Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

  • Why do lizard dewlaps glow? Fleishman et al
  • Plants helping plants for sustainable agriculture Brooker et al
  • How should the number of leaves along branches in a plant canopy change with leaf size? Huang et al
  • The effects of background risk on behavioural lateralization in a coral reef fish Ferrari et al
  • Leaf traits of vascular epiphytes shift with height above the forest floor Petter et al
  • Plants respond to herbivory by producing more prickles, thorns, and spines Barton
  • Evolution of nutrient acquisition: when space matters Barot et al
  • Defenders in the Tundra: Plant defense is determined by nutrient availability and elevation De Long et al
  • Parent-offspring co-adaptation in a wild bird Lucass et al
  • The relationship between microhabitat use, allometry, and functional variation in the eyes of Hawaiian Megalagrion damselflies Scales & Butler
  • Glucocorticoid manipulations in free-living animals: considerations of dose delivery, life-history context, and reproductive state Crossin et al
  • Evidence of trophic specialization in cave species challenges the usual prediction of generalist feeding in food-limited environments Francois et al
  • Seed transport by physically active animals: farther than we think? van Leeuwen et al
  • What can we predict about a forest based on the sizes of its trees? Anderson-Teixeira et al
  • Big, warm woodlice “chill out”, rather than cross a habitat corridor Barnes et al
  • Nitrogen saturation in humid tropical forests after 6 years of nitrogen and phosphorus addition: hypothesis testing Chen et al
  • Arboreality and associated gravitational stress on blood circulation have influenced the evolution of tail length in snakes Sheehy et al
  • How is wood decomposition affected by nutrients in a tropical forest? Chen et al
  • Xylem vessel traits tell the timing of leaf emergence and senescence in native and non-native understory species of temperate deciduous forests Yin et al
  • Agriculture increases temporal variability of stream ecosystem functioning Tolkkinen et al
  • Plasticity in sexual size dimorphism Bonneaud et al
  • Subordinate plants and fungi: what happens when these minorities join the effort? Mariotte et al
  • Birth date predicts alternative life history pathways in a fish with sequential reproductive tactics Fagundes et al
  • An invasive plant evolves rapidly in response to changes in climate Colomer-Ventura et al
  • Wood mice select foraging site according to the extent of within-plant variability in seed characteristics Shimada et al
  • A portfolio effect of shrub canopy height on species richness along a competitive stress gradient Bråthen and Lortie
  • Stress, immunity, and energy use in snakes Neuman-Lee et al
  • Preferred nest-sites help female song sparrows successfully raise chicks in early spring conditions Germain et al
  • Moving Beyond Body Condition Indices as an Estimate of Fitness in Ecological and Evolutionary Studies Wilder et al
  • Jack of all foods or master of one: symbiotic bacteria determine the diet of an insect pest Wagner et al
  • Does history matter in plant interactions? Wurst & Ohgushi
  • The double-edged sword of immune defence and damage control: Do food availability and immune challenge alter the balance? Stahlschmidt et al
  • Darwin’s dream: a manipulative experiment for measuring natural selection in animal populations Bartheld et al
  • Neighbour presence reduces root allocation Chen et al
  • Burn or rot: leaf traits explain why flammability and decomposability are decoupled across species. Grootemaat et al
  • Food availability and seasonal reproductive activation in a songbird Davies et al
  • Does size really matter in predicting bite force in bats? Senawi et al
  • Cane toad impacts native species reproduction Narayan et al
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    Why do lizard dewlaps glow?

    Leo J. Fleishman, Brianna Ogas, David Steinberg and Manuel LealA glowing dewlap. Photo Credit: Manuel Leal. The lizard Anolis lineatopus inhabits shaded forests throughout the island of Jamaica.  Territorial males extend a colorful throat fan – the dewlap – in visual displays that attract females and repel male rivals. The dewlap is translucent: it transmits and diffuses light striking its back surface.  In this picture the sun is located behind the animal, and the sunlight transmitted through the dewlap makes it appear to glow.  The translucent properties of the dewlap make its colors more vivid and easier to see.

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    Many animals use impressive color patterns to communicate with other members of their species. Since most animals do not produce light themselves, these colored surfaces are only visible because they reflect natural light. In bright sunlight, reflected colors often appear intense and brilliant. In heavily shaded habitats, where most of the sunlight is blocked, the same colors often appear much duller, and different colors can be difficult to tell apart.

    Anolis lizards are well known for their use of a colorful, expandable throat fan, called the dewlap, to attract mates and repel rivals. There are hundreds of species of anoles. They are active only during the day, but many species live in heavily shaded forest habitats where colors can be difficult to see. The dewlap is a very thin structure, and for this reason, some of the light that strikes its surface transmits through it, becoming colored and spreading in all directions as it does. If strongly lit from behind – for example when the sun is on the opposite side of the dewlap from the viewer – the dewlap appears to glow brilliantly, because the light passing through it is made colored and diffuse by the pigments in the dewlap. A color pattern of this type is referred to as translucent.

    We explored the reasons why some species of anoles have evolved translucent dewlaps. Those with the most translucent dewlaps live in shaded forest habitats, where light levels are relatively low. When an anole opens its dewlap much of the light striking the back surface (opposite the viewer) passes through the dewlap. This adds to the light reflected back from the front surface (facing the viewer) and greatly increases the total light intensity reaching the viewer’s eyes. This makes the dewlap color much easier to detect, and to distinguish from other colored objects in the habitat. Mates and rivals can, therefore, quickly detect and identify the species of the displaying animal. This is the first study to demonstrate the evolutionary advantage of possessing a translucent display organ that utilizes diffuse transmitted light to increase its visibility.

    Image caption: A glowing dewlap. Photo Credit: Manuel Leal. The lizard Anolis lineatopus inhabits shaded forests throughout the island of Jamaica. Territorial males extend a colorful throat fan – the dewlap – in visual displays that attract females and repel male rivals. The dewlap is translucent: it transmits and diffuses light striking its back surface. In this picture the sun is located behind the animal, and the sunlight transmitted through the dewlap makes it appear to glow. The translucent properties of the dewlap make its colors more vivid and easier to see.
    You can read the article in full here or watch a video on this reserach below:

    Mechanisms and consequences of facilitation in plant communities

    Plants helping plants for sustainable agriculture

    Rob W. Brooker, Alison J. Karley, Adrian C. Newton, Robin J. Pakeman and Christian Schöb Harvesting a study of the impact of barley mixtures on rare and common weed species.

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    Plant competition is the negative interactions that occur when two plants try to use the same pool of resources such as nutrients, particularly when that pool is only of limited size. The opposite of plant competition is plant facilitation, which occurs when one plant has a beneficial effect on its neighbour, for example by providing it with some kind of nutrient that it would otherwise lack, or sheltering it from extreme environmental conditions or the attentions of herbivores. Recently there has been a remarkable increase in our understanding of plant facilitation, particularly in more severe environments such as arctic, alpine or desert ecosystems.

