower fire frequencies, which potentially eliminates the advantage of resprouters over reseeders. Indeed, our results suggest that aridity and soil fertility interact in complex ways to determine the relative proportion of resprouters in the Cape Floristic Region.

    Image caption: Restioid fynbos at the Roikloof dam near Ceres, South Africa. Photograph: R. O. Wüest.
    You can read the article in full here.

     

    How do soil respiration components and their specific respiration change with forest succession?

    Wenjuan Huang, Tianfeng Han, Juxiu Liu, Gangsheng Wang and Guoyi ZhouForest succession in subtropical China. Photo credited to Xuli Tang, Qianmei Zhang and Yunting Fang.

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    Soil respiration usually includes two parts: heterotrophic respiration (RH) and autotrophic respiration (RA). The former refers to CO2 (or C) release through microbial decomposition of soil organic matter, while the latter primarily denotes respiration by roots themselves and microbial decomposition of carbohydrates derived from live roots. It is still unclear how soil respiration components change during forest development from its early to later stages (‘succession’). Based on Odum’s theory of ecosystem development, it has been hypothesized that the ratio of respiration to biomass (specific respiration) is likely to decrease with forest succession because forests tend to evolve towards less energy-wasting (i.e. a reduced ratio of maintenance to structure). However, this hypothesis has seldom been tested on the specific soil respiration components.

    In this study, we practically separated total soil respiration into RH and RA using a trenching method in three successional forests in subtropical China. This method can effectively prevent tree roots from entering a dedicated volume of soil so that RH can be measured. The results showed that RH in the growing season was significantly greater in the old-growth forest than in two early-stage forests. RA in the old-growth forest also tended to be the highest among the three forests, but specific RH and specific RA showed a declining trend with forest succession. Our results highlighted the importance of forest succession in determining the variation of RH and RA. The relatively high efficiency of the old-growth forest may suggest an important mechanism for increasing C storage in subtropical soils.

    Image caption: Forest succession in subtropical China. Photo credited to Xuli Tang, Qianmei Zhang and Yunting Fang.
    You can read the article in full here.

     

    To sprout, or not to sprout: freezing temperature drives spring flushing

    Armando Lenz, Günter Hoch, Christian Körner and Yann VitasseA mixed forest in the French Pyrenees on May 1 2007. Beech trees already started to sprout, when temperatures suddenly dropped and it began to snow, while less freezing resistant tree species have their leaves still in the protection of the buds. Photo credit: Y. Vitasse.

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    For trees, as for any other organism, frost is a major determinant of the annual life cycle in the temperate and boreal zones. Deciduous trees shed their leaves in autumn and form winter-hardy buds that contain the new leaves for next spring. In the buds, young leaves are well protected from freezing temperatures in winter. The time when trees sprout differs remarkably among species growing at the very same site within a forest. For instance, rowan or wild cherry sprout more than a month earlier than maple or European beech, even if they grow side by side and experience the very same climate. But why do different tree species sprout at different times within the same climatic conditions? Since leaves are safe from freezing damage as long as they are packed into a bud, but become very vulnerable as soon as the bud opens, the timing of bud-break should reflect the species-specific ability to tolerate freezing temperatures in the newly emerging leaves in spring. We compared long-term records of low temperature extremes in spring with long-term observations of sprouting from low and high elevations in Switzerland, as well as the species-specific resistance of emerging leaves to freezing temperatures. Our study revealed that across all species studied, sprouting occurs exactly at the time when the risk of frost damage approaches zero. The variation in sprouting among temperate tree species can thus be explained by the species-specific freezing resistance of newly emerging leaves. Spring phenology ensures tree survival in an ever more variable climate.

    Image caption: A mixed forest in the French Pyrenees on May 1 2007. Beech trees already started to sprout, when temperatures suddenly dropped and it began to snow, while less freezing resistant tree species have their leaves still in the protection of the buds. Photo credit: Y. Vitasse.
    You can read the article in full here.

     

    Survival benefits of winter dormancy: warmer climates are associated with shorter hibernation seasons and reduced survival in rodents

    Christopher Turbill and Samantha PriorCommon dormouse (Muscardinus avellanarius). Image provided by authors.

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    Doing nothing can have important benefits. Many animals spend the temperate winter season in a state of dormancy. In mammals, seasonal dormancy (hibernation) is facilitated by employing periods of deep torpor, when metabolic energy expenditure is reduced to a trickle. Torpor, in combination with pre-winter fattening or food storage, permits even mouse-sized hibernators to forego all external foraging activity for a large proportion of the year.

    The principal cost of activity is an increase in risk of mortality, especially from predation. Hibernation may appear to make mammals vulnerable to predation but in fact mortality rates while hibernating are five times lower compared to the active season. Enhanced survival over winter allows hibernating mammals to exhibit relatively slow life-histories (slow rates of growth and reproduction) compared to their non-hibernating counterparts.

    To understand the ecological function of seasonal dormancy in mammals, we analysed published data to test for associations among local thermal climate, duration of hibernation and annual survival rate in hibernating rodents. Annual temperature is known to be linked to a negative relationship between activity and survival among lizard populations. We hypothesised that local thermal conditions might underlie an analogous pattern in annual survival rates of hibernating rodents.

    We found that mean annual temperature is negatively associated with hibernation duration and annual survival rate in hibernating rodents (but not in a representative sample of non-hibernating rodents). A straight-forward explanation is the known positive effect of dormancy on survival (i.e. in colder climates, a greater proportion of the year is spent in the relative safety of hibernation). Thus seasonal dormancy has a positive effect on annual survival even in mammals. Our results suggest that shortening of winter hibernation owing to global warming will reduce annual survival rates (by 5% per 1 °C warming). Reproductive output might increase under longer growing seasons, but this compensatory effect is likely to be constrained. Our study highlights an important yet unappreciated mechanism leading to impacts of global climate change on animal populations in temperate climates.

    Image caption: Common dormouse (Muscardinus avellanarius). Image provided by authors.
    You can read the article in full here.

     

    Which is more important: direct environmental effects, or local adaptation, in determining how many times animals reproduce?

    Lin Schwarzkopf, M. Julian Caley and Michael R. KearneyImage provided by authors.

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    When should organisms be born? How big should they grow? When should they have have babies? How often, and how many? The answers to these questions for most organisms, including humans, depends on environmental conditions, but this is especially true for ‘cold-blooded’ ectotherms. In warm conditions, ectotherms should reproduce more, and more quickly, and grow more quickly than in cooler conditions. There are, however, many other factors that influence growth and reproduction, and so determining the relative influence of environmental temperatures can be difficult. We examined the number of reproductive events in populations of a geographically widespread, viviparous lizard, with an unusual life history, as a model system to examine the influence of environmental temperature on life history. Most viviparous lizards reproduce only once per annum, or even less frequently, but the lizard we examined reproduced twice per year in the tropical parts of its range. We modelled the entire life history of these lizards using a Dynamic Energy Budget model parameterised using data for this species, and predicted reproductive output assuming unrestricted food intake, and thermoregulation based on predictions from environmental models of available temperatures. Although we had to make a range of simplifying assumptions, the model was remarkably good at predicting the observed levels of reproductive frequency for these lizards, strongly suggesting that environmental temperature, rather than local adaptation, was the critical determinant of reproductive frequency. The model also suggested, however, that in locations where second reproductive events were possible, but likely to be risky, real lizards produced only one litter, as we might expect from natural selection to avoid costly mistakes, evidence for some local adaptation. Overall, our paper suggests that environmental temperature, and its direct effects on physiological rates, was critically important to the life history of this organism.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Temperature-dependence of fish performance in the wild: links with species biogeography and physiological thermal tolerance

    Nicholas L. Payne, James A. Smith, Dylan E. van der Meulen, Matthew D. Taylor, Yuuki Y. Watanabe, Akinori Takahashi, Teagan A. Marzullo, Charles A. Gray, Gwenael Cadiou & Iain M. SuthersSand whiting Sillago ciliata. Image Credit: Nick Dawkins.

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    It is well known that temperature has a strong influence on the performance, growth, and fitness of ectothermic (“cold-blooded”) animals. However most of our understanding comes from studies of animals in captive laboratory settings. Unlike in the laboratory, ectotherms in the wild need to balance the influence of temperature on their physiology (e.g. rates of metabolism or enzyme reactions) with a need to eat, avoid predation, compete and also reproduce, but we have little understanding of how temperature influences performance of ectotherms in their natural habitats.

    We measured body activity and growth rates in the wild for fishes from nine species, and across a broad range of temperatures. Temperature had a strong influence on fish performance in the wild, and in terms of both body activity and growth rates, the more-tropical species performed best in the wild at higher temperatures than did species with more-temperate distributions (tropical species had higher “optimum temperatures”). The tropical species also tended to have optimal temperatures that were closer to the highest temperatures they experience throughout their geographical distributions than did temperate species; temperate species generally maintained a larger “buffer” between their optimum temperatures and the warmest temperatures encountered in their natural range.

    We were also interested to know whether the trends seen in our wild data reflect trends seen in earlier physiological studies of how temperature influences performance in captive fishes. We compiled published, laboratory-derived data on fish aerobic scope – the difference between minimum and maximum metabolic rates – and found that the buffer which wild fish maintain (between their optimum performance temperatures in the wild and the highest temperatures in their range) is very similar to the difference between the optimum temperature for aerobic scope and the critically high temperature where aerobic scope plummets to zero in the laboratory.

    The combination of data from the field and laboratory highlights the major influence of temperature on ectotherm performance, and shows how closely the influence of temperature on physiology (in this case aerobic scope) seems to translate into patterns of performance in the wild. Interestingly, these data also suggest that fish species tend to perform best in the wild near the highest temperatures they encounter in their range, while maintaining a “safety margin” from the negative effects of critically high temperatures.

    Image caption: Sand whiting Sillago ciliata. Image Credit: Nick Dawkins.
    You can read the article in full here.

     

    Decoupled root and leaf decomposition in trees

    Chengen Ma, Yanmei Xiong, Le Li, Dali GuoRoots and leaf litter in the monoculture plantation of Acacia crassicarpa. Photo credit: Chengen Ma.

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    Conceptual frameworks describing how measurable plant characteristics (plant functional traits) influence ecosystem processes have been based largely on observations of aboveground traits. Recently, belowground traits and processes are receiving more attention. Several studies have proposed the “whole-plant economics spectrum framework” in which species with “fast” leaves (high nutrient concentrations, short lifespan, fast physiological rates and fast decomposition rates) also have “fast” roots, leading to fast ecosystem processes, whereas species with “slow” leaves have “slow” roots, and therefore “slow” ecosystem processes. Under this whole-plant economics framework, root traits and root decomposition mirror leaf traits and leaf decomposition, thus one can be predicted from the other.

    In this study, we showed that plant chemical traits were highly correlated between root and leaf litter across 18 tree species. However, root and leaf litter decomposition rates were significantly correlated only when the most easily-decomposed carbon is available, but it took only three months in our lab incubation to consume this labile carbon fraction. For the remaining 12 months of our 15-month long incubation, root decomposition rates were very low and no longer correlated with leaf litter decomposition rates.

    Decoupled root and leaf litter decomposition has several implications for better understanding plant-soil feedbacks. First, root and leaf litter need to be considered separately when evaluating their role in plant-soil feedbacks. Second, roots of woody plants seem to have tissue chemistry highly resistant to decomposition. This high tissue recalcitrance should be better understood in the future. Finally, due to the recalcitrant nature and slow decomposition of roots, roots may contribute disproportionately more to stable soil organic matter than leaf litter. In conclusion, our results clearly showed that decomposition of roots and leaves in woody plants are decoupled for the majority of litter mass, thus whole-plant “fast-slow” economics theory cannot be used as a predictive tool for ecosystem processes such as decomposition, at least in woody plants.

    Image caption: Roots and leaf litter in the monoculture plantation of Acacia crassicarpa. Photo credit: Chengen Ma.
    You can read the article in full here.

     

    Functional strategy composition is a good indicator of species dynamics

    Péter Török, Enikő T-Krasznai, Viktória B-Béres, István Bácsi, Gábor Borics and Béla TóthmérészThe Szűcs-Holt-Tisza oxbow sampling site in summer.

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    The humpback model of Grime is a popular model of the species richness versus biomass relationship. This model predicts that species richness displays a unimodal curve along a wide gradient of biomass with a peak at an intermediate level of biomass. Originally, the humped-back model was about terrestrial vegetation, and most papers presenting the model report studies of terrestrial plant communities. To provide new insights, the study of the relationships within phytoplankton assemblages is essential to help explain the coexistence of species. The analogues and other similarities between phytoplankton and terrestrial vegetation will help elucidate the dynamics and mechanisms that support diversity. Groups of functionally similar species are essential to understanding the dynamic processes in phytoplankton assemblages because of the extremely high number of species.

    We hypothesized that changes in the taxonomic diversity of phytoplankton along a biomass gradient are associated with altered functional diversity. For the analyses, 768 samples were collected from 30 oxbows, reservoirs and lakes in the Hungarian Lowland Region and analysed between 1992 and 2002.

    We found that the diversity and also the number of functional species groups showed a humped-back curve similar to the species richness curve, which indicates that the changes in functional group composition is a good proxy for phytoplankton species responses. The peak of species richness tended to occur towards the high biomass scores (>60% of the biomass range) compared to terrestrial plant communities (typically 20-60%). We found that the peaks of the number of strategy groups and of a diversity index (which accounts for how evenly individuals are distributed within species) were at a much lower biomass than that of species richness.

    The Cyanoprokaryota (‘blue-green algae’) were positively correlated with increasing biomass and negatively with the increase in species richness; thus, the high increase in their abundance and/or biomass can be responsible for the abruptly decreasing part of the humped-back curve. Our findings revealed fine-scale effects of increasing dominance of this species group with increasing biomass. This increase was clearly indicated by changes in the functional characteristics: first, the species evenness; then, the diversity index; and finally, the species richness started to decrease with increasing biomass.

    Image caption: The Szűcs-Holt-Tisza oxbow sampling site in summer.
    You can read the article in full here.

     

    Individual decision-making by prey may affect the strength of food chains

    Sarah A. Gravem and Steven G. MorganLeptasterias and Tegula. Photo provided by authors.

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    It is common for the state of an individual prey to influence its response to predators. For example, satiated or vulnerable individuals may be more inclined to cease foraging and flee from predators than hungrier or less vulnerable individuals. It is also well known that predators can benefit primary producers (e.g. plants and algae) by causing prey to graze less. However, these two concepts are rarely considered together; behavioral studies seldom test whether state-dependent prey behavior affects organisms lower on the food chain, and studies of food chains usually assume all individuals behave similarly. However, predators may strongly benefit primary producers when satiated or more vulnerable prey flee, but predators may exert no benefit on primary producers when hungry or less vulnerable prey ignore the predator and continue to graze.

    We strengthened the link between individual behavior and community outcomes by testing whether the effect of predators on primary producers hinged on the hunger level or size of the prey. In rocky intertidal tidepools in California, the small predatory seastar Leptasterias spp. can cause its abundant herbivorous snail prey Tegula funebralis to flee tidepools, which benefits tidepool algae. Using short experiments during low tide in the field, we showed that this benefit was strong when snails were well fed or medium-sized because these snails fled tidepools and grazed less. However, the benefit to algae by seastars disappeared when snails were hungry or small because the snails continued grazing or ate very little algae, respectively. Though our experiments suggest that large snails were nearly invulnerable to seastar predation, many fled from seastars. However, those large snails remaining actually grazed faster when seastars were present, so in this circumstance seastars had unexpected negative effects on algae.

    Because hunger level and size may vary predictably over time and space in nature, the cascading benefits to algae by predators may be patchy. We demonstrate that the common assumption that individuals in a food web are the same may not accurately predict outcomes. Further, state-dependent individual behavior of prey can cause domino effects on lower trophic levels. This approach strengthens our knowledge of the links between individual processes and community outcomes.

    Image caption: Leptasterias and Tegula. Photo provided by authors.
    You can read the article in full here.

     

    When does clumping help insects escape parasitism?

    Richard M. Gunton and Juha PöyryNatural History Museum.

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    Insects often find themselves hosts to parasitoids: other insects that lay eggs inside or close by them, so that the host is attacked and killed by the larva of the parasitoid. Although repulsive to humans, parasitism can provide useful biological control of certain crop pests. For this to be realistic, the attacks must follow certain kinds of patterns in space, so that the pest cannot simply escape by living in clumps, for example. A primary question is whether the per-capita risk of a host being attacked is higher or lower for denser clumps of hosts: do parasitoids target denser clumps enough to limit their role as refuges?

    We combined data from 61 studies of parasitism rates to expore factors relating to whether the risk of parasitism goes up or down when a host lives at higher densities. We found that it normally goes up, but species characteristics can make a difference: exotic hosts are much more likely to reduce their risk by living at higher densities than are native hosts, and exotic parasitoids, and also smaller ones, produce the same phenomenon. At the same time, the taxonomic group that a host insect comes from seems to make a difference. For example, an exotic moth or beetle is likely to suffer more for living at lower densities, especially if a larger exotic parasitoid is hunting it.

    But we also have to consider the way a study is performed. Parasitism risks have to be calculated by counting up the proportions of hosts attacked within patches of a certain area, and we found that studies using larger areas (e.g. 1-ha plots in a field) tended to find risks increasing with density more than those that used smaller areas (e.g. single leaves). But here lies a mystery: individual studies comparing different areas don’t seem to find any consistent effect.

    We conclude that ecological context is very important, and more work is needed. We hope that our findings will help improve the design and interpretation of studies on parasitism as well as how they get applied to population dynamics models and biological control on the farm.

    Image caption: Natural History Museum.
    You can read the article in full here.

     

    Do invaders most strongly impact similar species?

    Erica. J. Case, Susan Harrison, Howard V. Cornell Image provided by authors.

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    Although invasive plants may eliminate some resident species at local scales, they seldom cause region-wide extinctions. One possible explanation is that highly successful invaders tend to be functionally similar to, and therefore compete most strongly with, resident species that are also relatively successful and widespread. High abundance may then buffer these functionally similar residents from complete extinction over large areas despite their stronger competition with the invader.

    We examined whether greater declines among abundant species could be explained by greater resemblance to the invader in a diverse, species-rich Californian serpentine grassland invaded by Aegilops triuncialis (barb goatgrass). We calculated the relative change of each resident species’ abundance in invaded plots compared to paired uninvaded plots, and explored whether this change correlated with abundance and/or functional resemblance to Aegilops.

    We found Aegilops most strongly impacted other annual grasses, which are more abundant than other functional groups. However, we did not find a relationship between regional declines, functional resemblance to the invader, or abundance in general. Additional factors, such as varying environmental conditions, must contribute to the relative scarcity of large-scale extinctions under invasion.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Tree resprouting and carbohydrate allocation

    Rei Shibata, Hiroko Kurokawa, Mitsue Shibata, Hiroshi Tanaka, Shigeo Iida, Takashi Masaki and Tohru Nakashizuka The Ogawa Forest Reserve (upper) and the surrounding secondary-growth stand (lower), Japan. Photo by Toru Nakashizuka.

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    Many woody plants possess the ability to resprout and restore the aboveground biomass lost during a disturbance. Resprouting is an important trait of woody plants that increases their survival in forest environments, even if major disturbances are rare. Resprouting requires the storage of photosynthates at the expense of other investments such as growth and reproduction. This resource allocation trade-off may affect species co-existence, but the general relationship between resprouting ability, carbohydrate storage, and other traits remains unclear.

    In this study, we investigated the relationships among root and shoot contents of total nonstructural (i.e. storage) carbohydrates (TNC), root mass ratio (root dry mass/total dry mass), resprouting ability, and species’ traits for 24 co-occurring deciduous broadleaved woody species in a cool-temperate forest in Japan. We defined two resprouting groups: single-stemmed species that resprout only after aboveground damage, and multi-stemmed species that resprout without requiring aboveground damage.

    Single-stemmed species with greater resprouting ability in the juvenile and mature stages had larger roots and higher root TNC content, suggesting that they store large belowground carbohydrate reserves to support resprouting. On the other hand, multi-stemmed species with greater resprouting ability did not have larger belowground carbohydrate reserves.

    Traits associated with light-demanding species (high foliar nitrogen and low wood density) were related to large root TNC reserves for single-stemmed species. This may represent a resource allocation trade-off between physical defences (e.g., tough wood) and large belowground reserves, and having a high photosynthetic rate (high foliar nitrogen) could allow greater allocation to belowground reserves in addition to fast growth of aboveground parts for these species. On the other hand, we found no trade-offs between belowground reserves and other traits for the multi-stemmed species. We hypothesized that the smaller species would allocate more photosynthate to belowground reserves, but found no such relationships for the single- and multi-stemmed species.

    This is the first demonstration that contrasting carbohydrate allocation and resprouting patterns among single-stemmed and multi-stemmed species, and variations in the underlying resource allocation trade-offs, affect species co-existence in a cool-temperate forest.

    Image caption: The Ogawa Forest Reserve (upper) and the surrounding secondary-growth stand (lower), Japan. Photo by Toru Nakashizuka.
    You can read the article in full here.

    The functional role of silicon in plant biology

    Silicon in aquatic vegetation

    Jonas Schoelynck & Eric Struyf Researchers from Antwerp, Lund and Maun on their 2012 expedition to study the silicon cycle in the Okavango Delta, the largest inland delta in the World. Courtesy of D.J. Conley.

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    Most people think about sand, computers or glass when they hear about silicon (Si). However, silicon intrudes much more deeply into our daily lives. It is found in drinks (e.g. beer), in crops (e.g. rice), in cosmetics (e.g. shampoo)… it is basically everywhere. This is not surprising since silicon is the second most abundant element on the planet. It is a major constituent of rocks and soils and it only slowly dissolves from this massive Si pool. This dissolved silicon is transported through rivers to the coasts, where single-celled organisms feed on it, and take large amounts of CO2 from the atmosphere during their growth. This intimate link with carbon strongly influences the climate on Earth. We now know that most of the dissolved silicon is taken up by plants during this transport from land to water. Plants store it as ‘phytoliths’, tiny silica ‘plant stones’. The painful cuts when pulling sharp grass are often caused by tiny silicified ‘razor blades’ on the grass leaf surface. In contrast to the physical and chemical dissolution from rocks, this biological control on the silicon cycle has only recently been acknowledged by science. Improving our understanding of this bio-control is important: Si is an essential nutrient that influences the health of many ecosystems. Up to now, only a few researchers have studied the effects of aquatic vegetation on the silicon cycle. Still, the knowledge available shows that aquatic vegetation can store significant amounts of the element. It alleviates stress by fast current velocities, nutrient limitation and herbivory, and potentially aids in the photosynthetic process. Si also determines decomposition processes of decaying water plants. This is especially important in large rivers and wetlands (such as the Okavango Delta in Botswana, see picture) where the majority of the silica is stored in the organic matter of the sediments. This review provides an overview of the state-of-the-art of knowledge on silicon in aquatic vegetation.

    Image caption: Researchers from Antwerp, Lund and Maun on their 2012 expedition to study the silicon cycle in the Okavango Delta, the largest inland delta in the World. Courtesy of D.J. Conley.
    You can read the article in full here.

     

    City slickers: poor performance does not deter Anolis lizards from using artificial substrates in human-modified habitats

    Jason J. Kolbe, Andrew C. Battles, and Kevin J. Avilés-RodríguezA male Anolis cristatellus feeding while perched at the top of a brick wall.  Photo by Jason J. Kolbe.

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    How do lizards adjust to life in the city? Urbanization transforms natural environments into a mix of buildings, roads, parks and natural habitats. Through this process, humans are creating novel environments for other organisms. For example, we add artificial substrates, such as buildings, fences, posts, and walls, which become part of the structural habitat of a city. Lizards may use these novel substrates as they do trees in natural forests, but their performance ability on these substrates may be altered.

    In this study, we tested how lizards run on substrates that differ in inclination and roughness. We compared rough surfaces like the trunks and branches of trees in the forest to the smooth and vertical surfaces typical of posts and walls in the city. Then we investigated whether lizards use artificial substrates when they are available in human-modified areas. Lizards living in natural environments tend to use habitats in which they perform better. In contrast, lizards in human-modified areas do not avoid the artificial substrates on which they perform poorly. Lizards run slow as well as slip and fall on smooth, vertical surfaces, yet they often use posts and walls when available in human-modified areas. Despite their poor performance, lizards with longer limbs run faster and fall less when moving on smooth, vertical surfaces. From this relationship we predict that natural selection will favor lizards with longer limbs when they use artificial substrates in cities.

    Human-induced global change such as biological invasions and urbanization may fundamentally alter the ecological relationships found for organisms living in natural environments. This makes predicting the consequences of global change extremely difficult. Moreover, human-altered environments are likely to be strong sources on natural selection for the organisms that can persist there.

    Image caption: A male Anolis cristatellus feeding while perched at the top of a brick wall. Photo by Jason J. Kolbe.
    You can read the article in full here.

     

    Coexistence resulting from being more different or more similar?

    Lin Zhao, Quan-Guo Zhang and Da-Yong ZhangBacterial colonies growing on nutrient agar plates.  Competing strains are distinguishable by their colony colors. Picture by Lin Zhao.

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    The conventional wisdom of the ‘competitive exclusion principle’ in ecology stresses the importance of being different for stable species coexistence. It states that two species competing for the same niche (say, using the same resources and the same habitats) cannot coexist; and evolutionary thinking suggests that related species, when competing with each other in their overlapping ranges, will evolve toward greater differences in their niches, which in turn alleviates competition and promotes stable coexistence. The recently emerging neutral theory in ecology, however, highlights the importance of being similar for species coexistence, that is, species that use the same niche but also have the same competitive ability can co-occur for a very long time. However, how neutrality among species could emerge in the first place remains unclear. One possibility is that populations of related species that evolve in isolation show convergence in both niche use and competitive ability, and thus become ecologically equivalent competitors. Such species may form a ‘neutral community’ when they have a chance to colonize the same habitat (secondary contacts).

    We carried out an experimental evolution study with laboratory bacterial populations. Bacteria can grow fast and thus their evolutionary changes can be observed in real time. Several pairs of Escherichia coli strains that showed niche differences were used to examine how evolution alters coexistence mechanisms. When bacterial strains were allowed to evolve under competition for over one thousand generations, niche differences among them were maintained. Strains that evolved in isolation showed convergence in niche use, but not in competitive ability. Therefore, our work fails to provide support for the possibility that convergent evolution creates equivalent competitors and leads to the emergence of neutral communities. The origin of neutral communities remains an open question.

    Image caption: Bacterial colonies growing on nutrient agar plates. Competing strains are distinguishable by their colony colors. Picture by Lin Zhao.
    You can read the article in full here.

     

    Evolution in space: metapopulation structure and life history evolution

    Annelies De Roissart, Nicky Wybouw, David Renault, Thomas Van Leeuwen & Dries Bonte Spider mites as a model for experimental evolution (mature female, on bean). Photo credit by Gilles San Martin.

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    Organisms live usually –not to say always- in heterogeneous environments. Habitat patches vary typically in size and connectivity, and this variation determines the local population dynamics, the exchange of individual among patches and the resulting synchronization of changes in population size. While there is a large body of theory on how changes in this ‘metapopulation’ structure affect demography and evolutionary dynamics, empirical evidence remains extremely scarce. Experimental metapopulations and experimental evolution are a strong tool to study these dynamics in a controlled manner.

    We installed replicated experimental sets of patches connected by dispersal (metapopulations) that vary in the spatial and spatiotemporal availability of habitat. The metapopulations were inhabited by spider mites living on bean leaf patches. Spider mites are arthropod herbivores with short generation times that are known to evolve fast in response to, for instance, host plant and pesticides. They are a serious pest in greenhouses. Our experimental metapopulations reflect the dominant metapopulation types in nature: a classical metapopulation consisting of equally sized patches where resources are randomly fluctuating, a patchy metapopulation with stable patches of similar size, and mainland-island metapopulations that are characterized by stable patches that differ in size.

    We earlier reported that this variation in metapopulation structure affects the local and metapopulation-level demography (< a href="http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12400/abstract">De Roissart et al. 2015 in Journal of Animal Ecology) and anticipated additional evolutionary changes in life history, physiology and gene-expression. By following a common garden approach to exclude environmental effects, we demonstrate strong evolutionary divergence in relation to metapopulation structure. Contrary to expectation from metapopulation ecology, no evolution in dispersal was found. Instead, the evolutionary changes could be attributed to local demographic variation, especially the degree of local competition and resource shortage. Patterns of life history evolution and especially changes in the expression of genes associated with several important metabolic pathways suggested that the evolutionary changes could be attributed to a general stress response. Such responses are known to allow organisms to cope with other unfamiliar stressors, and we indeed found that those mites that evolved in the stressed metapopulations performed better on this challenging host. Changes in habitat configuration and the emerging local dynamics thus induce the evolution of general stress responses that may reverse demographic threats due to other non-related environmental changes, a phenomenon known as evolutionary rescue.

    Habitat fragmentation and habitat loss are a major component of global change. Our experimental work demonstrates that changes in spatial configuration of the habitat alone can induce evolutionary dynamics of the inhabiting species, which eventually affect responses towards other environmental disturbances.

    Image caption: Spider mites as a model for experimental evolution (mature female, on bean). Photo credit by Gilles San Martin.
    You can read the article in full here.

     

    Soil microbial communities matter for carbon cycling during drought

    Kate H. Orwin, Ian A. Dickie, Jamie R. Wood, Karen I. Bonner, Robert J. HoldawayDifferent land uses in the Wairau Valley, taken by Robbie Holdaway.

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    Land use intensification results in changes in soil conditions (e.g. pH, total soil carbon and nutrient contents), the microbes that inhabit the soil, and the way in which soil carbon and nutrients are cycled between the soil, the atmosphere and plants. Soil microbes are the organisms that are primarily responsible for recycling the carbon and nutrients found in dead matter (leaves, roots animals). They are therefore fundamentally important for determining how much carbon is stored in the soil, and how fertile it is. However, because land use, soil conditions and soil microbial communities all change simultaneously across land use gradients, it is unclear whether the types, biomass, and diversity of soil microbes drive variation in carbon and nutrient cycling independently of land use and underlying soil resources. Further, we have a poor understanding of whether the main drivers of carbon and nutrient cycling are the same under both stable and disturbed conditions. Understanding this is particularly relevant given the projected increase in disturbance frequency (e.g. drought) under climate change. Here, we examined whether the types, biomass, and diversity of soil microbes were able to predict various measures of carbon and nutrient cycling under stable and disturbed (a simulated drought) conditions, after effects of land use and underlying soil conditions were taken into account. The land use gradient consisted of natural forest, planted forest, high- and low-producing grassland, and vineyards. Results showed that although measures of the soil microbial community were frequently correlated with carbon and nutrient cycling under stable conditions, they did not add any further predictive power once land use and soil conditions were accounted for. However, knowledge of the microbial community was essential to explain the response of carbon cycling to drought. This suggests that carbon cycling in the future may be strongly dependent on the characteristics of the microbial community.

    Image caption: Different land uses in the Wairau Valley, taken by Robbie Holdaway.
    You can read the article in full here.

     

    Heat hardening in a tropical lizard: geographic variation explained by the predictability and variance in environmental temperatures

    Ben L. Phillips, Martha M. Muñoz, Amberlee Hatcher, Stewart L. Macdonald, John Llewelyn, Vanessa Lucy and Craig MoritzCogger's sunskink, from Australia's Wet Tropics Rainforest.  Populations of this species show strong, predictable geographic variation in heat-hardening; a physiological trait of importance under climate change.  Photograph by Ben Phillips.

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    Climate change will place considerable stress on populations over the coming decades. Whether populations can adapt to these changes will depend on the levels of variation that are present in key traits, such as heat tolerance. In this paper, we show that a rainforest lizard (Lampropholis coggeri) has a strong heat-hardening response: a rapid increase in its capacity to withstand high temperatures following a brief exposure to high temperature. We then measure this trait in 13 populations spanning a range of climatic conditions. Our results reveal considerable variation in this important trait and show that this variation is stored across space, in locally adapted populations. By looking at underlying climatic variables (the seasonality and predictability of environmental temperatures), we also show that we can predict which populations will have the greatest heat-hardening capacity. Thus, our work demonstrates adaptive variation in an important trait, and also that we can predict which populations contain individuals with the greatest heat-hardening capacity. This ability to predict the location of important trait variation will prove invaluable to future efforts to use assisted gene flow (the assisted movement of individuals between populations to provide recipient populations with important genetic variation) to mitigate the impacts of climate change.

    Image caption: Cogger's sunskink, from Australia's Wet Tropics Rainforest. Populations of this species show strong, predictable geographic variation in heat-hardening; a physiological trait of importance under climate change. Photograph by Ben Phillips.
    You can read the article in full here.