    However, in this paper we describe how facilitation could play an important role in making agricultural systems – particularly crop systems – more sustainable. We look at three main groups of beneficial interactions. First we briefly discuss the beneficial interactions that occur between different crop species in intercropping systems. Second we consider beneficial interactions between different varieties (genotypes) of the same crop species – these underpin what are known as crop mixture effects. In both cases many of the benefits come from maintaining crop yields whilst reducing the use of agricultural chemicals. Third we describe new research which suggests that some rare plant species may depend directly on crops for their survival.

    We end by considering how we can link our ecological understanding of facilitation in crop systems to new management practices that might benefit biodiversity. In some cases no work is needed: intercropping and variety mixtures are already widely used, and the challenge is to encourage greater uptake of these approaches. In the case of conserving rare plants that depend on the crop, we are much further away from converting new knowledge into management practices for nature conservation. Overall, however, it is clear from the evidence we provide that facilitative plant interactions can play a central role in making crop systems more sustainable.

    Image caption: Harvesting a study of the impact of barley mixtures on rare and common weed species.
    You can read the article in full here.

     

    How should the number of leaves along branches in a plant canopy change with leaf size?

    Yingxin Huang, Martin J. Lechowicz, Charles A. Price, Lei Li, Ying Wang and Daowei ZhouSongnen Grassland. Photo provided by authors.

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    The three dimensional array of leaves and branches that comprise a plant canopy functions primarily as an integrated system for the capture of solar energy and the uptake of carbon dioxide in photosynthesis. The placement of leaves along branches, influenced by both leaf size and number, affects the whole plant architecture and resource economics in numerous ways. If a species has large leaves, they must be spaced farther apart to avoid self-shading. Conversely, a species with small leaves can pack more leaves onto a branch before self-shading is an issue. Given two species differing in the size of their leaves, can we predict how many leaves they will have relative to the amount of branch – their leafing intensity?

    Working from established principles, we show algebraically that the relationship between leaf size and leafing intensity depends on the density of branch tissues. The allocation of biomass to leaves versus branches interacts with the density of branch tissue to determine the size and number of leaves on branches within a given volume of a plant canopy. When the relative biomass investments in leaves vs branch tissues as well as the density of branch tissues are constant, then leafing intensity will differ in simple inverse proportion to leaf size. That is, a species with leaves 10% bigger than another species will have a 10% smaller leafing intensity. Conversely, any change in the density of branch tissue will affect the relationship between leaf size and leafing intensity. Leafing intensity will still be smaller in the species with bigger leaves, but the leafing intensity will not diminish proportionately to changes in leaf size. We affirmed these predictions in comparisons of wildflowers growing in the Songnen Grasslands of northwestern China. These results emphasize the importance of considering the complex tradeoffs among traits that influence adaptive evolution of the structure of plant canopies.

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

     

    The effects of background risk on behavioural lateralization in a coral reef fish

    Maud C.O. Ferrari, Mark I. McCormick, Bridie J. M. Allan, Rebecca B. Choi, Ryan Ramasamy and Douglas P. ChiversImage provided by authors.

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    Many animals show an asymmetry (or lateralization) in their organ use, much like human handedness. For instance, some birds use only their left eyes to recognize environmental cues used during migration. Given that numerous studies have reported many benefits associated with this asymmetry, it is somehow surprising to see the variability in the degree of lateralization within and across populations, species and taxa. A few studies have reported changes in the degree of lateralization of individuals, in response to long-term changes in environmental conditions. However, we do not know if short-term changes in conditions could change the degree of lateralization displayed by an individual. Predation is highly variable over both space and time. Thus, predation risk is a potential factor that could induce such changes.

    Here, we exposed wild-caught juvenile damselfish to a high or low background level of risk for four days and showed that the fish subsequently differ in their turning bias. Fish from the low-risk environment did not display a strong turning preference, while fish from a high-risk background showed a strong turning bias (turning more consistently right or consistently left), a trait previously linked to increased chance of escape during predator attacks. Fish from the high-risk background also had higher survival when released into experimental environments containing reef predators. This demonstrates that lateralization, traditionally thought of as a fixed trait, is rather flexible. More work is needed to investigate the mechanism underlying this plasticity.

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

     

    Leaf traits of vascular epiphytes shift with height above the forest floor

    Gunnar Petter, Katrin Wagner, Wolfgang Wanek, Eduardo Javier Sánchez Delgado, Gerhard Zotz, Juliano Sarmento Cabral, Holger KreftResearch crane at the San Lorenzo Canopy Crane Site in Panama (left). Prosthechea sp. (Orchidaceae) in flower; leaves of Serpocaulon wagneri (Polypodiaceae) and Stenospermation angustifolium (Araceae; right, from top to bottom). (Photos by G. Petter).

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    Leaves control the water and carbon balance of plants. Leaf traits can thus strongly influence growth and survival of plants under different environmental conditions. In dry areas, for instance, plants with thick and leathery leaves are often more successful, illustrating a linkage between leaf traits and the environment. Environmental gradients offer great opportunities to study how environmental conditions affect leaf traits, and which traits are functionally important. Within forests, environmental conditions change gradually with height above the forest floor, from the dark and humid understory to the sunnier and drier outer canopy. Vascular epiphytes, which are plants growing non-parasitically on trees, are exposed to all these different conditions, making them particularly useful for studying how such vertical gradients affect the vertical distribution of leaf traits within and across species. A few studies have compared epiphyte traits at different heights or different positions within trees, but none so far has systematically examined changes in leaf traits along the entire height gradient.

    In this study, we analyzed the relationship between several leaf traits of epiphytes and height in a Panamanian lowland rainforest. We accessed the canopy with a research crane. For most traits, the average trait value changed with height, but the pattern of change differed between traits. For instance, while the average leaf thickness increased gradually with height, the average specific leaf area (leaf area/leaf dry mass) decreased strongly only in the first meters above the forest floor. Such trends were similar within the major taxonomic groups of epiphytes (orchids, ferns, bromeliads, aroids), but mean trait values between these groups sometimes differed substantially. Interestingly, trait shifts were also observed within species, indicating that individuals of the same species can respond to environmental changes even over only a few meters of height. We also found that species with higher leaf trait variability occurred at a greater range of heights within the forest. In summary, we observed a link between leaf traits and the vertical environmental gradient within forests at community and species level, contributing to our understanding of the vertical distribution and trait composition of epiphyte communities.

    Image caption: Research crane at the San Lorenzo Canopy Crane Site in Panama (left). Prosthechea sp. (Orchidaceae) in flower; leaves of Serpocaulon wagneri (Polypodiaceae) and Stenospermation angustifolium (Araceae; right, from top to bottom). (Photos by G. Petter).
    You can read the article in full here.

    Review

    Plants respond to herbivory by producing more prickles, thorns, and spines

    Kasey E. Barton Hawaiian prickly poppy. Photo provided by author.

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    Anti-herbivore plant defense is highly variable, changing within plants as they grow, and in response to their environments. Induced defenses occur when plants respond to herbivory by increasing defense traits. While considerable research has examined how plant defensive chemistry changes after herbivory, often leading to more poisonous and better defended plants, relatively little is known about herbivore-induced changes in physical defenses.

    Plant physical defense traits include external structures that deter herbivores such as hairs, spines, thorns, and prickles, as well as internal cellular structures, such as calcium oxalate crystals and lignin, that make leaves tough to digest. Like defensive chemicals, physical defense traits may increase following herbivory, making plants better defended against future attacks. However, because induction of physical defense traits requires the growth of new tissues (with more prickles or tougher leaves), it is slower than chemical induction, leading scientists to predict that physical trait induction is likely to be less common and of lower magnitude than chemical induction.

    In this study, we performed a meta-analysis to examine general patterns in the induction of physical defense traits. All studies that have been published on physical trait induction were identified, and the data for defense traits in undamaged control vs. damaged treatment groups were extracted and analyzed together.

    The results reveal that physical trait induction is common and widespread. In contrast to the prediction, the magnitude of physical trait induction (52%) was not lower than chemical trait induction (43%), and was actually slightly higher. Interestingly, not all physical defense traits are inducible to the same degree. Non-glandular hairs showed the greatest induction (mean 82%), while prickles (40%), spines (26%) and thorns (54%) showed weaker, but still significant increases. Leaf toughness did not respond to damage, perhaps because leaf toughness is more important for eco-physiological functions.

    This research highlights some general patterns in plant induced responses to herbivory. However, it also reveals important gaps in our knowledge. For example, very few studies actually examine whether the induction of more prickles, thorns, and spines actually improve defense against future attacks. Therefore, the ecological and evolutionary significance of these responses remain unclear.

    Image caption: Hawaiian prickly poppy. Photo provided by author.
    You can read the article in full here.

     

    Evolution of nutrient acquisition: when space matters

    Sébastien Barot, Stefan Bornhofen, Simon Boudsocq, Xavier Raynaud and Nicolas Loeuille Grass layer of the savanna in Hwange National Park, Zimbabwe. Photo provided by authors.

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    Ecologists have extensively studied plant strategies (sets of characteristics that allow plants to survive and reproduce in particular environments), and a key characteristic of these strategies is the rate at which plants acquire mineral nutrients from soils. This rate should not only strongly influence the success of plant species confronted by competition for resources, but should also have an impact on ecosystem characteristics such as the availability of mineral nutrients or primary production. Meanwhile, evolutionary ecology has paid little attention to the evolution of traits, such as the rate of nutrient uptake, that affect fitness (measured as the number of descendants) only indirectly but are closely linked to ecosystem functioning. Using a theoretical approach, we therefore studied the evolution of the rate of nutrient uptake and the consequences of this evolution for ecosystem characteristics. We built a spatially-explicit simulation model where a limiting nutrient is recycled in local patches by individual plants. The model includes both local competition for the local nutrient source in each patch and regional competition for the colonization of all patches. We show that heterogeneity in nutrient availability and limited capacity to disperse seeds mitigate the effect of competition for the local nutrient resource and allow the evolution of lower rates of nutrient uptake. Our spatially explicit model suggests that evolution in richer ecosystems selects "expensive" strategies (high acquisition, but low conservation of resources) compared to poor ecosystems. Low rates of nutrient acquisition can be considered as a form of altruism because they leave more resource available for other individuals. Our model thus suggests that the influence of spatial processes on the evolution of altruism is pervasive and is linked to key aspects of ecosystem functioning. Our work confirms that the interplay between local and regional competition is critical for the evolution of plant nutrient strategies and its effect on ecosystem properties. Our approach could be used to study the evolution of many traits allowing plants to control nutrient availability, e.g. the capacity to control the mineralization of dead organic matter or nitrification. This should be particularly important in the context of global changes because plant reactions to these changes are both ecological and evolutionary.

    Image caption: Grass layer of the savanna in Hwange National Park, Zimbabwe. Photo provided by authors.
    You can read the article in full here.

     

    Defenders in the Tundra: Plant defense is determined by nutrient availability and elevation

    Jonathan R. De Long, Maja K. Sundqvist, Michael J. Gundale, Reiner Giesler and David A. Wardle Photo credit: Paul Kardol.

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    Plants use chemical and structural defense compounds to protect themselves from herbivory and harsh environmental conditions. Many of these compounds also influence decomposition rates in dead leaves and thereby control nutrient cycling and availability. A number of theories predict that alleviating nutrient limitation in the soil, namely nitrogen (N) and phosphorus (P), and reducing other environmental stressors such as harsh climatic conditions, will result in decreased production of plant chemical defenses. Basically, plants will need reduced defense against herbivory and environmental stresses when growing conditions are more favorable. In this study, we measured plant defense properties in both fresh and dead plant leaves in a N and P fertilization experiment set up at each of three elevations in Swedish subarctic tundra heath vegetation. We also measured how responses of defense properties at the plant community level to elevation and nutrient addition were driven by variation within species (i.e., different members of the same species) versus variation among species. We hypothesized that N fertilization would reduce plant defense properties and that this reduction would be greater at higher elevations where nutrients are most limited and climatic conditions are least favorable, while the effects of P fertilization would have no effect at any elevation. Broadly in line with our hypotheses, N fertilization reduced most plant defense compounds in both fresh and dead leaves, while P fertilization had few effects. The effects of N fertilization frequently varied with elevation, but in contrast to our hypothesis, these effects were strongest at the lowest (i.e., warmest) elevation. The effect of N fertilization and its interactive effect with elevation were primarily driven by variation within species, rather than by variation between different species. Our findings suggest that as temperatures warm and N availability increases due to global climate change, defense compounds in subarctic heath vegetation will decline particularly within species. These results highlight the need to consider the effects of both nutrient availability and temperature, and their interaction, in driving subarctic plant defense.

    Image caption: Photo credit: Paul Kardol.
    You can read the article in full here.

     

    Parent-offspring co-adaptation in a wild bird

    Carsten Lucass, Peter Korsten, Marcel Eens, Wendt MüllerBlue tit brood. Photo credit: Wendt Müller.