     

    Oxidative stress changes how birds make decisions

    David Costantini, Giulia Casasole, Hamada AbdElgawad, Han Asard and Marcel Eens Canary, Serinus canaria. ©David Costantini.

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    Resources are finite; therefore allocation of a resource to one function, such as reproduction, means that less can be allocated to others, such as body maintenance. This simple concept, referred to as a trade-off, helps us understand the diversity among organisms in their rate of growth, reproductive rate, and longevity. A classic trade-off is that between reproduction and body maintenance because reproduction is generally held to be a demanding phase of animals’ lives, since they must produce, and in some cases protect and provision, their young. Hence, high investment of resources into reproduction means that less is available to protect the body against any processes that might damage it. One reason why individuals deteriorate is thought to be through accumulation of oxidative damage to tissues. The term ‘oxidative stress’ describes a state where oxidative damage to body tissues increases because oxidising molecules, which are mostly a by-product of metabolism, exceed the body’s level of antioxidant defences, and thus are free to react with molecules like lipids, proteins and nucleic acids. Such body deterioration may also in turn influence future investment in reproduction if it results in reduced fertility or changes in hormonal status. We examined whether a state of oxidative stress influences reproductive decisions (when and how many eggs to lay) and reproductive success (hatching and fledging success, number of hatchlings and fledglings produced) in females of a songbird (canary, Serinus canaria). Prior to the reproductive season, females were injected a substance that increases oxidative stress. Then females were mated with a non-relative male and their reproductive activity was followed. Those females whose oxidative stress level was increased delayed the start of egg laying and laid significantly smaller clutches than those females whose oxidative stress level was not increased. However, reproductive success was similar between control and stressed females. Our study provides a rare insight into the cellular mechanisms that constrain reproductive decisions under female control in a vertebrate.

    Image caption: Canary, Serinus canaria. ©David Costantini.
    You can read the article in full here.

     

    Air humidity thresholds trigger active moss spore release to extend dispersal in space and time

    Victor Johansson, Niklas Lönnell, Üllar Rannik, Sebastian Sundberg and Kristoffer HylanderThe peristome movements of Brachythecium rutabulum in response to relative air humidity (RH), when (a) open (RH; 40%), (b) closing (RH; 75%) and (c) closed (RH; 90%).

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    Plants that can disperse their seeds or spores over long distances can decrease competition with relatives, and can better sample their surrounding environment to ensure colonization of new suitable habitats. For species living in variable environments it may also be beneficial to spread dispersal over time. However, the dispersal processes, and especially what triggers the release of spores, is poorly understood for many species groups. One example is mosses – a group with approximately 12 000 species. Mosses disperse their spores from one or several capsules that are often elevated a bit above the shoot. Many species have a structure called a peristome in the capsule opening that closes in response to increasing air humidity and opens when dried, but the significance of this is unclear.

    Using the moss Brachythecium rutabulum, we investigate the importance of peristome movements for spore release, when the peristome movements occur in nature, and how this may affect dispersal distances. We did this based on spore release measurements in a humidity chamber in the lab, micrometeorological measurements close to the ground in nature, and spore dispersal simulations using a mechanistic dispersal model.

    We show that spores are released only when the peristome teeth open in response to decreasing humidity, which usually occurs in the morning. During spore release wind speeds are comparatively low, which contrasts with several studies of seed release. Nevertheless, the release mechanism seems to enhance dispersal distances, compared to mechanisms that release spores in higher wind speeds later in the day. The reason is that release in the morning results in more vertical dispersal of the light spores. The mechanism may also spread dispersal in time more than other known release mechanisms for moss spores.

    Image caption: The peristome movements of Brachythecium rutabulum in response to relative air humidity (RH), when (a) open (RH; 40%), (b) closing (RH; 75%) and (c) closed (RH; 90%).
    You can read the article in full here.

     

    Transgenerational plasticity and environmental stress: do paternal effects act as a conduit or a buffer?

    Annie S. Guillaume, Keyne Monro and Dustin J. MarshallImage provided by authors.

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    In most organisms, the early life-history stages are the most sensitive to environmental stress. Parents sometimes use cues from their environment to tailor their offspring to local conditions. This process, known as transgenerational plasticity, is thought to be critical for organisms that release tiny, vulnerable gametes, and may be important for buffering populations from the impacts of global change. Most studies of transgenerational plasticity have either focused only on the effect of mothers on offspring phenotype (maternal effects), or on the combined effect of parents on offspring phenotype – few have disentangled the relative effects of mothers and fathers (paternal effects) on offspring phenotype.

    We manipulated the water temperature that parents experienced prior to reproduction and measured the performance of offspring across temperatures. We used the marine tubeworm Galeolaria caespitosa, a broadcast spawning marine invertebrate that is an important habitat forming species in southern Australia.

    We found that the experiences of both parents affected gametes and larvae: fertilisation success and larval survival depended on the acclimation temperature of the parents. Surprisingly, paternal effects mattered more than maternal effects. We also found that the paternal effects often decreased offspring performance, especially when the temperature experienced varied compared to when the temperature was kept the same.

    Our results suggest that, while transgenerational plasticity may play an important role in modifying the impacts of global change, these effects are not always positive. Importantly, paternal effects can be as strong, or stronger, than maternal effects and environmental variability strongly alters the impacts of paternal effects.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Experimental effects of early-life corticosterone on the HPA axis and pre-migratory behaviour in a wild songbird

    Jesse J. Pakkala, D. Ryan Norris, James S. Sedinger and Amy E.M. Newman A banded Savannah sparrow perches upon a gooseberry shrub on its breeding territory, Kent Island (New Brunswick, Canada).  Photo credit: Stéphanie Doucet.

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    The early-life environment has profound and lasting effects on behaviour and physiology, which is especially obvious when the early-life environment involves exposure to severe stressors. For example, evidence from children born in the year of the Dutch Hunger Winter of 1945 is a potent example of the lasting effects of early-life stress. Although stress may be considered a so-called “fact of life”, how early-life stress influences the fitness of animals in the wild is not well understood. To understand such ecophysiological links, one must be able to follow individuals in their natural environment from birth to later-life stages, and have knowledge of the physiological effects of stress. The vertebrate stress axis, also called the hypothalamic-pituitary-adrenal axis (or HPA axis) is highly conserved among vertebrates and is an important mechanism that connects organisms to their environment. Stressors in the environment activate the HPA axis, causing an increase in circulating stress hormones, which have many downstream effects.

    Contrary to popular myth, Savannah sparrows are far more than mere ‘little brown jobs’. An experiment on a long-term, marked population breeding on a remote island in the Bay of Fundy has revealed how increased levels of stress hormones during the early days of life influence both the physiology of nestlings and their subsequent behaviour as independent juveniles. In an intensive field experiment, we examined hypotheses to explain stress exposure. Nestling sparrows treated with the stress hormone, corticosterone, on days 2-6 post hatch, were more sensitive (had higher circulating stress hormones) to inclement weather when they were 7 days old. And, importantly, after birds had fledged the nest, mark-recapture analysis revealed that early-life corticosterone exposure increased temporary emigration from the study site, highlighting an important carry-over effect of early-life stress on behaviour later in life. Tracking individuals across multiple stages of the life cycle will advance our understanding of how early-life stress and ecology interact to influence physiology, behaviour and fitness.

    Image caption: A banded Savannah sparrow perches upon a gooseberry shrub on its breeding territory, Kent Island (New Brunswick, Canada). Photo credit: Stéphanie Doucet.
    You can read the article in full here.

     

    The importance of biotic interactions for the prediction of macroinvertebrate communities under multiple stressors

    Nele Schuwirth, Anne Dietzel and Peter ReichertMayfly with eggs, taken by Nele Schuwirth.

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    In this study we tested a computer model to predict the occurrence of macroinvertebrates in streams. Macroinvertebrates are aquatic organisms that live on the river bed or in the sediment, like insect larvae, snails, worms, or crustaceans. They are very diverse and have different environmental requirements, e.g. regarding temperature, flow velocity, substrate types, water quality, and they are specialized on different food sources. Because their community composition depends on the environmental conditions, they can be used to assess the ecological state of rivers and the influence of human impacts, like water pollution, channelization, or modifications of the flow regime. For decision support in river management it is important to predict the influence of different management activities on the ecological state of the rivers. To this end, predictive models can be useful tools.

    Based on existing knowledge about the requirements of different macroinvertebrate taxa and some basic principles, like mass conservation or the scaling of vital rates with body-size and temperature, we constructed the process based model called "Streambugs". The model aims to predict which species, genera or families are expected to occur at which sites. We used existing monitoring data from 36 sites in the Glatt catchment at the Swiss Plateau to compare model predictions with observations. Even without fitting the model parameters (factors that influence growth, respiration and death processes) and just relying on prior knowledge about these parameters, for 79% of the taxa at the 36 sites the difference between the observed and predicted frequency of occurrence is less than 50%. This is considerably better (+18%) than a random model that assigns a 50% chance to observe or not observe each taxon at each site and each sampling event. By adjusting factors that increase or decrease the growth rates of the different organisms, we can increase model compliance with data. Furthermore, we tested which properties of the organisms contributed most to the predictive power of the model. In this catchment, sensitivity to organic toxic substances as well as feeding-types were most important for making good predictions. These results highlight that biotic interactions between the organisms (competition for food and predator-prey interactions) should be taken into account when trying to predict the occurrence of aquatic organisms in streams.

    Image caption: Mayfly with eggs, taken by Nele Schuwirth.
    You can read the article in full here.

     

    Diet determines movement rates and size of area used for herbivores

    Zulima Tablado, Eloy Revilla, Dominique Dubray, Sonia Said, Daniel Maillard and Anne LoisonPhoto provided by authors.

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    Mammalian herbivores have specialized on a variety of diets, ranging from species eating almost exclusively grasses (grazers) to species feeding mostly on browse, other herbaceous plants, and fruits (browsers). Since these vegetation types are not equally distributed in the space, species feeding on them should not move equally either. Moreover, grasses and therefore grazers are usually associated with open spaces (grasslands) in which animals are more easily detected by predators and tend to group in herds in order to maintain high levels of vigilance and decrease per capita predation risk. By contrast, browsers are linked to areas with protective cover (bushes and forests), rely more on hiding as a strategy to avoid predation, and are usually solitary. In-between these two extremes, we find the species called mixed feeders. In an area of the French Alps where three species of large herbivores coexist (roe deer, chamois, and mouflon), we marked individuals with GPS collars. We investigated how movement patterns and home ranges at different temporal scales differed for these three species, expecting shorter movements and smaller home ranges at all scales for browsers than grazers and intermediate species. Interestingly, no differences in movement occurred at fine temporal scale: all species move as much when looking for food (20 minutes time scale), whatever their diet. But differences emerged at larger scales (hours, day, season scales). As expected, mouflons, which are grazers and form large herds, performed larger displacements and depended on larger areas, probably as a results of competition within groups. Further, their movements and range areas were affected the most by environmental factors, such as weather and human disturbance, which occurred mostly in open areas. At the opposite extreme, roe deer, which are solitary browsers, performed smaller displacements, moving back and forth within smaller range areas. Their movements seem also to be less affected by the variability of external factors. Finally, chamois, which are mixed feeders, showed patterns that were intermediate between the other two species. Food distribution, feeding type, and local competition with related animals should be considered jointly to understand large herbivore movements, home range and response to external factors.

    Image caption: Photo provided by authors.
    You can read the article in full here.

     

    Impacts of toxic nectar on three pollinators

    Erin Jo Tiedeken, Paul A. Egan, Philip C. Stevenson, Geraldine A. Wright, Mark J. F. Brown, Eileen F. Power, Iain Farrell, Sharon M. Matthews, and Jane C. Stout Invasive Rhododendron ponticum.

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    Pollinator decline is a serious concern worldwide; pollinators are important for global food production, and they are also essential in maintaining the diversity of flowering plants on our planet. One cause of pollinator declines is thought to be the spread of highly abundant and ecologically damaging species beyond their native ranges (invasive alien species). Nevertheless, researchers still do not understand the direct impacts that invasive plants have on pollinators.

    In this study, we show that an invasive plant in the United Kingdom and Ireland, Rhododendron ponticum, has very different effects on three economically and ecologically important pollinating bee species. Rhododendron nectar was toxic to native Irish honeybees, killing individuals within hours of consumption. The nectar also had negative impacts on the foraging behaviour of a native Irish solitary bee. The solitary bees became paralyzed after feeding on Rhododendron nectar, and ate less food than bees fed a control nectar. In contrast, the native buff-tailed bumblebee was able to consume the nectar with no negative responses, even when the bumblebee was weakened by lack of food or parasite infection. Invasive Rhododendron may therefore provide an important novel nectar resource for this bumblebee species, especially in the early spring when bumblebee queens are establishing their colonies.

    Our study shows that the toxicity of Rhododendron nectar is due to the presence of a neurotoxin that humans are also susceptible to, called grayanotoxin I. Many plant species contain such “nectar toxins,” chemicals that are usually associated with defence against foliar herbivores. Our paper demonstrates that invasive plants may differentially impact pollinators, providing new food resources only to those that can tolerate their nectar toxins. In addition, this work demonstrates the importance of comparing the susceptibility of multiple species to natural and synthetic chemicals before making conclusions about the impact of substances on pollinators as a whole.

    Image caption: Invasive Rhododendron ponticum.
    You can read the article in full here here.

     

    Energy expenditure at rest affects reproduction and survival in house sparrows

    Bernt Rønning, Juli Broggi, Claus Bech, Børge Moe, Thor Harald Ringsby, Henrik Pärn, Ingerid J. Hagen, Bernt-Erik Sæther and Henrik JensenAfter the experimental period, birds were released at the same location as they were captured. Photo: H. Jensen.

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    The body must use a minimum amount of energy to keep all its systems functioning correctly. This rate of energy use, termed basal metabolic rate (BMR), has been measured in birds all over the world and found to vary between birds living in different environments. The fact that this trait is adapted to different environments implies that it has been shaped through natural selection and therefore probably is related to fitness, i.e. survival and reproduction. Despite this, we know surprisingly little about how BMR is related to fitness. One could expect that an individual which uses little energy to sustain its basic body processes i.e. has low BMR, has more energy available for producing offspring and staying alive, thereby enhancing fitness compared to an individual with high BMR. On the contrary, it may be that high BMR reflects a high working capacity. In other words, an individual with high BMR can eat more food and process it at a higher rate, thereby having more energy to spend on activities that increase fitness. To test the relationship between BMR and fitness in a songbird we measured BMR in two populations of house sparrows (Passer domesticus) in northern Norway. Thereafter, we collected data on how many offspring each bird produced and their survival from one year to the next.

    We found that, although there was an overall tendency for birds with low BMR to produce more offspring, this negative relationship was significant only for females in one of the populations. Furthermore, the relationship between BMR and survival also differed between sexes and populations. An effect of BMR on survival was found only in one population. In that population females with an average BMR were more likely to survive, whereas males with an average BMR were less likely to survive.

    The fact that the relationship between BMR and fitness diffed both between sexes and populations implies that this relationship may not be always either positive or negative as often predicted, but instead be context dependent, varying in time and space in relation to e.g. food availability and weather conditions.

    Image caption: After the experimental period, birds were released at the same location as they were captured. Photo: H. Jensen.
    You can read the article in full here.

     

    Short-term rainfall, not temperature, controls lizard microhabitat use in a piñon-juniper woodland

    Mason J Ryan, Ian M Latella, J. Tomasz Giermakowski, Howard Snell, Steven Poe, Robert E Pangle, Nathan Gehres, William T Pockman & Nate G McDowellImage provided by authors.

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    As climate change increases temperature globally and alters regional rainfall, the activity and foraging behavior of cold-blooded animals (ectotherms) like lizards must also change if individuals are to grow and reproduce. Lizards respond to higher temperatures by decreasing activity and reducing foraging time, particularly in sunlit locations, to limit heat gain. While these behavioral changes at higher temperature are linked to population declines, little is known about how lizards will respond to decreases in rainfall in arid environments predicted to accompany warming. Moreover, tests of these responses are difficult in natural environments because experimental manipulations of temperature and rainfall are uncommon.