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    The offspring of many animals depend on their parents’ care (like the provision of food) and have to solicit such care through specific behaviours such as begging, as exhibited by hungry nestlings in birds. Nestlings beg more intensely when they are hungrier, to stimulate their parents to bring more food. When the parents do so, the offspring thus become less hungry and so beg less in turn. Because of the tight interplay between parents and offspring, their behaviours will evolve in order to adapt to each other, leading to ‘co-adaptation’ between parents and offspring. Because behaviours are flexible and parents and offspring continuously respond to each other, it is unlikely that the overall levels of begging and food provisioning are co-adapted; it is more likely that the amounts of change in both the offspring’s begging when they become hungrier and the parents’ provisioning in response to this begging will be co-adapted. Thus, the behavioural responses of parents and offspring may be matched within families. For example, parents that are relatively unresponsive to their offspring’s begging may be better matched with very responsive offspring, because highly responsive parents would overload such responsive offspring with food, rapidly tiring themselves. To test this, we studied wild blue tits. We exchanged same-sized clutches between breeding pairs to disrupt the behavioural match between parents and their offspring. Next, we measured the provisioning responses of parents to changes in food demand of their foster brood (by temporally manipulating their brood size) and the begging responses of the nestlings in relation to different hunger levels. We found the mother’s provisioning and genetic offspring begging were unrelated. However, even though fathers were not raising their own offspring, the provisioning and begging responses of fathers and their genetic offspring (raised by foster parents) were related. Fathers that strongly respond to changes in brood demand have genetic offspring that only show weak begging responses when hungry and vice versa. This is the first study to show the evolutionary interplay between behavioural responses of both parents and offspring. The outcomes are highly relevant for improving theoretical models of parent-offspring co-adaptation.

    Image caption: Blue tit brood. Photo credit: Wendt Müller.
    You can read the article in full here.

     

    The relationship between microhabitat use, allometry, and functional variation in the eyes of Hawaiian Megalagrion damselflies

    Jeffrey Scales & Marguerite ButlerThe eyes of  Megalagrion n. nigrolineatum, an example of a Hawaiian damselfly that breeds along pools.

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    The eyes are our “windows to the world”, but do they match where we live? One of the ways in which animals generate biodiversity is through the process of adaptation, for example when the beaks of birds matches the food type they specialize on. The eyes, while not as well-studied for ecological adaptation as the jaws for feeding or limbs for locomotoion, are particularly interesting because eyes are under a lot of constraints. Fundamentally, larger eyes can see better because larger eyes with larger photoreceptors can collect more light. To produce a finer image, however, requires more photoreceptors viewing the same image. Nowhere are these constraints more obvious than in the eyes of insects, with their modular organization. How this tradeoff is resolved, and how it interacts with size is a very interesting question for visual evolution, and is especially apparent in forest-dwelling flying insects, where the habitat may be dark and variably lit, and insects face additional constraints related to flight. Here we examine how differences in size and habitat use (where they live within the forest) influence the visual design of the eyes of closely related Hawaiian damselflies. While all of the Hawaiian damselflies rely heavily on vision to capture prey and find mates, they live in slightly different habitats within the forest that differ in lighting and complexity. We find that eye size is tightly linked to body size so that larger damselflies have larger eyes. However, other eye traits related to light sensitivity and visual resolution are associated with the “niches” used by damselflies. Because eye design varies with small differences in habitat, species with small eyes should be able to see as well, or better than even the largest Hawaiian damselfly species. Thus, even small species with relatively small eyes can live in dark habitats. These findings suggest that although body size plays an important role in determining eye size, eyes can be fine-tuned to match their different microhabitats, and there is sufficient variation to exploit even small scale differences.

    Image caption: The eyes of Megalagrion n. nigrolineatum, an example of a Hawaiian damselfly that breeds along pools.
    You can read the article in full here.

     

    Glucocorticoid manipulations in free-living animals: considerations of dose delivery, life-history context, and reproductive state

    Glenn T. Crossin, Oliver P. Love, Steven J. Cooke, & Tony D. WilliamsResearchers prepare an adult Atlantic salmon (Salmo salar) for physiological manipulation in order to test predictions regarding individual variation in overwinter migration strategy. Photo by Xavier Bordeleau.

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    Attempts to identify the physiological basis of life-history variation in wild animals often use an experimental increase or blocking of a particular hormone combined with observations of subsequent behaviour, breeding investment (e.g. fecundity, parental care), and survival. Experimental manipulations of ‘stress’ hormones (glucocorticoids - GC) can be very useful, but predicting their effects is often difficult. Much uncertainty can emerge given that GCs possess a dichotomous physiological role: baseline levels regulate daily energy use while higher levels mediate responses to stress. As such, the relative levels that are expressed and their interaction with life stage, ecological variation, age, and sex can differentially impact fitness.

    In this Perspectives piece, we review the literature surrounding GC manipulations, discuss the potential pitfalls when designing GC studies, and make recommendations for how future studies can benefit by considering broader sets of overarching hypotheses. Ultimately, we urge researchers to consider three key points when designing experiments: the life-history context of the species under study (e.g. long- vs. short-lived, reproducing only once or repeatedly, etc.), the ecological context that it is studied in, and the choice of the most appropriate GC dose that will best test the predictions posed by the hypotheses.

    Image caption: Researchers prepare an adult Atlantic salmon (Salmo salar) for physiological manipulation in order to test predictions regarding individual variation in overwinter migration strategy. Photo by Xavier Bordeleau.
    You can read the article in full here.

     

    Evidence of trophic specialization in cave species challenges the usual prediction of generalist feeding in food-limited environments

    Clémentine Francois, Florian Mermillod-Blondin, Florian Malard, Francois Fourel, Christophe Lécuyer, Christophe J. Douady and Laurent SimonSampling of groundwater organisms at Borne aux Cassots cave (France). Photo: Robert Le Pennec.

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    The identification of feeding strategies along a specialist-generalist continuum is fundamental to the understanding of many ecological processes associated with food web structures and ecosystem functioning. Theory states that the amount of food available in a given environment influences these feeding strategies. In food-limited environments, generalist species are expected to occur because species may not be able to subsist when feeding only on a reduced set of food sources. However, species living in these poor environments often exhibit peculiar biological traits, such as improved food-finding abilities or low metabolic rates, which may release the constraints due to low food availability, and allow for specialist species even in these harsh habitats.

    This paper tested this hypothesis of specialist species in food-limited habitats by focusing on two aquatic cave-dwelling water slaters (isopods within the Proasellus genus), as they live in one of the most food-limited environments on Earth. We used carbon and nitrogen stable isotopes (13C and 15N) to quantify the transfers of carbon and nitrogen from each food source to the organism.

    The degree of specialization of these two isopod species was determined in the laboratory by measuring the rate at which they assimilated C and N when being fed separately with one of the 3 food sources available in caves: fine and coarse particulate organic matter (corresponding to fragments of leaves and wood of different sizes) and sedimentary biofilm (corresponding to the conglomeration of microorganisms developed on the surface of sediments). We demonstrated that both species assimilated far more (up to 10 times) C and N from the sedimentary biofilm than from both kinds of particulate organic matter, indicating a high degree of specialization on biofilm.

    In parallel, the actual diets of these isopods were estimated for five populations (= five distinct caves) per species. All isopods fed predominantly on the sedimentary biofilm (representing in average 83 % of the diet), regardless of the population or species considered.

    Our results showed for the first time in cave species a strong trophic specialization on the sedimentary biofilm. This evidence of specialist species in groundwater challenges the traditional view of the selection of generalist species in food-limited environments.

    Image caption: Sampling of groundwater organisms at Borne aux Cassots cave (France). Photo: Robert Le Pennec.
    You can read the article in full here.

     

    Seed transport by physically active animals: farther than we think?

    Casper H.A. van Leeuwen, Rosanne Beukeboom, Bart A. Nolet, Elisabeth S. Bakker, Bart J.A. PolluxCarp in tank. Photo provided by authors.

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    Seeds enable plants to spread within and between patches of suitable habitat. Wind and water often transport ripe seeds to new places. However, also animals can be vectors for seeds: many animals feed on nutritious seeds or fruits, but do not completely digest all the ingested food. Numerous plants produce seeds that can still germinate after multiple hours of retention in the digestive system of animals. In case animals defecate these seeds after they have moved to a new location, plants may spread into new suitable habitat.

    To estimate the impact of this dispersal mechanism on ecosystems, we need to estimate how far animals might be able to transport seeds. This largely depends on how long it takes before an ingested seed is defecated again. This is often determined experimentally by feeding animals with a known quantity of seeds, followed by monitoring seed retrieval over time. However, up until now, almost all these experiments have been performed with animals resting in cages, while animals dispersing seeds in the wild will be actively moving elsewhere by either swimming, walking or flying. We hypothesized that seed digestion in resting animals would be different than in animals engaged in the physical activity involved in moving to new habitat.

    In our study we therefore compared seed retrieval patterns between animals that were resting in a cage, and actively swimming animals. We used common carp as a model species, as fish are increasingly recognized as important seed dispersers in rivers, particularly for plants colonizing upstream habitat. Physically active fish were found to retain ingested seeds for up to two hours longer than resting fish. This implies fish may transport seeds many kilometres further upstream in river systems than previously estimated. We expect that also in other seed dispersing animals physical activity will influence their seed digestion, and emphasize that this should be taken into account when making predictions of the impact of seed dispersal by animals on ecosystems.

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

     

    What can we predict about a forest based on the sizes of its trees?

    Kristina J. Anderson-Teixeira, Jennifer C. McGarvey, Helene C. Muller-Landau, Janice Y. Park, Erika B. Gonzalez-Akre, Amy C. Bennett, Christopher V. So, Norman A. Bourg, Jonathan R. Thompson, Sean M. McMahon & William J. McSheaImage provided by authors.

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    Numerous characteristics of trees vary predictably with trunk diameter. These include height and other dimensions, water use, growth rate, mortality rate, and abundance. The mathematical descriptions of these relationships, known as “scaling relationships”, are broadly useful for understanding forests globally and their role in Earth’s changing climate system. Characterizing scaling relationships and understanding the underlying mechanisms are therefore of great value.

    This study, which was conducted in a forest at the Smithsonian Conservation Biology Institute, Virginia, characterized scaling relationships for a broad suite of tree characteristics. Field measurements were used to quantify how tree height, crown dimensions, water use, growth rate, mortality rate, and abundance related to trunk diameter. To put results from this forest in a global context, corresponding scaling relationships observed in forests throughout the world were reviewed. All of these results were used to evaluate the consistency of observed scaling patterns in forests with the predictions of ecological theory.

    Results show that existing ecological theory had mixed success at predicting scaling patterns in forests. Some tree characteristics, such as height, were relatively well explained by theoretically predicted scaling relationships. However, scaling relationships for some other characteristics, such as growth rate, deviated meaningfully from theoretical predictions, pointing to mechanisms that have not yet been accounted for. Scaling patterns also varied among tree species and were affected by environmental variation. These findings reveal that while existing ecological theory can often provide reasonable approximations of scaling patterns, a more nuanced understanding of scaling in forests will be important to characterize forest structure and function with sufficient precision to address some of the most pressing questions in forest ecology. In particular, a more refined understanding of scaling in forests will be invaluable in the current era of global change, when understanding how forests are changing and interacting with Earth’s climate is important for both forest conservation and climate change mitigation.

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

     

    Big, warm woodlice “chill out”, rather than cross a habitat corridor

    Andrew D. Barnes, Ina-Kathrin Spey, Lena Rohde, Ulrich Bros, and Anthony I. Dell Camera system (left) within the environmental chamber used to film woodlice as they move around an experimental fragmented landscape (right, blue line indicates woodlice trajectories), also seen at the bottom of the filming chamber. Woodlice movement patterns can then be automatically tracked and analysed using automated image-based tracking software.

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    With increasing global temperatures and habitat fragmentation, the question of whether animals will be able to cope with these environmental changes becomes increasingly important. Species are already tracking rising temperatures by moving to cooler latitudes or elevations in order to remain in their preferred temperature ranges. However, the ability of species to do this is hindered by habitat fragmentation. One possible solution is to create dispersal corridors that link habitat fragments, thus allowing animals to move more easily across the landscape. This gives rise to another important question: will changes in temperature alter the way animals use corridors?

    Theory and data suggest that larger and warmer animals should be more active, thus suggesting that larger, warmer animals should encounter habitat corridors more often. To test this, we used novel automated methods to track the movement of different sized woodlice around a fragmented experimental landscape at temperatures ranging from 15 to 25 ºC. By quantifying the movement and behavior of individuals (e.g., mean and maximum body velocity, the proportion of time spent moving, corridor encounter rate), together with overall corridor crossing rates, we were able to isolate the biological mechanisms driving the relationship between body size, temperature, and corridor use.

    Surprisingly, our results showed that warmer and larger woodlice moved more slowly and crossed corridors less often than colder and smaller woodlice. We also found that the woodlice which moved more often crossed habitat corridors less than the less active woodlice. We explain these counterintuitive findings by individual variability in behavioural responses to warming. Our results suggest that individual behaviour plays a key role in determining how animals use habitat corridors, making the story more complicated than might be expected from general theory, such as a general metabolic response to rising temperature. Understanding this story becomes more critical as global temperatures continue to rise and landscapes become ever more fragmented.

    Image caption: Camera system (left) within the environmental chamber used to film woodlice as they move around an experimental fragmented landscape (right, blue line indicates woodlice trajectories), also seen at the bottom of the filming chamber. Woodlice movement patterns can then be automatically tracked and analysed using automated image-based tracking software.
    You can read the article in full here.

     

    Nitrogen saturation in humid tropical forests after 6 years of nitrogen and phosphorus addition: hypothesis testing

    Hao Chen, Geshere A. Gurmesa, Wei Zhang, Xiaomin Zhu, Mianhai Zheng, Qinggong Mao, Tao Zhang, Jiangming MoAn old-growth tropical forest. Photo credit: Yunting Fang.