    To examine how wild lizards respond to changing temperature and rainfall, we measured lizard responses in a piñon-juniper woodland in New Mexico where rainfall and temperature were manipulated on 40 x 40 m plots assigned to one of four treatments: Drought imposed by plastic troughs diverting 45% of natural rainfall, Warming plots with inverted plastic troughs that raised temperatures without diverting rainfall, Irrigation plots with sprinklers that simulated rainfall, and unmanipulated Control plots. In the context of these treatments, we observed lizards and recorded their activity and use of shade or sun microhabitats. This design allowed us to determine how rainfall and/or temperature influenced lizard activity and decisions about foraging in sun vs. the shade of trees.

    Contrary to recent studies, we found that rainfall, not temperature, strongly influenced lizard behavior. During dry periods, lizards foraged almost exclusively in shade under trees, whereas lizards foraged in sunny areas across the landscape following natural or simulated rainfall events. Temperature did not influence lizard behavior, even in the covered plots with the warmest temperatures, a surprising result considering the wealth of research showing lizard temperature sensitivity. We conclude that our study lizard is more sensitive to moisture and relies on tree shade as a refuge during dry periods. The long-term drying trends that are increasing tree mortality in piñon-juniper woodlands may decrease the availability of this critical lizard microhabitat.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Friend or foe? Lessons from cushion alpine plants and their neighbours

    Giuliano Bonanomi , Adriano Stinca, Giovanni Battista Chirico, Giampiero Ciaschetti, Antonio Saracino and Guido Incerti Cushion of Silene acaulis hosting a suite of beneficiary species in the Apennine mountains (Italy).

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    Historically, the struggle for resources and predation by herbivores were thought to be the main processes controlling the number and abundance of different species in plant communities. But in recent years evidence that some species can help other plants under harsh environmental conditions has become prominent. Such facilitative effects have been observed worldwide in deserts, wetlands, grasslands and scrublands, where nurse species facilitate beneficiary plants by buffering extreme temperatures, reducing exposure to solar radiation by shading, protecting palatable species from grazing, and increasing soil moisture and nutrient availability.

    In alpine environments, where plants face extreme weather conditions, cushion-shaped plants, thanks to their low stature and compact structure, are among the organisms best adapted to the critical combination of low temperatures, strong winds and severe desiccation. Several studies have reported that alpine cushion plants act as nurses, hosting a suite of stress-tolerant species within their canopy, where warmer, more protected and stable conditions occur. Among alpine cushion plants, Silene acaulis is well known as a nurse plant, and here we explore whether it always has a positive influence on coexisting species by analysing plant responses along an altitudinal severity gradient ranging from ~2,000 to ~2,800 m in the Italian Apennine mountains. We found that the ability of Silene to facilitate other plants considerably shifts along the gradient, being greatest at the intermediate elevation. On the other hand, cushion morphology dramatically changes with altitude, being lax, soft, and flat-shaped at low elevation and tightly knit and dome-shaped at high elevation. Silene compactness progressively increases with elevation because the plant stems are progressively more closely paired, likely to avoid heat dissipation. We discovered that cushions effectively act as heat traps only at medium and high elevations, while at lower altitude the soft flat cushions avoid excessive heat accumulation that may damage plant functions. However, at the upper end of the gradient, cushion compactness is so high that space available for hosting other species is greatly reduced, thus outweighing the positive heating effect for other plants.

    Image caption: Cushion of Silene acaulis hosting a suite of beneficiary species in the Apennine mountains (Italy).
    You can read the article in full here.

     

    Agricultural stressors affect stream ecosystems in unexpected ways

    Andreas Bruder, Romana K. Salis, Nicola J. McHugh and Christoph D. MatthaeiThe experimental set-up on the banks of a New Zealand stream. The insert shows a close-up of a channel simulating a stream ecosystem after colonisation by river organisms. Photo credit: P. Schenker.

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    Streams draining agricultural land are affected by many stressors caused by human land use, including water diversion for irrigation and elevated levels of nutrients from fertilizers, agrochemicals and deposited fine sediment. These stressors can interact, which makes their combined effect hard to predict based on the individual stressor effects. Such situations complicate management and restoration of agricultural streams. Our study addresses this challenge in an experiment conducted in New Zealand where agriculture has been rapidly intensifying. We used model stream ecosystems created in 128 small circular channels, which were subjected to the four stressors mentioned above. Channels were supplied continuously with water from a nearby river, enabling their colonisation by river invertebrates, algae and microorganisms. We studied stressor effects on decomposition of leaf litter from two tree species common alongside stream banks in New Zealand, evergreen mahoe and deciduous birch. Leaf litter is an important source of energy and nutrients for stream food webs, and one group of organisms that specialises in utilizing leaf litter as a resource are microscopic fungi.

    Reduced flow velocity (a consequence of streamwater diversion for irrigation) had the strongest negative effects of the stressors tested. It reduced the growth of fungi on both leaf species and slowed down leaf decomposition. Slower flow velocity curtails the supply of dissolved oxygen and nutrients from the streamwater to the fungi, which depend on these chemicals for growth. Deposited fine sediment also had strong effects, slowing down birch decomposition but accelerating mahoe decomposition. For birch, the effects of sediment addition and flow reduction caused stronger combined effects than one would have expected based on the individual effects of each stressor. Effects of elevated levels of nutrients and agrochemicals were relatively rare and subtle.

    These findings are both novel and important. The two stressors with the strongest impacts, flow reduction and deposited fine sediment, are considered less often in river management and restoration projects than nutrients or agrochemicals, and their interactions are rarely assessed. Finally, the contrasting stressor effects on mahoe and birch leaves show that stream ecosystem responses to agricultural stressors depend on the composition of the stream-bank vegetation.

    Image caption: The experimental set-up on the banks of a New Zealand stream. The insert shows a close-up of a channel simulating a stream ecosystem after colonisation by river organisms. Photo credit: P. Schenker.
    You can read the article in full here.

     

    Biotic and abiotic interactions, but not plant chemistry alone, contribute to chemical identity of invaded soils

    Vidya Suseela, Peter Alpert Cindy H. Nakatsu, Arthur Armstrong and Nishanth TharayilJapanese knotweed encroaching into an old-field in Massachusetts.

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    Spread of introduced, invasive plants can alter soil chemistry and microbial communities, and thus impact native ecosystem processes including nutrient cycling and soil carbon storage. Influence of some of these exotic species on native ecosystems could linger even after the removal of the invasive, contributing to a legacy effect. However the attributes of invasive plants that facilitate the creation and persistence of the new ecosystem properties is poorly understood. Discovering the mechanisms for this effect could help show why some introduced plants are more invasive than others and suggest how to restore invaded communities. Phenolic compounds, due to their abundance, persistence and biological activity, could be one of the more important classes of compounds that contribute to the lasting impact of plant identity on the chemistry of soil carbon in invaded soils. Despite this likely influence of plant inputs on invaded ecosystems, our knowledge of the significance of plant inputs in changing plant-soil feedbacks remains fragmentary.

    To address this knowledge-gap we investigated the changes in composition of phenolic compounds and microbial functional activities in soils following the invasion of Japanese knotweed (Polygonum cuspidatum; Fallopia japonia) in four sites across eastern US. Soils under knotweed stands were twice as rich in phenolic compounds compared to soils under native vegetation. Also, the invaded soil across the wider geographic region were more similar in soil phenolic profile and microbial communities compared to soils under and adjacent to knotweed stands at the same site. However, the composition of phenolic compounds in invaded soil had low resemblance to phenolics found in knotweed tissues, indicating a potential role for microbial metabolism and abiotic transformations in shaping the chemical identity of invaded soils. Knotweed influenced the chemistry not only of extractable phenolic compounds, but also of the non-extractable bulk soil carbon with a turnover rate of decades or more, suggesting a long-lasting influence of this invader in these ecosystems.

    Our results suggest that interactions between plant inputs, abiotic reactions, and biotic transformations could create and maintain new states in the soil that are chemically and biologically less diverse, and could outlive the invader themselves. Restoration could thus require not just removal of the species, but also post-removal interventions such as soil amendments.

    Image caption: Japanese knotweed encroaching into an old-field in Massachusetts.
    You can read the article in full here.

     

    Predation, food, and male-male competition drive natural variation in lizard tail autotomy

    Chi-Yun Kuo and Duncan J. IrschickSide-blotched lizard couple sharing a burrow. Photo credit: Chi-Yun Kuo.

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    Autotomy, or the voluntary shedding of body parts, is a behavior many animals (> 100 vertebrate and invertebrate families) use to survive predation. In some animals the detached body parts would continue moving to divert the attention of the predators away from the escaping animal. Autotomy is normally triggered by a force exerted on the discardable body part. In most cases the force comes from a predator but can sometimes be the result of male-male combats. Despite its benefit in enhancing the chance of survival in the field, autotomy imposes numerous short- and long-term costs, such as risk of infection, lower locomotor performance, lower mating success, and ultimately long-term survival. High costs of autotomy imply that selection should not take the use of this behavior lightly, and how easily autotomy occurs should reflect the underlying cost-benefit dynamics. Indeed, how easy it is to induce autotomy (i.e. the propensity for autotomy) exhibits remarkable variation among populations. In this study, we combined model simulations and field data to explicitly test the hypothesis that the ecological environment drives the variation in autotomy among populations. We first built a simple model to examine the roles of three major ecological factors: predation, food abundance, and male-male competition. Our predictions for the three factors are as follows: high predation and an abundance of food should favor high propensities for autotomy (i.e. easier to induce), as the former situation would increase the benefit of autotomy while the latter makes autotomy less expensive. On the contrary, more male-male fighting should favor lower propensities for autotomy because it is undesirable to lose body parts under non-life threatening situations. Simulation results confirmed all our predictions above. We then collected data on predation, food abundance, the intensity of male-male competition, and the propensity for tail autotomy from five side-blotched lizard populations in western U.S. With the ecological information, our model was able to predict how those five populations should vary in the propensity for tail autotomy. Again, our model successfully predicted the pattern of variation observed in the field, thereby providing further evidence that predation, food abundance, and male-male competition jointly drive natural variation in autotomy among populations.

    Image caption: Side-blotched lizard couple sharing a burrow. Photo credit: Chi-Yun Kuo.
    You can read the article in full here.

     

    Do non-native plants have the same traits at home? A comparison in France and New York

    J. Mason Heberling ,Thomas Kichey, Guillaume Decocq, and Jason D. FridleyCommon buckthorn on the forest edge in the native France (left) and invasive New York, USA (right). Photo by J.M. Heberling.

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    Non-native species become invasive when they actively spread in their introduced range. Trait comparisons between invasive and native species that occur in the same habitat have provided important explanations for how certain non-native species are so successful in their new range. However, it is unclear if these invasive species function similarly in their native range. In other words, do “invasive traits” arise after introduction or do some invasive species also display these traits in their native range?

    We compared leaf traits associated with plant function of two important forest invaders in their native (home) and introduced (invaded) ranges: black cherry, a tree native to the Eastern North America but invasive in Europe, and common buckthorn, a shrub native to Europe but invasive in Eastern North America. This transatlantic comparison was unique in that where one species is native the other is invasive, and vice-versa. Because the two species occur in the same regions, we could better control for the potential effect of regional conditions like climate to understand the effect of whether the species is invasive to the region.

    We found striking differences in leaf traits associated with plant strategy between native and invaded ranges for both species. Black cherry had similar rates of photosynthesis in the forests of native New York and invasive France, but leaves in France contained more carbon. Trait differences between home and invaded regions were more pronounced for common buckthorn, with 50-60% higher rates of photosynthesis in the invaded region (New York) compared to native France. Buckthorn leaves in New York also tended to have greater leaf nitrogen costs (an important nutrient for photosynthesis) and resorbed proportionately less of this nitrogen in autumn prior to dropping leaves. Autumn leaf nitrogen concentrations were 69% lower in France than New York. This trait might explain how buckthorn is able to drop its leaves later than other species in the invaded range.

    Overall, our study shows that traits, which together form a plant’s resource-use strategy, can be different between native and non-native ranges.

    Image caption: Common buckthorn on the forest edge in the native France (left) and invasive New York, USA (right). Photo by J.M. Heberling.
    You can read the article in full here.

     

    Comparing the decomposition of plant litter in aquatic and terrestrial ecosystems

    Pablo García-Palacios, Brendan G. McKie, I. Tanya Handa, André Frainer andStephan HättenschwilerLeaf litter layer in an Amazonian rainforest with fungi as key decomposer organisms. Photo credit: Stephan Hättenschwiler.

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    The decomposition of dead plant material, for example leaf litter, takes places in both terrestrial (for example, forest floors) and aquatic (for example, forest streams) ecosystems. Litter decomposition is one of the main components of the global carbon cycle and plays a fundamental role in soil fertility. Despite being one of the most studied ecological processes, litter decomposition has traditionally been approached independently by terrestrial and stream ecologists. Thus, although we have a pretty good idea about the main drivers of litter decomposition, we lack an understanding of the commonalities that may exist between aquatic and terrestrial ecosystems, and whether those drivers operate similarly under different climates such as tropical or Mediterranean.

    We analyzed data from an existing global litter decomposition experiment conducted in two ecosystems (forest floors and streams) across five climates (tropical, Mediterranean, temperate, subarctic and boreal). Litter from 15 different tree species combinations, originating from each climate, was incubated in the field inside custom-made mesh microcosms. The litter-filled microcosms were placed in direct contact with the soil surface (terrestrial) or submerged (aquatic) to simulate natural conditions. Three different mesh-sizes were used to limit the access of different components of the decomposer community to the litter inside the microcosms: fine (microbes), intermediate (microbes + mesofauna) and coarse (microbes + mesofauna + macrofauna). By doing so, we could test the contribution of different decomposer communities to the decomposition process.

    The most important result we found is that many commonalities exist between forest floors and streams at a global scale. For example, the initial litter concentration of little-studied micronutrients such as magnesium and calcium played a major role in litter decomposition in both ecosystems. In addition, the relative importance of decomposer organisms for litter decomposition was larger in streams than in forest floors.

    Our results can be used to improve global models developed to predict the effects of climate change on the carbon cycle. A useful approach would be to incorporate the global similarities found between aquatic and terrestrial ecosystems.

    Image caption: Leaf litter layer in an Amazonian rainforest with fungi as key decomposer organisms. Photo credit: Stephan Hättenschwiler.
    You can read the article in full here.

     

    Cold hardiness does not limit range shifts of Mediterranean pines to Central and Western Europe

    Christoph Bachofen, Thomas Wohlgemuth, Jaboury Ghazoul and Barbara MoserPinus nigra seedlings growing in the common garden in the Central Alps. Photograph by Christoph Bachofen.

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    Mediterranean tree species are adapted to long dry periods during summer, thus they might be well adapted to drought spells, which are projected to increase in Central Europe if climatic conditions become warmer and dryer. Frost, on the other hand, is an important factor limiting the distribution ranges of many tree species. It causes damage to buds and needles during winter and spring. Species distribution models predicting latitudinal range shifts might underestimate the risk from freezing damage, because they rely on average climate data and knowledge of the loss of cold hardiness from winter to spring, called dehardening, is sparse for many tree species.

    We estimated the vulnerability of Mediterranean pines to winter and spring frost, and thus their potential to migrate northwards, by comparing the cold hardiness of Mediterranean populations of Pinus sylvestris (Scots pine), Pinus nigra (black pine) and Pinus halepensis (Aleppo pine) to Central Alpine populations of P. sylvestris. Seedlings were grown in a common garden in a cold Central Alpine valley. We artificially froze needles of every species and population at several temperatures on seven dates between February and July 2013. Cold hardiness was determined by estimating the temperature at which the majority of the needles were injured. Needle injury was measured in terms of the amount of electrolytes leaking from the ruptured needle cells.

    We found no difference between the cold hardiness of Mediterranean P. sylvestris and P. nigra and Central Alpine P. sylvestris. The cold hardiness was not related to the temperature at the seed origin of the populations. All populations of P. sylvestris and P. nigra maintained extremely wide safety margins against frost, which exceed that of deciduous trees considerably. P. halepensis, on the other hand, exhibited a very narrow safety margin until late spring and its cold hardiness was in the range of temperatures that regularly recur in Central Europe in winter.

    Our study shows that Mediterranean P. sylvestris and P. nigra populations are equally well adapted to the late winters and spring frosts of Central Europe as P. sylvestris from the Central Alps. P. halepensis might be resistant to winter temperatures occurring in the Atlantic region of Europe but not to current frost events in Central Europe.

    Image caption: Pinus nigra seedlings growing in the common garden in the Central Alps. Photograph by Christoph Bachofen.
    You can read the article in full here.