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    Nitrogen (N) deposition is increasing globally causing N-saturation, where N input to forests exceeds plant and microbial demand. It has been hypothesized that this N saturation will cause increasing N leaching, nitrous oxide (N2O) emission and N transformation rates and cause limitation of other elements. However, this hypothesis has commonly been tested in temperate forests, but it is not well tested in N-saturated tropical forests.

    To test this hypothesis, we measured soil inorganic N, soil N mineralization and nitrification rate, soil N2O emission rate, and nitrate (NO3-) leaching rate in an N-saturated old-growth tropical forest in south China after 6-years of N and phosphorus (P) addition.

    The results showed that N addition indeed caused further N saturation, as indicated by a significant increase in soil inorganic N, N2O emission and nitrate leaching after N addition, however, N addition significantly decreased in situ rates of net N mineralization and nitrification. On the other hand, P addition significantly decreased soil inorganic N concentration, N2O emission and NO3- leaching, but it significantly increased the net rates of N mineralization and nitrification.

    Our study showed that long-term N deposition in tropical forest may not induce N-saturation symptoms as observed for temperate forest, and that P addition can alleviate N-saturation in such tropical systems; hence it provides new insight into the N-saturation hypothesis.

    Image caption: An old-growth tropical forest. Photo credit: Yunting Fang.
    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.

     

    Arboreality and associated gravitational stress on blood circulation have influenced the evolution of tail length in snakes

    Coleman M. Sheehy III, James S. Albert and Harvey B. LillywhiteAn arboreal eyelash viper (Bothriechis schlegelii) resting on a branch in Costa Rica.  Photograph by Coleman M. Sheehy III.

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    Gravity is a pervasive force that can severely affect blood circulation in terrestrial animals, and these effects can be particularly pronounced in tall or long organisms such as giraffes and snakes. Upright postures create vertical gradients of gravitational pressures within circulatory vessels that increase with depth. In terrestrial animals, this pressure potentially induces blood pooling and edema in the lower-most tissues and decreases blood volume reaching the head and vital organs.

    Since their evolutionary origins about 100 million years ago, snakes have diversified into a wide variety of aquatic, burrowing, terrestrial, and arboreal habitats where they experience various levels of gravitational stress on blood circulation. At the extremes, these stresses range from low to none in fully aquatic species living in essentially “weightless” environments, to relatively high in climbing species, especially arboreal forms specialized for climbing trees. As a result, arboreal snakes exhibit many adaptations for countering the effects of gravity on blood circulation, including relatively tight tissue compartments in the tail. However, patterns of tail length in relation to arboreal habitats and gravity have not been previously studied.

    We obtained length data for 226 snake species representing almost all snake families to test the hypothesis that arboreal snakes have longer tails than do non-climbing species. We found that average tail length increased and average body length decreased with increasing use of arboreal habitats and that arboreal snake species had average tail lengths 3–4 times longer than those of non-climbing species. Snakes with longer tails have a higher percentage of elongate blood vessels contained within the relatively tight skin of the tail, which counters blood pooling experienced during climbing. Total body length appears to be constrained in arboreal species, and total body length in adult female arboreal snakes appears to be an evolutionary tradeoff that favors longer tail lengths over maximum production of offspring as arboreal habitat-use increases. Our findings provide evidence that long tails of arboreal snakes function, at least in part, as an adaptation to counter cardiovascular stresses on blood circulation imposed by gravity.

    Image caption: An arboreal eyelash viper (Bothriechis schlegelii) resting on a branch in Costa Rica. Photograph by Coleman M. Sheehy III.
    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 is wood decomposition affected by nutrients in a tropical forest?

    Yao Chen, Emma J. Sayer, Zhian Li, Qifeng Mo, Bi Zou, Yingwen Li, Yongzhen Ding, Xiankai Lu, Jun Wang, Jianwu Tang and Faming WangWood decomposition patterns over time. Photo from Yao Chen.

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    Tropical forests represent a major store of carbon, a large proportion of which is contained in woody plant parts. The decomposition of woody debris plays an important role in the forest carbon cycle, so understanding what controls wood decay will help us determine how much carbon may be released from wood decay in future. Previous research suggests that wood decomposition is regulated in part by the availability of nutrients. This topic has recently received much attention because nitrogen inputs from the atmosphere are increasing dramatically in tropical regions as a result of human activities. To investigate how changes in nutrient inputs will affect the decomposition of woody debris in tropical forests, we conducted a fertilization experiment using branch segments from four common tree species in a lowland tropical forest in China .

    Fertilization with phosphorus increased decomposition rates whereas fertilization with nitrogen had no significant effect. We observed changes in the patterns of nutrient release from the decaying branches that highlight the importance of the balance of nutrients for decomposer organisms. Our results indicate that the decomposition of wood is primarily constrained by phosphorus availability in this tropical forest. Our study suggests that it may be possible to predict decay rates using the ratio of carbon to phosphorus in tropical woody debris. Additional work with more tree species is needed to determine whether the patterns we observed are more generally applicable.

    Image caption: Wood decomposition patterns over time. Photo from Yao Chen.
    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.

     

    Xylem vessel traits tell the timing of leaf emergence and senescence in native and non-native understory species of temperate deciduous forests

    Jingjing Yin, Jason D. Fridley, Maria S. Smith and Taryn L. BauerlePhoto of the common garden at Syracuse University, Photo by Jason D. Fridley.

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    Non-native understory deciduous woody species tend to advance spring leaf emergence and delay autumn leaf fall compared to native species when growing among natives in temperate forests, whereby they can exploit temporally available resources, such as water, nutrients, sunlight and pollinators. This strategy can potentially enhance growth in non-native species, affect their distribution and abundance, and ultimately cause significant changes to native ecosystems. However, prolonged leaf display also subjects non-native species to possible disruptions in their water conducting cells, due to freezing during the periods of increased frost probability in early spring and late autumn, blocking the water-conducting pathway and disrupting normal water transport capacity. Little is known about how non-native understory species are able to maintain normal water transport for leaf display within this context.

    Xylem vessels are long hollow chains of dead cells, and can carry water from roots to leaves in a plant. Earlier spring leaf emergence in temperate deciduous trees has been shown to be related to narrower xylem vessels because narrower vessels are more resistant to freezing-induced disruptions. We examined the xylem vessel traits in different developmental stages of xylem formation, i.e. metaxylem (formed before true wood), earlywood and latewood, across 82 native and non-native understory deciduous woody species common to Eastern U.S. deciduous forests, and monitored their timing of leaf emergence and senescence during 2008-2010 in a common garden.