     

    Additive genetic variance and effects of inbreeding, sex and age on heterophil to lymphocyte ratio in song sparrows

    Sylvain Losdat, Peter Arcese, Laura Sampson, Nacho Villar, Jane M. ReidSong Sparrow. Image provided by authors.

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    An individual’s ability to survive and reproduce, defined as individual fitness, can be predicted and influenced by physiological traits such as the amount of stress the individual experiences. As a consequence, individual stress has been hypothesized to influence the evolution of life-history traits and strategies. However, the hypothesis that variation in physiological traits could influence life-history evolution requires that such traits can be genetically inherited. Yet, the genetic and environmental determinants of individual physiological traits linked to stress remain relatively unknown, particularly in vertebrates under natural environmental conditions.

    We used long-term data from a study on wild song sparrows in Western Canada to quantify genetic variation in the ratio between heterophils and lymphocytes, which are blood cells with an immune function. The heterophil to lymphocyte (H:L) ratio is a physiological metric that reflects individual stress. We collected and analysed blood samples from 350 fully developed individuals for which we have a complete genetic pedigree. We subsequently estimated the effect of individual coefficient of inbreeding on H:L ratio to test whether being inbred was influencing individual stress. We also tested the effect of sampling period, age and sex. Last, we estimated the magnitude of genetic inheritance of H:L ratio using the genetic pedigree.

    Overall, H:L ratio increased with individual coefficient of inbreeding, indicating that more inbred individuals have higher stress levels. This implies that individuals that mate with closer relatives could produce offspring with relatively high individual stress, which might in turn impact their offspring’s survival and reproductive success. Additionally, H:L ratio was higher in older individuals, but did not differ between males and females.

    The estimated genetic inheritance of H:L ratio was small (h2=0.04) and did not differ significantly from zero, suggesting that individual stress is primarily influenced by environmental factors rather that being genetically inherited from parents. This low genetic inheritance suggests that individual stress has low potential to evolve because any advantage will not be transmitted to the new generation.

    Image caption: Song Sparrow. Image provided by authors.
    You can read the article in full here.

     

    Fewer new species colonize at low frequency N addition in a temperate grassland

    Yunhai Zhang, Carly J. Stevens, Xiaotao Lü, Nianpeng He, Jianhui Huang, Xingguo HanYunhai Zhang worked in the field for simulation wet nitrogen deposition.

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    Increasing availability of biologically-active nitrogen (N), from either human fertilization or atmospheric deposition, has caused biodiversity loss in diverse ecosystems . Based on a field study that independently manipulated the rates and frequencies of N inputs in a temperate grassland in Inner Mongolia, China (photographed by Wei Liu), we were able to test the responses of ecological processes to the frequency and rate of N addition. Because of the different frequencies of N added to ecosystems between fertilizer application and atmospheric deposition, traditional N addition experiments may have overestimated the effects of atmospheric N deposition on biodiversity loss, as it has been found that low frequency N additions, as used in traditional studies, lead to more rapid biodiversity loss. It remains unclear, however, whether new species colonization (gain) or old species extinction (loss) is the cause of such differences.

    In this study we explore both processes and demonstrate that there are changes in composition masked by considering species richness alone. We found that the gain of new species was higher at a high frequency of N addition than at a low addition frequency, whilst loss of existing species was similar at the two frequencies of N addition. The number of species gained decreased and species lost increased with increasing rate of N addition at both annual and five-year intervals. Cumulative gain of new species was negatively correlated with soil acidification, ammonium concentration and community biomass accumulation, whereas cumulative loss of old species was positively correlated with these variables.

    Our findings indicate lower new species gain rather than higher old species loss accounted for the lower species richness at low frequency of N addition. Given the lower new species colonization at low frequency of N addition, previous N fertilization experiments may have overestimated the effects of N deposition on biodiversity loss via understatement of the capacity for new species colonization. Moreover, our study suggests that practices that prevent soil acidification and ammonium accumulation, or remove biomass (such as grazing or mowing), may decrease the rate of biodiversity loss under N enrichment via fertilization or atmospheric deposition.

    Image caption: Yunhai Zhang worked in the field for simulation wet nitrogen deposition.
    You can read the article in full here.

     

    Environmental cue to germinate in gaps is closely associated with seed sizes

    Qingqing Xia, Mariko Ando and Kenji SeiwaSeed germination experiment in a plant growth chamber in which we provided a R: FR ratio by stick-type light-emitting diode lamps.

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    It is well known that seeds of pioneer species use either temperature fluctuations or spectral composition of light as gap detection signals. The relative importance of these two signals, however, remains unknown due to the lack of germination experiments testing the interactive effects of the different signals. We hypothesized that the relative importance of these two factors differs among species with different seed sizes, because the environmental signals may change with soil depth in different manner.

    We monitored changes in these environmental signals at different soil and litter depths in forest gaps and under adjacent forest understorey. We also conducted a seed germination experiment in darkness and under red to far-red (R: FR) light ratios of 0.1, 0.4, and 1.0 under fluctuating (30/10 °C day/night) and constant (20 °C) temperatures using 10 pioneer tree species with different seed sizes.

    In forest gaps, light is a germination cue that is detectable only at the soil surface or immediately below it when litter is absent, whereas temperature signals can be detected in deeper soil. The proportion of seeds germinating in small-seeded species (seed mass ≤1.05 mg) was strongly promoted by higher R: FR ratios, thereby ensuring germination of seeds buried close to the soil or litter surface. In contrast, percent germination of large-seeded species (seed mass ≥200 mg) was strongly facilitated by temperature fluctuations, ensuring germination of seeds even if buried in deeper soil and litter. In three medium-seeded species (2.84–9.50 mg), interactive effects of the two signals were observed.

    Our results suggest that in temperate pioneer trees, differences in seed size across species were associated with differences in the relative importance of light vs. temperature regimes as germination cues for gap detection.

    Image caption: Seed germination experiment in a plant growth chamber in which we provided a R: FR ratio by stick-type light-emitting diode lamps.
    You can read the article in full here.

     

    Dung beetles reduce drought stress in plants without increasing plant susceptibility to an aboveground herbivore

    Scott N. Johnson, Goran Lopaticki, Kirk Barnett, Sarah L. Facey, Jeff R. Powell and Susan E. Hartley Rain exclusion shelters at the DRI-GRASS research platform.

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    It’s reckoned that insects provide well in excess of USD $500 billion of ecosystem services to mankind every year in the form of pollination and pest control. Some of the most important providers, however, have the less glamorous role of consuming animal faeces – the dung beetles. There are over 6,000 species of dung beetle living on all continents except Antarctica. These beetles provide ecological functions and services by virtue of their physical manipulation of the ecosystem, making them miniature ecosystem engineers. In addition to consuming animal dung, these engineers disperse and incorporate it into the soil via burrowing activity. This drives a number of ecological processes including nutrient cycling, soil aeration, seed burial and parasite suppression. This is estimated to contribute an amazing USD $380 million in ecosystem services to the US cattle industry alone. We were interested in whether these ecosystem services might help mitigate the negative impacts of climate change, particularly altered rainfall patterns, on plant growth and productivity.

    Using rain exclusion shelters in SE Australia, we tested how dung beetles (Bubas bison) might alleviate the negative impacts of drought on plants (Brassica oleracea) by enhancing soil water retention. Provisioning plants with resources, however, might make them more nutritious for herbivores and potentially cancel out any benefits that dung beetles conferred, so we also tested whether plant suitability to a herbivorous pest (Plutella xylostella) changed when dung beetles were present. We found that dung beetles increased soil water retention by 10% and increased plant growth by almost three fold under drought conditions. Dung beetles also allowed plants to capture more nutrients such as nitrogen and carbon. Contrary to our predictions, however, dung beetles did not make the plants more susceptible to the herbivore, potentially because they increased nutrient content but not the concentration in leaves. These results point to a potential beneficial role for insect ecosystem engineers in climate change adaptation and crop protection.

    Image caption: Rain exclusion shelters at the DRI-GRASS research platform.
    You can read the article in full here.

     

    Seasonal changes in temperature and bush lupine availability drive bordered plant bug abundance

    Christopher A. Johnson, Renato M. Coutinho, Erin Berlin, Kimberly E. Dolphin, Johanna Heyer, Britney Kim, Alice Leung, Jamie Lou Sabellon, and Priyanga Amarasekare Left photo: Our field site in Santa Barbara County, CA, with bush lupine. Right photo: adult bordered plant bugs on bush lupine in the laboratory; note the yellow egg cluster on the bottom-right and adults preparing to mate on the top-left. Photo credits: Christopher A. Johnson

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    Studying species’ population dynamics (how population abundances change over time) is important for understanding how species persist in variable environments as well as predicting which species may be vulnerable to extinction due to climate change. Both biological factors, such as food availability, and non-biological factors, such as temperature, may be important drivers of population dynamics.

    Mathematical models are useful tools for ecologists to study population dynamics because models can simultaneously consider the effects of multiple factors and generate predictions that can be tested using experiments or empirical data. Models are powerful tools because they can investigate which processes are likely to be important and make predictions that may be otherwise impossible. It is critical to develop models using real-world “study systems”, which guide and validate models.

    We noticed a striking pattern in the abundance of the bordered plant bug in coastal Santa Barbara Co., California (left photo): juveniles and adults are completely absent during certain times of the year and extremely abundant during others. Because plant bugs are ectotherms (species that depend on external heat sources) and primarily eat bush lupine, which drops its leaves in winter, we hypothesized that plant bug population dynamics are driven by seasonal changes in temperature and food availability.

    To investigate how plant bug populations respond to changes in temperature and food availability, we raised plant bugs in the laboratory (right photo) at four temperatures and measured their birth, development, and death rates. We then developed a model using the laboratory data, and then varied temperature and food availability as observed in nature. The model predicts similar population dynamics to our field data only when it includes both temperature and food availability; thus, plant bug population dynamics are likely driven by both seasonal changes in temperature and bush lupine availability.

    More broadly, this study is important because it provides a mathematical framework, validated using the bordered plant bug, that can investigate ectotherm population dynamics and predict which species may be vulnerable to extinction due to atypical changes in temperature or food sources under climate change.

    Image caption: Left photo: Our field site in Santa Barbara County, CA, with bush lupine. Right photo: adult bordered plant bugs on bush lupine in the laboratory; note the yellow egg cluster on the bottom-right and adults preparing to mate on the top-left. Photo credits: Christopher A. Johnson.
    You can read the article in full here.

     

    Liverworts to the rescue: an investigation of their efficacy as mycorrhizal inoculum for vascular plants

    Jill Kowal, Silvia Pressel, Jeffrey G. Duckett, and Martin I. Bidartondo Septate hyphae emanating from a microscopic leafy liverwort rhizoid following resynthesis with the ericoid mycorrhizal fungus isolate.

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    Healthy plant life aboveground is largely dependent on the function of belowground fungal communities. Mycorrhizal fungi are ubiquitous in the soil, forming mutualistic plant-fungal interactions in all terrestrial ecosystems. Mycorrhizal fungi are not transmitted directly from parent to offspring plants, so mycorrhizal mutualisms must form de novo when plants establish from seed.

    A widespread mycorrhiza-forming fungus (Pezoloma ericae (D.J. Read) Baral) associates with plants in the order Ericales and also forms mutualistic associations with several families of liverworts, many of which are also widespread throughout the world. The ecological significance of this ‘shared’ mycorrhizal partnership remains largely unknown. The Ericales number approximately 8,000 species and include familiar plants such as heathers, blueberries and cranberries.

    We investigated the functional associations among ericaceous plants, liverworts and mycorrhizal fungi in wet lowland heathland dominated by heathers, a top priority habitat for conservation. The research aimed to determine whether pioneering liverwort plants harbouring P. ericae can act as inoculum for the re-establishment of heather plants and can therefore be proposed as a practical application in heathland restoration ecology. The process of becoming mycorrhizal can be limiting to plant establishment in ecosystems poor in nutrients, such as heathlands.

    Our molecular analyses confirmed that the liverworts and heather (Erica tetralix and Calluna vulgaris) share the same mycorrhizal fungus, P. ericae. We cultured liverworts from spores, and introduced the P. ericae isolate. Within weeks, the liverworts were colonized by the fungus, as found in nature. These liverworts were then planted together with heathers (both seedlings and cuttings) in field-simulating conditions, to assess the functional role of the colonized liverworts on the heathland plants. Germination, rooting success, plant survival, and growth were measured after several weeks and months.

    Our research showed, for the first time through molecular identification, that British species of leafy liverworts harbour a fungus that forms mycorrhizas with vascular plants. We unequivocally demonstrated that these fungal symbionts emanate from leafy liverwort rhizoids and repeatedly colonize roots forming typical "ericoid mycorrhizas" in seedlings and cuttings. Plant establishment is significantly more successful when plants are co-planted with liverworts containing these fungi. Growth is significantly increased as well, but can be initially suppressed – there may be an initial cost to partnering with fungi.

    The liverworts tested are adaptable to considerable swings in temperature and moisture levels in nature, and are relatively easy to cultivate and apply for inoculation treatments. We therefore conclude these liverworts are a viable inoculum delivery mechanism for heather establishment, and preferable to a slurry of the fungus isolate or other Ericaceae plants as they are more cost effective and practical on a large scale. We plan to test this inoculum in nature now that we have established its efficacy in our experiments.

    Image caption: Septate hyphae emanating from a microscopic leafy liverwort rhizoid following resynthesis with the ericoid mycorrhizal fungus isolate.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Old birds become worn and rusty too

    Katherine A. Herborn, Francis Daunt, Britt J. Heidinger, Hanna M. V. Granroth-Wilding, Sarah J. Burthe, Mark A. Newell and Pat MonaghanFamily of Isle of May shags, Phalacrocorx aristotelis. ©Lucie Bernardova.

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    While we know that our own bodies deteriorate as we get older, relatively little is known about these processes in wild animal populations. Much of what we know about aging in other species comes from research on species with relatively short lifespans, such as insects and rodents, which can be studied from birth to death in laboratories. To determine whether the same patterns of aging occur in long lived organisms requires long term programmes and long scientific careers. Moreover, understanding aging under natural conditions, instead of in the relatively homogenous and safe laboratory environment, presents the additional challenge of finding the same animal at different stages of its life in the wild. One reason why individuals deteriorate with age is thought to be akin to rusting – that is accumulated oxidative damage to tissues. The term ‘oxidative stress’ describes a state where oxidising molecules, which are mostly a natural by-product of metabolism, exceed the body’s level of antioxidant defences, and thus are free to react with and damage body tissue. We examined age-related changes in oxidative stress exposure in the Isle of May population of a long-lived seabird, the European Shag (Phalacrocorax aristotelis). Chicks were given unique coloured and lettered leg rings, allowing them to be recognised throughout their lives. Over three consecutive breeding seasons, we collected tiny blood samples from individuals aged from 2 to 22 years at the start of the study. Individuals of all ages showed an increase in oxidative stress exposure from one year to the next, and those with the highest levels were more likely to die. This is consistent with the expectation that older individuals will invest less energy and resources into self-maintenance in favour of more investment into reproduction, as a last ditch attempt at passing on their genes. Our study, therefore, provides a rare insight into the process of aging in a long-lived species; they become rusty much like ourselves.

    Image caption: Family of Isle of May shags, Phalacrocorx aristotelis. ©Lucie Bernardova.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Functional replacement across species pools of vertebrate scavengers separated at a continental scale maintains an ecosystem function

    Chantal M. Huijbers, Thomas A. Schlacher, Rosemary R. McVeigh, David S. Schoeman, Andrew D. Olds, Marion B. Brown, Kasun B. Ekanayake, Michael A. Weston and Rod M. Connolly Removal of fish carcasses from ocean beaches, a key ecological function, is maintained across a continental scale via functional species replacement: scavenger assemblages on tropical beaches were dominated by raptors, such as white-bellied sea eagles (left image), and substantially different from temperate scavenger assemblages, which were dominated by red foxes (right image). Photographs taken while scavengers were actively removing beach carrion during the experiments. Credits: C. Huijbers.

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    The composition of the total variety of species available to colonise a particular site (the ‘species pool’), and those that actually occur together (the local assemblage), often show large geographical variation, reflected in distinct ‘faunas’ and ‘bio-regions’ across the globe. Whilst such structural differences are often prominent, much less is known about whether these geographic patterns in species identity change the functioning of ecosystems.

    Scavenging, the consumption of animal carcasses, is an important ecological function. We tested how differences in the composition of local scavenger assemblages affect the removal rates of carrion (dead fish) from sandy beaches. We deployed fish carcasses on beaches in tropical north Australia and temperate south Australia and used motion-triggered cameras to monitor which animals scavenge on the carcasses.

    Tropical assemblages of vertebrate beach scavengers were dominated by raptors such as brahminy kites and white-bellied sea eagles, while carrion on temperate beaches was mostly removed by invasive red foxes. Despite the distinct differences in terms of which species make up the scavenger assemblages, the rates at which carrion was removed from beaches was similar between regions separated by thousands of kilometres. This indicates that two very distinct species assemblages can maintain a pivotal ecological process via functional replacement of species.

    Image caption: Removal of fish carcasses from ocean beaches, a key ecological function, is maintained across a continental scale via functional species replacement: scavenger assemblages on tropical beaches were dominated by raptors, such as white-bellied sea eagles (left image), and substantially different from temperate scavenger assemblages, which were dominated by red foxes (right image). Photographs taken while scavengers were actively removing beach carrion during the experiments. Credits: C. Huijbers.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Re-growing a tropical dry forest: functional plant trait composition and community assembly during succession

    Vanessa Buzzard, Catherine M. Hulshof, Trevor Birt, Cyrille Violle and Brian J. EnquistRecently disturbed TDF in Sector Santa Rosa of Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. Photo credited to Catherine Hulshof.

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    Most of the world’s remaining tropical forests have experienced some degree of disturbance. Tropical dry forests (TDFs), which are characterized by seasonal drought, currently occupy 42% of all forested tropical regions throughout the world but today less than 2% of TDFs throughout Central America remain undisturbed. The primary conversion of this forest type is a result of a long history of human land use. In order to restore these tropical ecosystems, ecological studies are needed to help understand how the structure and function of these forests change over time.

    Ecological theory suggests that the environmental conditions following disturbance are stressful. Therefore, directly following a disturbance, communities are likely to be characterized by drier and more variable soil moisture, higher light levels, increased temperatures, and lower relative humidity acting as a filter where only a few species can successfully establish. Over time, as environmental conditions improve, more species establish and begin to compete with one another for resources resulting in greater differences between species. This shift in resource availability and turnover in species composition through time has been the primary focus of successional ecology for many years, resulting in little understanding of the change in function over time. Therefore, in this study we take a more mechanistic approach to assess community function over time by measuring physiological and chemical traits of leaves that are related to the success of an individual (functional traits) for woody plants within 14 plots that have varying times since disturbance.

    When we compare species composition and community function, we find that older TDF communities differed significantly from younger forests in species composition, above ground biomass and functional traits. The observed trait shifts appear to be primarily determined by a concomitant shift in resource availability, e.g., water availability (reflected in increased soil moisture) and light availability. Further, early stages of succession were uniformly characterized by traits related to strategies important for avoiding water loss, whereas in later successional stages traits reflected increased water and nutrient availability. Interestingly, in contrast to expectations, functional trait variation did not generally change through succession. Our results suggest that regenerating TDFs are resilient and can be restored within a human lifetime.

    Image caption: Recently disturbed TDF in Sector Santa Rosa of Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. Photo credited to Catherine Hulshof.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Visual ecology of Eulemur suggests a cathemeral origin for the primate cone opsin polymorphism

    Kim Valenta, Melissa Edwards, Radoniaina R. Rafaliarison, Steig E. Johnson, Sheila M. Holmes, Kevin A. Brown, Nathaniel J. Dominy, Shawn M. Lehman, Esteban J. Parra, Amanda D. Melin A brown lemur (Eulemur fulvus) searches for fruits under daylight conditions in Ankarafantsika National Park, Madagascar. Photo credit: Travis Steffens.

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    Unlike most primates, which are predominantly active during either the day or night, lemurs in the genus Eulemur are active across the 24-hour daily cycle. Although debated, recent evidence suggests that this activity pattern has a long evolutionary history for these lemurs, and was possessed by their ancestors. The impact of nighttime vs. daytime activity on the evolution of color vision in primates is actively debated and we explore the visual ecology of lemurs that are active at both times to shed new light on this debate. We studied three groups of wild brown lemurs (Eulemur fulvus) in Ankarafantsika National Park, Madagascar and collected stool samples for DNA analysis to study the opsin genes underlying color vision. We measured the color and brightness of dietary fruits and modeled the conspicuousness of food objects to different color vision types under daylight, twilight, and moonlight conditions. We found the color vision of E. fulvus to be routinely dichromatic – all males and females had the same color vision, consisting of two color channels. Our models suggest that dichromacy is well-suited to the foraging ecology of this species. The color vision of E. fulvus differs from its close relative E. flavifrons, for which polymorphic trichromacy – the addition of a third (red-green) color channel in some females - has been reported. We suggest that ecological differences between species of Eulemur could reveal thresholds for the origins of polymorphic trichromacy, which preceded the evolution of routine trichromatic vision in humans and other primates.

    Image caption: A brown lemur (Eulemur fulvus) searches for fruits under daylight conditions in Ankarafantsika National Park, Madagascar. Photo credit: Travis Steffens.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Food as fuel: How food protein-carbohydrate content affects resting metabolic rates

    Rebecca M. Clark, Anthony J. Zera, and Spencer T. BehmerFemale cricket housed in a flow-through respirometry chamber used to measure carbon dioxide production and oxygen consumption.  Photo by S.T. Behmer.

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    Metabolic rate is a fundamental physiological characteristic of animals that summarizes overall energy usage by an organism. Because of its central role in organismal physiology, metabolic rate is widely thought to be influenced by external and internal factors, especially food nutrient content and physiological state (e.g. reproductive status). However, despite decades of study in the context of nutritional ecology and life-history evolution, the effects of food nutrient content and animal reproductive status on resting metabolic rates are poorly understood.

    We tested how the balance and concentration of protein and carbohydrate in food affected resting metabolic rate in females of the sand cricket, Gryllus firmus. Females of this species occur in two physiologically distinct forms (morphs) that specialize in either flight ability or egg production. Because these forms differ dramatically in many aspects of fat and amino acid metabolism related to production of fat flight fuel and eggs, we also expected them to differ in metabolic rate. Surprisingly, we found that the dramatic differences in organismal biochemistry did not lead to differences in resting metabolic rates between the morphs. Likewise, resting metabolism was similar across diets, even though the diets had different protein-carbohydrate profiles. The maintenance of constant resting metabolic rate on different diets occurred because crickets shifted the nutrients that they used as metabolic “fuel,” to compensate for changes in the amount and ratio of protein and carbohydrate in their diet.

    Therefore, counter to expectations, individuals can experience dramatic variation in nutrient input and have vastly different physiological characteristics, without showing any signs of these major distinctions at the level of whole-body resting metabolic rate. Conversely, the absence of differences among individuals in resting metabolic rate does not necessarily mean that those individuals do not differ dramatically in underlying aspects of biochemical function. Physiological studies need to be undertaken both at the whole-organism and biochemical levels to identify adaptive biochemical differences among individuals and to determine the extent to which these differences give rise to differences in overall energy usage.

    Image caption: Female cricket housed in a flow-through respirometry chamber used to measure carbon dioxide production and oxygen consumption. Photo by S.T. Behmer.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Trade-offs in juvenile growth potential vs. shade tolerance among subtropical rainforest trees on soils of contrasting fertility

    Kerrie M. Sendall, Christopher H. Lusk and Peter B. ReichPhoto provided by authors.

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    Coexistence of tree species is often associated with a trade-off between juvenile shade tolerance and growth rate in gaps. On the other hand, species sorting along/across soil fertility gradients is thought to involve trade-offs between the nutrient and carbon economies of plants. Little is known, however, about how these two types of trade-off interact. We asked if the growth versus shade tolerance trade-off in Australian subtropical rainforest is influenced by soil phosphorus (P) availability, and if similar trade-offs occur on P-rich basalt and low-P rhyolite.

    We measured growth of juveniles (400-1200 mm tall) of 15 common tree species across a wide range of light intensity in an Australian subtropical rainforest. Nine common species were measured on the basaltic soil and seven on the rhyolitic soil; one species occurred on both soils. We used hemispherical photographs to quantify light environments above each plant. We then used relationships of growth with light to compare growth of each species at 3, 6, 12, and 20% light availability, and to calculate two measures of species’ light requirements: (a) the light compensation point (the light level at which stem growth averages zero) and (b) the minimum light requirement (the bottom 5% of the range of light environments occupied by each species).

    Growth in 3 and 6% light was negatively related to minimum light requirements, but positively related at 20% light. Similar growth versus shade tolerance trade-offs were found among species adapted to the two different substrates. However, the species growing on P-rich basalt encompassed a wider range of light compensation points and growth rates than species growing on low-P rhyolite.

    Our results suggest that differential adaptation to soil P availability has little effect on the relationship between shade tolerance and maximum growth rates. However, they do suggest an effect on functional diversity: both the fastest-growing species and the most shade-tolerant species are limited to P-rich soils.

    Image caption: Photo provided by authors.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Colour pattern mimicry in flowers- the functional importance of complex floral colour pattern in a food-deceptive orchid

    Xiaokai Ma, Jun Shi, Hans Banziger, Yangna Sun, Yanyan Guo, Zhongjian Liu, Steven D. Johnson and Yibo Luo Mimic (silver slipper orchid Paphiopedilum micranthum, centre) and its co-occurring food flowers on a background of their habitat, framed in bee hexagonal vision.  Image courtesy of Xiaokai Ma.

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    Mimicry, where one species evolves to resemble another, unrelated species, is a renowned textbook example of natural selection and adaptation. Mimicry is often based on imitation of special visual patterns, such as the gorgeous colour patterns on wings of butterflies and body surface of snakes. Flower mimics, which are widespread among plants, often dupe animal pollinators by providing no reward (i.e. nectar), but imitating the colour of nectar-providing flowers that share the same habitat. Moreover, both the mimics and the food flowers often display complex colour patterns, including contrast between outer and central flower parts, that could be discriminated by pollinators.

    To detect whether the colour pattern is the key to flower mimicry, we tested the effects of floral colour patterns in the silver slipper orchid, Paphiopedilum micranthum, on pollinator bumblebee choices and pollination success using behavioural tests in a community context. Using a bee vision model and evolutionary analysis, we also compared the colour patterns of the orchid with those of its relatives, and the food flowers that it mimics.

    Our results reveal that orchid pollination success might be enhanced by colour patterns that mimic those of food flowers in the local community. Such mimicry enhances attraction of the orchid to bumblebees. Experimental disruption of the colour pattern clearly hampers decision-making by bumblebees, and this decreases pollination success of the orchid. Evolutionary analysis indicate that the colour pattern of orchid mimics might have been shaped by multiple evolutionary histories, including evolutionary innovation of the outer floral colour and a pre-adaptation of the ancestral centre floral colour.

    Our study is novel in its inclusion of colour pattern in the study of floral mimicry in the context of the associated plant community, and provides the first detailed evidence for the functional importance of colour pattern mimicry for a deceptive flower. This finding advances our understanding of the evolutionary processes governing floral deception via the functional significance of colour pattern traits that influence signalling efficacy. This highlights the importance of complex signals in facilitating species interactions.

    Image caption: Mimic (silver slipper orchid Paphiopedilum micranthum, centre) and its co-occurring food flowers on a background of their habitat, framed in bee hexagonal vision. Image courtesy of Xiaokai Ma.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

    Special Feature: The functional role of silicon in plant biology

    Molecular evolution of aquaporins and silicon influx in plants

    Rupesh Deshmukh and Richard R. BélangerHorsetail plant (Equisetum arvense) in the field (left). Scanning electron micrograph of horsetail leaf (top right) and X-ray microanalysis mapping of silicon presence (bottom right).

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    Silicon (Si) is one of the most abundant elements in the earth crust, but whether it is essential for plant growth remains a matter of debate. Plants take up Si through the roots in the form of silicic acid, and can accumulate concentrations as high as 10% on a dry weight basis. Nevertheless, most plants (with the notable exception of horsetail) can complete their life cycle without Si. For this reason, Si is not considered an essential element, in spite of the multiple studies that have shown its beneficial role for plants, especially under conditions of biotic and abiotic stress.

    The benefits plants derive from Si are well correlated with their ability to take up Si from the soil, and this ability varies greatly among plant species. In the context of better defining the ecological role of Si in plants, it thus becomes very important to understand which and how plant species can take up silicon.

    Si uptake in plants depends on two specific proteins, an influx transporter and an efflux transporter, both with unique characteristics. Recent studies suggest that the presence of an influx transporter is the indispensable key for a plant to be able to absorb Si. Based on DNA sequence analyses and comparisons, influx transporters appear to bear conserved features that allow us to classify plant species as Si-competent or not. While it is unclear how and why plants have acquired or lost this trait, genomic data now offer a reliable molecular tool to predict with accuracy which plant species are predisposed to benefit from Si. This work presents a detailed review of the molecular features inherent to Si influx in plants, a property that has a profound impact on Si biogeochemical cycling and the role of Si in many fundamental aspects of ecology.

    Image caption: Horsetail plant (Equisetum arvense) in the field (left). Scanning electron micrograph of horsetail leaf (top right) and X-ray microanalysis mapping of silicon presence (bottom right).
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    How do precipitation gradient and evolutionary history shape the variations in leaf and root traits in the Inner Mongolia grassland?

    Junhui Cheng, Pengfei Chu, Dima Chen and Yongfei BaiRoot systems of six grasses widely distributed in the Inner Mongolia grassland.

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    The attributes of leaves and roots are fundamental for understanding different strategies that plants use to acquire resources, like water, soil nutrients, and light, in different environmental conditions. This is important because these resource acquisition strategies are essential for species coexistence, community assembly and functioning of terrestrial ecosystems. Species with less dry matter investment per leaf area and root length have high growth rate but short life span, indicating a resource acquisitive strategy. In contrast, species with high dry matter investment per leaf area and root length have low growth rate but long life span, suggesting a resource conservative strategy. It has been assumed that variation in environmental factors (e.g. precipitation and temperature) and evolutionary history (species divergence time on the evolutionary tree) shape both leaf and root traits. The branching architecture of fine roots also affects the functional role of living roots, such as acquisition and transport of water and nutrients. However, few studies have examined the effects of evolutionary history and environmental gradients on species leaf and root traits, or considered how plants are able to access increasingly scarce resources like water and nutrients as climate shifts from relative moist to very arid?

    In this study, we examine how leaf and root traits vary across 55 species and 21 plant communities along a 2,000-km transect in the Inner Mongolia grassland, part of the largest contiguous grassland in the world, the Eurasia steppe. Our results suggest that acquisition of soil resources, such as water and nutrients, is a fundamental determinant of plant dry mass investment per root length in arid and semiarid grasslands. Across the transect, species that evolved relatively late tended to have high dry matter investment per leaf area and root length for the first root branching order, and were distributed in dry and infertile habitats, while earlier-evolving species exhibited low dry matter investment per leaf area and root length and were found in wet and fertile habitats. These findings provide new insights for predicting the response of species and ecosystems to changes in temperature and precipitation in arid and semiarid grasslands.

    Image caption: Root systems of six grasses widely distributed in the Inner Mongolia grassland.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Cold adaptation in insects involves adaptive modifications of the cell membrane phospholipid composition

    Stine Slotsbo, Jesper G. Sørensen, Martin Holmstrup, Vladimir Kostal, Vanessa Kellermann and Johannes OvergaardThis photo shows different fruit flies along a cold tolerance gradient, and how the phospholipid fatty acids in the membrane are expected to become more unsaturated with increasing cold tolerance. Photo provided by Heath A. MacMillan.

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    Maintaining function and structural integrity of cell membranes is central for the performance and survival of animals. Because temperature influences the physical properties and fluidity of animals’ biological membranes it is hypothesized that temperature stress may compromise membrane function. In accordance with this hypothesis it is often found that acquisition of thermal tolerance following acclimation involves modifications of the cell membrane lipid composition. Each membrane phospholipid consists of a head group attached to two fatty acids, and modification can be in type of head group, types of fatty acids, or a combination of these factors. Membrane modifications are associated with changes in the membranes' physical properties such that appropriate function is secured at the acclimation temperature. Parallel differences in membrane lipid composition have been found between species and between populations of insects that are adapted to different thermal environments. However, there are few large multi-species studies that investigate directly the interspecific association between membrane lipid composition and thermal tolerance in insects.