    We found that compared to the natives, non-native species possessed specific xylem vessel traits that facilitated their tolerance to frost and allowed them to extend leaf display in late autumn, such as larger metaxylem vessels, smaller latewood vessel diameter and a higher proportion of solitary vessels within early- and latewood. In the spring, native and non-native species exhibited similar dates of spring budbreak and leaf emergence, linked to their similar xylem vessel size and vessel area percentage (the proportion of xylem cross section occupied by vessels) within metaxylem and earlywood. Within both groups, species with earlier bud and leaf emergence had a higher vessel area percentage within metaxylem and earlywood, suggesting understory species need sufficient water to support their early spring growth, even at the risk of freezing-induced cavitation.

    Image caption: Photo of the common garden at Syracuse University, Photo by Jason D. Fridley.
    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.

     

    Agriculture increases temporal variability of stream ecosystem functioning

    Mikko Tolkkinen, Heikki Mykrä, Annamari Markkola and Timo MuotkaImage provided by authors.

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    All biological communities exhibit variability over time but increased variability may indicate a disturbed ecosystem, even if species richness and mean rates of ecosystem functions remain unaltered. Most previous studies on temporal variability of biological communities have focused on biomass production, while variability in the rates of other ecosystem functions has gained much less attention. We measured leaf decomposition during three consecutive years in three types of headwater streams: naturally acidic streams, agricultural streams with moderate nutrient enrichment and non-impacted reference streams. Leaf decomposition is frequently used as an indicator of stream ecosystem functioning, based on the rationale that food webs of most headwater streams are fuelled by the autumnal input of leaves from riparian trees. Once in the stream, leaf litter is processed by invertebrates and microbes, particularly freshwater fungi. We surveyed the species composition of fungal decomposer assemblages on submerged alder leaves in all three stream types in each study year to test whether fungal community composition and leaf decomposition rates are more variable over time in human disturbed than in reference streams. Temporal variability of leaf decomposition was indeed higher in nutrient-enriched than in non-modified reference streams whereas human impacted and naturally acidic streams did not differ. Fungal assemblages in both agricultural and naturally acidic streams were strongly dominated by a few key species whereas non-modified reference streams supported communities with more even abundance distributions. Inter-annual variability of leaf decomposition rate was positively related to dominance, with more variability in streams where fungal assemblages were dominated by a few prominent species. Our results show that although the process rates and diversity of fungal communities are regulated partly by the same environmental factors (for example, stream water pH and agricultural nutrient enrichment), processes are more sensitive to human disturbances. We emphasize the importance of measuring not only the mean rates, but also, and perhaps even more importantly, temporal variability of ecosystem process rates in any attempt to assess the influence of human disturbance on ecosystem functioning.

    Image caption: Image 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.

     

    Plasticity in sexual size dimorphism

    Camille Bonneaud, Erin Marnocha, Anthony Herrel, Bieke Vanhooydonck, Duncan J. Irschick and Thomas B. SmithA sagrei Bimini. Image provided by authors..

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    Why do male and female animals differ in body size? Differences between males and females in body size, known as sexual size dimorphism (SSD), is one of the most fascinating and mysterious features of animals. Both different species, and different populations within a species, often vary notably in this feature, but the reasons have remained obscure. Many studies have focused on sexual selection being the primary factor driving variation in SSD. Sexual selection involves the selection of features that help to maximize reproductive success, either by attracting mates, or by outcompeting rivals of the same sex. But another possibility is that variation in resource availability, such as food, could explain much of the variation in SSD. For example, consider two populations that vary in food availability – if males and females differ in how rapidly they grow in response to increased food, then variation in food availability could explain among-population variation in SSD. We tested this hypothesis by integrating laboratory and field studies for different populations of the common Bahamian lizard Anolis sagrei. In this species, males are typically larger than females, but how much they differ varies among different populations. The Bahamas offers a wonderful test case because islands vary in size, which usually correlates with variation in food availability. We first performed laboratory studies which showed that the amount of food had a significant impact on male, but not female, growth. Then, in the field, we showed that the total amount of food biomass within an island explained variation in male, but not female, body size. Our data therefore offer a fairly simple explanation for variation within some species in SSD – namely, the amount of food available to them. This is an alternative view to the common explanation of sexual selection driving variation in SSD. Further, these findings provide support for the condition-dependence hypothesis, according to which the larger sex should display greater plasticity in growth in response to environmental conditions.

    Image caption: A sagrei Bimini. Image 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.

     

    Subordinate plants and fungi: what happens when these minorities join the effort?

    Pierre Mariotte, Bjorn J.M. Robroek, Vincent E.J. Jassey, Alexandre ButtlerImage provided by authors.

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    Drought events are recurrent phenomena, which are predicted to increase over the next few decades. The response of grasslands to drought seems to be determined by both species diversity and community composition. According to the diversity-insurance hypothesis, diverse plant communities have a higher chance of containing species well adapted to drought. Indeed, many experiments have confirmed a positive effect of plant species diversity on community resistance to drought, but the underlying mechanisms remain unknown.

    In parallel, the subordinate insurance hypothesis suggests that highly diverse communities contain higher number of subordinate species, which are more resistant than dominant species to climate change conditions and can compensate for less resistant species. Earlier, it has been reported that subordinate species can improve grassland productivity during drought but, surprisingly, these species seemed not to possess a better physiological ability for water use efficiency. Therefore, we hypothesized that their role might be better found belowground.

    Using a combination of subordinate species removal and summer drought in grassland, we show that soil processes play a critical role in the community resistance to drought. Our results highlight that subordinate species shift the balance within the soil microbial community towards more fungal dominance. Fungal communities, promoted by subordinate species, were more resistant to drought and maintained higher rates of litter decomposition and soil respiration. These results emphasize that subordinate species play an important role in mitigating drought effects on soil ecosystem functions. Reciprocal effects between fungi and subordinate species explain also how subordinate species better resisted drought conditions.

    Our findings highlight interesting plant-soil feedback effects between subordinate species and fungi, which seem delayed in time following a perturbation. Indeed, we showed plant effects on soil under ambient precipitation, with subordinate plant species favoring fungal communities, followed by soil effects on plants under drought conditions, with more resistant fungal communities being able to improve the resistance and growth of subordinate species. Additionally our results extend the diversity-insurance hypothesis by showing that more diverse communities not only contain species well adapted to perturbations, but also species with higher impact on soil microbial communities and related ecosystem functions.

    Image caption: Image 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.

     

     

    Birth date predicts alternative life history pathways in a fish with sequential reproductive tactics

    Teresa Fagundes, Mariana G. Simões, João L. Saraiva, Albert F. H. Ros, David Gonçalves and Rui F. OliveiraThe two alternative male morphotypes of the peacock blenny: bourgeois nest-holders (front) and parasitic female mimics (back).