    Here we present the most comprehensive interspecific investigation of phospholipid fatty acids composition within insects (and cold-blooded animals in general). Using 57 species of fruit flies originating from both temperate, subtropical and tropical environments we found clear differences between species in phospholipid fatty acid composition. When we related these differences to species’ cold tolerance, which constitute a powerful proxy for their cold distribution limits, we found that phospholipid fatty acids could explain more than 20 % of the variation in cold tolerance found between species. Considering that a number of other important membrane parameters (phospholipid head group composition and concentration of sterols and other lipid components) were not measured, our finding highlights that phospholipid fatty acids and membrane adaptations in general play a highly significant role in thermal tolerance in insects.

    Image caption: This photo shows different fruit flies along a cold tolerance gradient, and how the phospholipid fatty acids in the membrane are expected to become more unsaturated with increasing cold tolerance. Photo provided by Heath A. MacMillan.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Macronutrients, weapons and genital traits in male broad horned beetles

    Clarissa M. House, Kim Jensen, James Rapkin, Sarah Lane, Kensuke Okada, David J. Hosken and John Hunt Male Gnatocerus cornutus fight using an enlarged mandible which is a secondary sexual trait. Photo credit: Matthew Silk.

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    The calorific content and the nutritional composition of food that is acquired from the environment is likely to be vitally important for individual survival, growth and morphology (i.e. the physical characteristics of an animal). This could be especially important if the nutritional requirements of traits differ, such that the optimization of one trait occurs at the expense of another, and therefore trade-offs occur due to nutrient imbalance in the diet that is consumed. In this study we used 24 well-defined, artificial diets to test the sensitivity of a flour beetle, Gnatocerus cornutus, to variation in the calorific content and ratio of two major nutrients, protein (P) and carbohydrates (C) consumed during larval development to adulthood. We found that extreme calorific restriction was fatal or slowed the rate of development. However, beyond a minimum amount of food, the ratio of consumed macronutrients was critically important for the size of the morphological traits that we measured. Male weapons grew most in response to the consumption of P and in particular C whereas the genitalia had the weakest response. Even though different traits grew at different rates the P:C ratio that maximized survival, development rate and the size of all morphological traits was 1:2. This shows that the balance of P:C in the diet that is optimal for survival also optimizes development rate and the size of all morphological traits. Therefore as the nutritional needs of the different traits are similar, the balance of P:C in the diet of this beetle is unlikely to lead to trade-offs. Nonetheless, nutrition will have lasting effects on male fitness as larvae that develop on optimal diets developed fastest and were larger adults with larger weapons and small genitalia, which confers an advantage in male-male competition, access to mates and insemination success.

    Image caption: Male Gnatocerus cornutus fight using an enlarged mandible which is a secondary sexual trait. Photo credit: Matthew Silk.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Why baby birds differ in the speed at which they grow?

    Riccardo Ton and Thomas E. MartinSometimes bird nests are not easily reachable, and creative thinking is required to access their contents. Photo provided by authors.

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    Baby songbirds grow at very different speeds. In particular, tropical species tend to grow more slowly than similar species in temperate regions. Understanding why is important because speed of growth can have important consequences for the future and survival of the offspring. Growing slowly can be good and give baby birds time to better develop important organs like the brain, muscles and feathers. However slow growth also increases the probability that a predator like a snake or a hawk will find and eat the babies. Conversely, growing quickly helps a baby bird leave the nest early and avoid predators but with organs of lower quality. Despite these implications for survival, it is still unclear why baby birds differ in the speed at which they grow.

    Generally babies of bigger species grow more slowly than those of smaller species. However, songbirds tend not to follow this natural rule. A possible explanation is that metabolism, the set of biochemical reactions that occur in each cell of a living organism, may be the engine propelling growth, but available data on this topic are contradictory. The oxygen that organisms breathe fuels this engine; therefore, if metabolism is the mechanism promoting growth, species that consume more oxygen should grow faster.

    To test the hypothesis that metabolic rate may regulate differences in growth, we measured the oxygen consumed by baby birds sleeping on a nest inside a dark chamber for 59 species in three different continents. We sampled fast growing species in Arizona, USA, slow growing species in tropical Malaysia, and species that grow at intermediate speed in South Africa.

    We found that, for a given body size, growing baby birds from Arizona consumed substantially more oxygen (had higher metabolism) than species from Malaysia or South Africa. We also found that babies of species consuming more oxygen grew faster compared to those species with lower metabolism. Finally, we observed that when differences in metabolism among species were accounted for, baby songbirds do follow the natural pattern that bigger species grow more slowly. However the reasons why metabolism differs among species and latitudes remain unclear and should be the focus of further studies.

    Image caption: Sometimes bird nests are not easily reachable, and creative thinking is required to access their contents. Photo provided by authors.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Effects of neonatal size on maturity and escape performance in the Trinidadian guppy

    Terry Dial, David Reznick and Elizabeth BrainerdImage provided by authors.

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    Newborn offspring are always smaller than the parent, but not all offspring are born the same size or same level of maturity, so what factors ultimately control the evolution of offspring size? Parents balance the tradeoff between offspring size and offspring number, and the optimal balance depends largely on the environment.

    In response to high predation pressure by large predatory fish, Trinidadian guppies produce lots of small babies, flooding their environment with numbers. Above waterfall barriers, in environments with low or no predation, guppies produce fewer, larger babies.

    To avoid a predator, fish will initiate an escape start by first bending their body into a C-shape and then undulating out of it, away from the threat. In other fish studied, larger individuals are known to produce higher performance escape starts. Thus, it is somewhat paradoxical that an adaptation to living with predators is to produce babies that are born with an inherent size disadvantage, but are they?

    Here we measure escape performance of newborn guppies from five populations adapted either to low predation, high predation, or extreme high predation environments. We also measured detailed morphology, both external and internal, to assess whether these offspring possess different body proportions or levels of maturity. We find that those fish responding maximally to our stimulus perform at the upper limit for their size, and that both size and maturity influence this escape performance limit.

    The smallest guppies are extremely slow at performing the escape start, even for their size, and these smallest offspring are also less developmentally mature compared with their larger counterparts. Within the Trinidadian guppy, it appears that both size and maturity tradeoff with number of offspring, and that offspring abundance outweighs performance in environments with the highest predation pressure.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Wood decomposition inside living trees shows that hollows develop slowly but cause a considerable loss of forest biomass

    Zheng Zheng, Shubin Zhang, Carol Baskin, Jerry Baskin, Doug Schaefer and Xiaodong Yang Zhang Shubin is sampling decaying wood from a living tree hollow for measurement of its decay rate by CO2 release, in the Ailao Mountain Forest of China. Picture by Zheng Zheng.

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    Living trees with decayed hollows provide nesting places for animals, especially in old-growth forests throughout the world. These hollows are formed by microorganisms that enter wounds in trunks or large branches and then decompose heartwood. Formation of tree hollows appears to be a slow process because tree hollows usually are found in large trees. However, large hollows formed in some trees indicates that wood decomposition rates there can be high compared to tree growth rates, and that hollow trees store less carbon. While abundance and use by animals of tree hollows have been well studied, the rates at which they form have not been measured.

    In an old-growth subtropical montane forest preserve in southwest China, we measured decomposition rate of wood within tree hollows. From this we estimated the time required to form them. Wood inside tree hollows decomposed about half as fast as decomposing wood on the forest floor. Decomposition was slower because this wood was drier, and had higher density. Tree hollows enlarged by 2 mm per year on each side horizontally and about 8 times faster than that vertically. At that rate it would take 100 years for hollows to become large enough for nests of a local bee species. In addition, decomposition inside hollow trees means stems of living trees in this forest have lost 8·7% of their biomass.

    Image caption: Zhang Shubin is sampling decaying wood from a living tree hollow for measurement of its decay rate by CO2 release, in the Ailao Mountain Forest of China. Picture by Zheng Zheng.
    You can read the article in full here.

     

    Black and yellow plumage signals resistance to oxidative stress in a bird

    Amberleigh E. Henschen, Linda A. Whittingham, and Peter O. Dunn Photo by Matt Tillett. Flickr: via Wikimedia Commons. CC BY 2.0.

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    Choosing a healthy mate is a vital part of female reproductive success as healthier mates may provide benefits to females, such as a better territory or ‘good genes’ that will be inherited by offspring. Male ornaments can help females choose wisely as these often elaborate traits may honestly advertise male health. In particular, it has been suggested that healthier males will have more effective immune systems and efficient metabolism, which will lead to the production of fewer free radicals (e.g., Oxygen ions and hydrogen peroxide). An excess of free radicals leads to an imbalance in cells called oxidative stress, which can damage cells and lead to poorer quality ornaments. Therefore, it is hypothesized that elaborate male ornaments honestly signal the ability of a male to produce immune responses that do not result in oxidative stress. We tested this hypothesis in the common yellowthroat, a warbler in which males have two ornaments, a black face mask and a yellow bib. These ornaments have been studied in both Wisconsin (WI) and New York (NY) and where females choose mates based on the size of the black mask and the size and color of the yellow bib, respectively. As the yellow bib is an honest indicator of oxidative stress in NY, our aim was to determine if the black mask signals similar information in WI. We assessed oxidative stress in males by measuring how resistant red blood cells from each male were to free radicals as well as oxidative stress in the plasma, or non-cellular portion of the blood. As predicted, we found that males with larger masks had red blood cells with greater resistance to oxidative stress. Furthermore, males with larger and more colorful bibs had lower levels of free radicals in the plasma. These results are consistent with the hypothesis that male ornaments indicate the ability of males to manage oxidative stress, but perhaps not in all components of the blood. Photo caption: Male common yellowthroats have two plumage ornaments, a black mask and yellow bib, which are used by females to choose mates. In this study, the authors found that each ornament was related to different measures of the ability to manage oxidative stress.

    Image caption: Photo by Matt Tillett. Flickr: via Wikimedia Commons. CC BY 2.0.
    You can read the article in full here.

     

    Individual-level trait diversity indices

    Simone Fontana, Owen L. Petchey and Francesco Pomati© Studio Asparagus.

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    As humans, we are increasingly concerned about the potential effects of our activities on the structure and functioning of ecosystems. The challenge is to understand if ecosystems will be able to maintain processes and essential functions in a future of lasting human impact (e.g. climate change, pollution). The effects of human-induced environmental change on ecosystem processes might be direct or mediated by changes in the living organisms.

    For this reason, researchers are increasingly considering traits (measurable features of individual organisms, e.g. morphological and physiological characteristics) as a powerful way to explain processes in ecological systems. However, traits are generally assumed not to vary at the species level, thus disregarding the importance of differences between individuals belonging to the same species.

    Our approach considers both differences among individuals and multiple traits at the same time: each individual is placed within a space defined by every measured trait (axes). Thus a species occupies a ‘cloud’ in trait space, and there are basically three different ways to quantify this cloud; trait richness (= trait space occupied by individuals in a community), trait evenness (= regularity in the distribution of individuals within the trait space) and trait divergence (= how spread-out are individuals within the trait space). These characteristics can in turn be measured by various indices, and we can define how we expect each index to change (increase/decrease) if individual organisms are deleted or moved within the trait space. We tested different indices using simulated and real phytoplankton data, to find those with the most appropriate behaviour (that is, the ones changing as expected as a result of our manipulations). The resulting validated set of indices includes FDis (trait divergence) and two newly proposed metrics: TOP (= Trait Onion Peeling; trait richness) and TED (= Trait Even Distribution, trait evenness).

    These three components of trait diversity, used in a complementary approach, may shed light on the importance of differences among individuals in natural ecosystem processes and improve our understanding of the pathways by which environmental changes affect ecosystem functioning through biodiversity change.

    Image caption: © Studio Asparagus.
    You can read the article in full here.

     

    Water use by Swedish boreal forests in a changing climate

    Thomas B. Hasper, Göran Wallin, Shubhangi Lamba, Marianne Hall, Fernando Jaramillo, Hjalmar Laudon, Sune Linder, Jane L. Medhurst, Mats Räntfors, Bjarni D. Sigurdsson, Johan UddlingSwedish boreal landscape (left; © Thomas B. Hasper) and Flakaliden Whole-Tree Chamber Experiment (right; © Bengt-Olof Vigren).

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    The ongoing increases in atmospheric carbon dioxide concentration ([CO2]) and temperature have the potential to alter the flux of water vapor through plant leaf ‘stomata’, tiny and actively regulated pores in the leaf surface. This flux, transpiration, in turn regulates the terrestrial water and energy balance and, thus, influences local and regional hydrology and climate.

    Combined stomatal-photosynthesis models employed in ecosystem and climate models predict decreases in stomatal conductance and land evapotranspiration (ET) at elevated [CO2]. This stomatal water-saving response to increased [CO2] has been used to explain the observed increase in global river runoff during the past century. Plant water use is, however, also affected by changes in air temperature, precipitation and land-use, and there is yet no consensus about the contribution of different drivers to temporal trends of ET and river runoff.

    In this study, we examined the water-use responses of Swedish boreal forests to climate change by using long-term monitoring as well as experimental data. We used climate and runoff data of large-scale boreal landscapes from the past 50 years to explore historical trends and patterns in ET. In addition, we examined explicit tree water-use responses to elevated [CO2] and/or air temperature in a whole-tree chamber experiment using mature Norway spruce trees.

    The results demonstrated that ET increased by 18% over the past half century while river runoff did not significantly change. The increase in ET was related to increasing precipitation and a steady increase in forest standing biomass over this period. The whole-tree experiment showed that Norway spruce trees did not use less water under elevated [CO2] and that elevated air temperature did not increase plant transpiration as decreased stomatal conductance neutralized the effect of higher evaporative demand in warmed air.

    Our findings have important implications for projections of the future hydrology of European boreal coniferous forests, indicating that changes in precipitation and standing biomass are more important than effects of elevated [CO2] or temperature on tree transpiration rates.

    Image caption: Swedish boreal landscape (left; © Thomas B. Hasper) and Flakaliden Whole-Tree Chamber Experiment (right; © Bengt-Olof Vigren).
    You can read the article in full here.

     

    Nitrogen deposition affects Scots pine stoichiometry

    Jordi Sardans, Rocio Alonso, Ivan Janssens, Jofre Carnicer, Stavros Vereseglou, Mathias Rillig, Marcos Fernández-Martínez, Tanja Sanders and Josep Peñuelas Pinus sylvestris forests at the Southern limit of its distribution area, such as in this photo in a Pyrenees valley, are subject to several stresses, from drought to excess light, that threaten their survival. The impacts of these stresses on plant-soil nutrient cycles and nutrient ratios can be crucial for the future of this species in several parts of Europe. Credit Dr. Oriol Grau.

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    The spatial and temporal patterns of nitrogen (N) and phosphorus (P) concentrations and of N:P ratios in terrestrial plant communities have been shown to be related to several ecosystem processes. Little is known, however, about the flexibility of N and P concentrations or of N:P ratios in terrestrial plant species along their natural ranges of distribution in response to natural and anthropogenic gradients, or of their ecological significance. Pinus sylvestris (Scots pine) is one of the most important forest species in Eurasia, with a broad distribution extending from Spain to Siberia. This broad distribution across Europe offers a unique opportunity to study the relationships between soil and plant nutrient concentrations, and how these vary with climate, atmospheric N deposition and plant growth. In this study, we investigated needle N and P concentrations, N:P ratios and soil elemental composition and their shifts in response to climatic gradients and atmospheric N deposition in P. sylvestris forests. We also investigated the relationship of these variables with P. sylvestris growth by analyzing a compiled dataset of 2245 stands of P. sylvestris throughout Europe. The results showed that N deposition was positively correlated with needle N concentration and N:P ratio and negatively with needle P concentrations. This was especially pronounced at sites where high levels of N deposition coincided with higher mean annual temperature and higher mean annual precipitation, such as in central Europe. Atmospheric N deposition was also negatively correlated with soil plant-available P and K concentrations. Higher soil-solution nitrate:P ratios coincided with higher needle N:P ratios at higher levels of N deposition. The relationships between needle and soil-solution nutrient concentrations indicated that other elements, such as potassium, could also be involved in soil nutritional disequilibrium. Despite these nutrient imbalances, N deposition was positively related to Pinus sylvestris absolute basal diameter growth.

    These results thus indicate a tendency of European P. sylvestris forests to store N in trees and soil in response to N deposition, and strongly suggest a trend toward increased nutrient losses in runoff related to higher soil-solution N concentrations.

    Image caption: Pinus sylvestris forests at the Southern limit of its distribution area, such as in this photo in a Pyrenees valley, are subject to several stresses, from drought to excess light, that threaten their survival. The impacts of these stresses on plant-soil nutrient cycles and nutrient ratios can be crucial for the future of this species in several parts of Europe. Credit Dr. Oriol Grau.
    You can read the article in full here.

    Special Feature: The functional role of silicon in plant biology

    The Importance of Agriculture in Global Biogenic Silicon Production

    Joanna C. Carey and Robinson W. FulweilerCorn farm in central Pennsylvania. Photo: fishhawk via Flickr (CC BY).

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    Our human footprint on the Earth is so large that many scientists assert we have ushered in a new geological epoch – the Anthropocene. Human impacts on the Earth are well-documented. We have cut down forests, dammed rivers, overfished the seas, and added enough extra carbon dioxide to our atmosphere to increase global temperatures. We have also fundamentally changed how we grow our food. Industrialized agriculture has altered a range of ecosystem processes, perhaps the most fundamental of which is nutrient cycling. While the impacts of agriculture on the nitrogen and phosphorus cycles are well-described, we know much less about how agriculture has changed the global silicon (Si) cycle.

    We care about Si for many reasons. Weathering of silicate rocks plays a key role in regulating atmospheric carbon dioxide concentrations over long time periods. Additionally, Si is an essential nutrient for diatoms, small photosynthetic plankton (think ‘grasses of the sea’) that consume carbon dioxide. Diatoms also support economically, nutritionally, and culturally important marine food webs. Si also turns out to be a ‘quasi-essential’ nutrient for land plants, as it protects them from stressors such as drought, herbivory, and heavy metal toxicity.

    Land plants take up dissolved silica and it becomes deposited within their tissues as biogenic Si. Agricultural crops account for approximately 35% of the biogenic silica fixed globally by land plants, not only because of their large biomass, but also because they tend to have high Si concentrations in their tissues. In the last fifty years (1961-2012) biogenic silica production in the ten most productive agricultural crops has more than tripled, and we predict that by 2050 biogenic silica production may increase by another 50%.

    Compared to mineral silicates, biogenic silica is considered ‘bio-available’ and is rapidly regenerated and available for subsequent uptake by terrestrial or aquatic organisms. In turn, the substantial increase in biogenic silica production is augmenting the reservoir of biologically available Si on Earth. As a result, the fate of the biogenic silica removed from agricultural areas via plant harvest is important, with implications for global carbon cycling and marine food webs.

    Image caption: Corn farm in central Pennsylvania. Photo: fishhawk via Flickr (CC BY).
    You can read the article in full here.

     

    Unseen consequences of losing large wildlife: increases in rodent immune function following large mammal defaunation

    Hillary S. Young, Rodolfo Dirzo, Kristofer M. Helgen, Douglas J. McCauley, Charles L Nunn, Paul Snyder, Kari E. Veblen, Serena Zhao and Vanessa O. EzenwaZebras. Photo provided by authors.

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    Ecosystems around the world are losing large wildlife due to overexploitation, development of agriculture, and increased human densities. While research has examined the consequences of losing large-bodied animals for the abundance and composition of the smaller animals that remain, little research has considered how these changes affect animal physiology. This is a critical oversight because changes in animal physiology can have enormous consequences for ecosystem functioning and processes, including spread of disease.

    We examined the effect of large wildlife removal on immune function in rodents using a large-scale exclosure experiment in Kenya, where high voltage electrified fences have effectively remove all large wildlife from plots for the past 20 years. Examining a suite of immune parameters in the most common mouse species in these plots, we found evidence of significant increases in immune function of rodents when large wildlife are absent. This effect may result from a higher number of parasites in defaunated ecosystems, which drives an increase in need for immune protection. Alternatively, observed changes may result from increased food availability in the landscape when large herbivores are removed, which allows for more energy to be devoted to immune functions. Either way, our research indicates that loss of large wildlife could have major consequences for rodent-borne disease dynamics via changes in immune function. For example, such changes may reduce the likelihood that increased parasite density in landscapes without large wildlife may translate to realized increases in disease prevalence in rodents.

    Image caption: Zebras. Photo provided by authors.
    You can read the article in full here.

    Special Feature: Mechanisms and consequences of facilitation in plant communities

    Facilitation among plants as an insurance policy for diversity in Alpine communities

    Lohengrin A. Cavieres, Carolina Hernández-Fuentes, Angela Sierra-Almeida and Zaal Kikvidze  Laretia acaulis cushion harbouring native grasses in the high alpine of central Chile Andes.

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    Positive interactions among plant species occur when the presence of one plant species enhances the chances that another species co-occurs in the same place, indicating that positive interactions may determine biological diversity. Although early research focused on (negative) interactions such as competition and predation as the main factors structuring plant communities and regulating biological diversity, positive interactions have started to gain a place in the ecological literature. However their role in determining diversity at different spatial scales has been poorly explored.

    Nurse plants are those that provide shelter to other plant species from environmental severity (e.g. strong winds, extreme low temperature, etc.) or herbivory, and are one of the most commonly recognized examples of positive interactions among plants. It has been suggested that the presence and importance of nurse plants are higher in environmentally severe environments such as alpine or desert habitats, where the mitigation of extreme conditions by the nurse species can be beneficial to many other species.

    The majority of the studies addressing the consequences of nurse plants for diversity have compared the diversity of plant assemblages growing within nurses vs. those growing outside them, reporting contrasting results among them. Nonetheless, nurses and their alternative microhabitats (open areas between nurses) are part of the same community. Thus, if nurses allow for the persistence of species that otherwise would be excluded, a net increase in species diversity of the whole community will be generated even if areas under nurse plants contain fewer species than the open areas outside them.

    In this study we conducted a bibliographic search using the ISI-Web of Knowledge database and reviewed the literature on alpine plant communities where assessments of the diversity of plants growing within and outside nurse species were available. We found that in most cases, nurse species substantially increased species richness, despite the fact that in some cases they contained lower species numbers than surrounding open areas. Strikingly, nurse species enhanced species richness more in sites with more severe environmental conditions, suggesting that facilitative interactions in alpine habitats act as an insurance policy that sustains diversity under very harsh environmental conditions.

    Image caption: Laretia acaulis cushion harbouring native grasses in the high alpine of central Chile Andes.
    You can read the article in full here.

     

    Flowers avoiding bees? The case of Costus arabicus colour variation sheds light on bee sensorial exclusion hypothesis for hummingbird red-flowers

    Pedro Joaquim Bergamo, André Rodrigo Rech, Vinícius L. G. Brito and Marlies SazimaPink flowers of Costus arabicus, presumably avoiding bee-pollination.  Photo credit: Camila Silva Oliveira.

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    Floral colour plays a role in plant-pollinator communication by signalling floral resources. Hummingbirds are often associated with red coloured flowers, and there are two tentative hypotheses to explain this association: 1. hummingbirds are attracted to red due its easier detection and, 2. bees are sensorialy excluded from red flowers. The second hypothesis is based on bees' red colour blindness, which leads them to be less frequent and less important than hummingbirds as pollinators of red-reflecting flowers. In this sense, red-reflecting flowers could adopt a "bee avoidance" strategy. Here we empirically tested the above hypotheses. We chose Costus arabicus, which has white- and pink-flowered individuals and is pollinated by both bees and hummingbirds. Specifically, we tested whether differences in red reflectance attracts hummingbirds (expecting more hummingbird visitation of pink flowers) or excludes bees (and then, expecting bee avoidance of pink flowers) and the consequent implications for the plant’s reproduction. Flower colour morphs of C. arabicus differed only in petal red-reflectance. Using vision models, the white flowers were revealed to be easily detected by bees and the pink flowers by hummingbirds. Bees preferentially visited the white flowers, whereas hummingbirds visited both colours at the same rate - both patterns corroborating the bee avoidance hypothesis. Pollen loads deposited on flowers stigmas did not differ between flower colour morphs, indicating that bees and hummingbirds play a similar role in the quantity aspect of pollination. However, bees are more likely to self-pollinate C. arabicus flowers than hummingbirds. We also found that self-pollination limits C. arabicus reproduction, and red-reflecting flowers may enhance the quality aspect of pollination by discouraging bee visitation. Sensory exclusion of bees seems to be the pressure for evolution of red-reflecting flowers, driving specialisation in hummingbird-pollinated flowers due to the costs of bee pollination on plant reproduction.

    Image caption: Pink flowers of Costus arabicus, presumably avoiding bee-pollination. Photo credit: Camila Silva Oliveira.
    You can read the article in full here.

     

    Multiple environmental drivers structure plant traits at the community level in a pyrogenic ecosystem

    Gregory M. Ames, Steven M. Anderson and Justin P. WrightA longleaf pine savanna experiencing a prescribed burn, Fort Bragg, NC. Photo by Gregory Ames, 2012.

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    Biodiversity is declining at unprecedented rates and this decline may negatively impact ecosystem functions that we depend on. Preserving functional diversity requires an understanding of how it responds to changes in environmental conditions. Measureable properties of plants that affect performance, i.e. functional traits, provide a measure of functional diversity that is independent of species identity and can be compared across systems containing different species. However, little is known about the relationship between functional traits and environmental forcing, or how local trait variability influences our understanding of this relationship.

    We measured traits that are strongly associated with growth and survival strategies of plants in the understory communities of longleaf pine forests that experience periodic fire, to investigate how this strong disturbance interacts with environmental conditions to drive changes in functional traits. We also investigated which environmental factors are most associated with changes in community composition without considering functional traits.

    We found that a small set of environmental factors explained a large amount of the variation in key traits, but that the factors explaining community composition and functional traits were different. In particular, we found that functional traits were primarily explained by interactions between environmental factors such as fire, precipitation, and soil texture. This shows that strong environmental gradients cannot be considered independently of one another.

    Furthermore, our interpretations of which environmental factors were most important depended on whether or not we used functional trait values from across the landscape or just the local plot-level measurements. This shows that it is essential to account for local variability in species traits when trying to infer relationships with the environment, especially in landscapes with strong disturbance gradients like those imposed by fire.

    Our results are important because they show that understanding the response of functional diversity to the environment requires consideration of multiple environmental factors as well as their interactions, as well as the use of locally measured trait values. Incorporating these elements into future trait-based studies will greatly improve our understanding of how functional diversity responds to environmental changes.

    Image caption: A longleaf pine savanna experiencing a prescribed burn, Fort Bragg, NC. Photo by Gregory Ames, 2012.
    You can read the article in full here.

     

    Frog habitat preferences do not maximize jumping performance

    Allegra Mitchell and Philip J. Bergmann Photo credit: Philip J Bergmann.

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    Predicting species responses to a changing climate is difficult because of the dynamic relationship between animals and their environment, but it is necessary to reduce species losses. Amphibians in particular are suffering population declines globally, and understanding how the environment influences their habitat preferences and physical performance is crucial to understanding how these animals will be influenced by climate change. The biology of amphibians makes them especially sensitive to changes in environmental temperature and moisture because they are cold blooded and have highly water-permeable skin. Therefore, changes in environmental temperature and moisture directly affect amphibian body temperature and hydration level. Amphibians should select habitats with the optimal combination of temperature and moisture to perform tasks necessary for survival, like escaping predators or capturing prey. However, interactions between environmental temperature and moisture can influence habitat selection and task performance in different and often unpredictable ways.

    In our study, we tested how environmental temperature and moisture influenced temperature and moisture preferences, and jumping performance in Green Frogs (Lithobates clamitans) in the laboratory and the field. We found that frogs in the laboratory selected environmental conditions that minimized water loss through the skin, rather than maximized body temperature to allow them to jump better. Frogs in the field also preferred to be well hydrated, and allowed their body temperatures to be much more variable. Jumping performance was highest at higher temperatures, but higher temperatures also increase dehydration. Therefore, conditions that minimized water loss frequently did not maximize jumping performance, creating a discrepancy between remaining hydrated and moving effectively.

    The ecology of Green Frogs may explain this discrepancy because the frogs remain near bodies of water that serve as refuges from both dehydration and many predators. However, when it is warmer and drier, Green Frogs may be more likely to select microhabitats that minimize the risk of dehydration at the expense of their ability to forage and escape from predators. As the climate changes, all amphibians may be at greater risk of dehydration and predation, particularly those that are already declining.

    Image caption: Photo credit: Philip J Bergmann.
    You can read the article in full here.

     

    Tracking woodland water use efficiency under future atmospheric conditions

    Teresa E. Gimeno, Kristine Y. Crous, Julia Cooke, Anthony P. O’Grady, Anna Ósvaldsson, Belinda E. Medlyn and David S. Ellsworth A view of the EucFACE study site from the top of a crane inside one of the study rings taken while making a gas-exchange measurement campaigns by Teresa E. Gimeno.

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    The most certain prediction for our atmosphere is that carbon dioxide (CO2) concentration will continue to rise, due to fossil fuel burning. Rising CO2 affects the biosphere indirectly because it is the main driver of climate change, but it also has a large direct impact on vegetation because it is the main fuel for plant growth. However, when plants take up CO2, it is accompanied by an inevitable loss of water. This process of transpiration is regulated by the opening and closing of small pores (called stomata) found on the leaf surface of all higher plants. In an atmosphere with more CO2, plants can close stomatal pores to economize on water, while maintaining or even increasing CO2 uptake. This means that plants can increase how efficiently they use water with rising CO2. This increase is particularly relevant for ecosystems where plant growth is limited by water availability, including the vast majority of Australian forests and woodlands.

    Previous experiments showed that rising CO2 could increase or decrease water use efficiency depending on plant types and climates. Fortunately, models help to predict optimal water use per unit of CO2 uptake, based on the sensitivity of stomatal pores to the environment. Here we tested the ability of one of these models to predict water use efficiency during carbon uptake in future atmospheric conditions, under variable climatic conditions. To test for optimal stomatal behaviour of the trees, we measured carbon uptake and water use at the tops of mature eucalypt trees under current and future CO2 atmospheric concentrations, over the course of the seasons. Our study was conducted at the EucFACE site, the only existing elevated CO2 experiment in a native Eucalyptus forest. We show that water use efficiency increases proportionally with the rise in CO2 concentration. So in a future global change scenario, mature trees will be more efficient in their water use, but this may only partially mitigate some of the adverse effects of the concomitant rise in temperature.

    Image caption: A view of the EucFACE study site from the top of a crane inside one of the study rings taken while making a gas-exchange measurement campaigns by Teresa E. Gimeno.
    You can read the article in full here.

     

    Breath of death: how a parasite favours its transmission through hijacking its host’s hypoxia-acclimation processes

    Marie-Jeanne Perrot-Minnot, Matthieu Maddaleno, Frank Cezilly The thorny-headed worm Polymorphus minutus : larvae dissected from the crustacean host, and infective to the definitive host, a waterbird.

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    Parasites with complex life cycles, involving more than one host, often alter the behaviour of their intermediate hosts in ways that increase their chances of getting transmitted to final hosts. For instance, the thorny-headed worm Polymorphus minutus is known to induce ‘reversed geotaxis’ in its amphipod host Gammarus roeseli, such that infected hosts swim closer to the water surface and presumably become more vulnerable to predation by aquatic birds (in which the parasite will complete its life cycle).

    So far, the mechanisms underlying host manipulation by parasites remain poorly known. As hypoxia (shortage of oxygen) in aquatic invertebrates is known to induce complex physiological responses and reversed geotaxis, we conjectured that the reversal of geotaxis induced by P. minutus in amphipod hosts could result from a hypoxia-like state through two potential mechanisms. First a decrease in the metabolic rate of amphipods could be directly caused by infection with P. minutus. Second, the parasite could mimic a state of hypoxia in its host, as P. minutus has been previously shown to excrete both lactate and succinate (two end-products of its own anaerobic metabolism).

    Under hypoxia, uninfected G. roeseli showed negative geotaxis and lower metabolic rate, two traits altered by infection with P. minutus, albeit with different intensities. The injection of a mixture of lactate and succinate in uninfected amphipods also mimicked the parasite-induced reversion of geotaxis, without affecting metabolic rate. In addition, both P. minutus-infected gammarids and uninfected ones conditioned to hypoxia for two days showed elevated levels of lactate in the brain, but not in the haemolymph (the fluid analogous to blood in vertebrates). Overall, our results strongly suggest that the pathways involved in anaerobic metabolism and hypoxia-signalling might be responsible for the changes in geotaxis and metabolic rate induced by P. minutus infection.

    This study emphasizes the need to consider the tight and complex connections between physiological processes and behavioural adjustments, in particular at the brain level, in the understanding of parasitic manipulation, and more broadly of behavioural changes in infected hosts.

    Image caption: The thorny-headed worm Polymorphus minutus : larvae dissected from the crustacean host, and infective to the definitive host, a waterbird.
    You can read the article in full here.

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