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    In some species individuals of the same sex, usually males, can reproduce by adopting different behaviours, depending on factors such as body size. In this paper we studied the factors that determine the alternative mating tactics that males can adopt in a littoral fish, the peacock blenny (Salaria pavo). In this species two mating tactics occur: (1) larger males defend nests in crevices to which they attract gravid females to mate with; after spawning nest-holder males provide parental care to eggs until they hatch; (2) smaller males do not express the ornaments of males and instead mimic females, both morphologically and behaviourally, in order to get access to the nests defended by nest holders, and to sneak fertilizations. Here we report a long term (6 years) mark–recapture study, which demonstrated that these alternative reproductive tactics are sequential, that is younger and smaller males may act as sneakers but as they grow older and larger all behave as nest-holders. We also found that males may follow different developmental trajectories depending on their date of birth. Males born earlier in the breeding season get to their first breeding season with a larger size than males that born later in the season. Accordingly, the former express the nest-holder tactic from their first breeding season onwards, whereas the later reproduce in their first breeding season as sneaker males and subsequently switch to nest-holders. The occurrence of a birth date effect on the expression of alternative reproductive tactics leaves room for important parental effects that should be investigated in future studies.

    Image caption: The two alternative male morphotypes of the peacock blenny: bourgeois nest-holders (front) and parasitic female mimics (back).
    You can read the article in full here.

     

    An invasive plant evolves rapidly in response to changes in climate

    Ferran Colomer-Ventura, Jordi Martínez-Vilalta, Paolo Zuccarini, Anna Escolà, Laura Armengot and Eva Castells Plants at their native area in South Africa (left) grow under wetter and hotter conditions than those introduced into novel regions, for example Australia (right). Differences in climate are driving a rapid evolution of this invasive species. Pictures: Eva Castells.

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    Biological invasions are one of the largest problems affecting biodiversity at a global scale. The study of invasive species, however, can also provide us with information on the response of organisms to a changing environment. Current hypotheses predict that invasive plants can rapidly evolve when they encounter new environmental conditions. Contemporary adaptation, which is revealed by different plant characteristics in the native and invasive plants, could facilitate the invasion process. Here we have evaluated how invasive plants respond to simultaneous changes in climate and herbivory.

    Senecio pterophorus is a shrub from the daisy family native to the Eastern Cape in South Africa. This species was accidentally introduced into the Western Cape in South Africa, Australia and Europe 40-100 years ago. In their native habitats plants are subject to wetter and hotter summers than those in the introduced areas. Additionally, native plants are more attacked by herbivores than their invasive counterparts. All these differences could lead to changes in plant morphology after invasion.

    Seeds collected from the native and the three non-native regions were grown in an experimental field under similar environmental conditions. We had two objectives. First, we aimed to determine whether plants from different origins were genetically distinct for some traits related to plant performance, such as growth, leaf area or reproductive capacity. Second, we aimed to determine whether climate and herbivory measured at the collection sites played a role in this genetic differentiation.

    Plants from the non-native regions were smaller and had a lower reproductive output than plants from the indigenous area. Herbivory was not related to these changes in plant traits. In contrast, our results are consistent with the role of climate driving rapid evolution of the non-native plants. Understanding the mechanisms for rapid differentiation in response to novel climatic conditions improves our ability to explain the dynamics of biological invasions and also to predict the response of native populations under a climate change scenario.

    Image caption: Plants at their native area in South Africa (left) grow under wetter and hotter conditions than those introduced into novel regions, for example Australia (right). Differences in climate are driving a rapid evolution of this invasive species. Pictures: Eva Castells.
    You can read the article in full here.

     

    Wood mice select foraging site according to the extent of within-plant variability in seed characteristics

    Takuya Shimada, Akiko Takahashi, Mitsue Shibata, and Tsutomu YagihashiThe Japanese wood mouse, endemic to Japan, is a major consumer of acorns. When they found acorns, they carry and hide them mostly in the ground or under fallen leaves for future use. Photograph credit: Y. Suzuki.

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    In general, foods are not uniformly distributed for animals, but distributed patchily in their home range. In this situation, animals have to evaluate the quality of foraging patches and select one for foraging. An oak tree, for instance, forms a foraging patch for seed-eating rodents, where acorns (seeds of oaks) are the food resource. Characteristics of these resources often vary largely even within a foraging patch (an individual plant), which is known as within-plant variation. In such a case, how does the animal evaluate the quality of patches? One of the simple and widespread ideas is using the mean as a representative. Namely, the quality of a patch is defined as the mean of the quality of each resource (acorn), such as acorn weight or nutritional value. However, patches with the same mean but different variation may not be equal for animals. To best describe the quality of a patch, within-plant variation must be considered in addition to the mean values.

    In this study, we examined which trees the Japanese wood mouse (Apodemus speciosus) would select as a foraging patch for acorns of konara oak (Quercus serrata). Here, the mean, variance (spread of values), and skewness (tendency to extreme values) of within-plant distributions of two acorn characteristics (weight and tannin content) were used as indicators of the quality of patches, and we examined the relationships between these indicators and patch selection by the wood mouse. Tannins are a bitter tasting chemical, and most animals tend to avoid tannin-rich food.

    There was notable within-plant variation in acorn weight and tannin content, and significant among-individual variation was also observed. We found that wood mice preferred to forage beneath trees with a large mean and variance of seed weight and a small variance and skewness of tannin content. These findings highlight that, in order to understand ecological and evolutionary processes at work in plant-animal interactions, within-plant variation in seed characteristics must be considered as well as mean value.

    Image caption: The Japanese wood mouse, endemic to Japan, is a major consumer of acorns. When they found acorns, they carry and hide them mostly in the ground or under fallen leaves for future use. Photograph credit: Y. Suzuki.
    You can read the article in full here.

     

    Mechanisms and consequences of facilitation in plant communities

    A portfolio effect of shrub canopy height on species richness along a competitive stress gradient

    Kari Anne Bråthen and Christopher LortieImage provided by authors.

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    Biodiversity is a critical resource in ecosystems both ecologically and economically for humans. It is thus a pivotal challenge for ecologists to explain and predict the biodiversity of any given ecosystem. In this study we focus on how the biodiversity of plants in tundra ecosystems can be facilitated. In tundra ecosystems plants are exposed to low temperatures and strong winds and on top of this the plants are grazed by herbivores. Consequently, the presence of dominant tundra shrubs with woody canopies can facilitate other plant species to cope with both stressful environments and presence of herbivores. These shrub canopies protect against grazing and wind abrasion, provide a protective snow layer in winter, trap particles and seeds for soil formation and new species establishment in summer, and buffer against temperature extremes. We propose that this range of positive mechanisms be termed “a portfolio effect of shrub canopy height”, and thus that the presence of higher shrub canopies increases biodiversity. We find support for our prediction. Along the entire gradient from low productivity, stressed plant communities to higher productivity, more competitive communities, we find that greater shrub canopy height promotes biodiversity. More particularly we find shrub canopy height to promote biodiversity on top of a humped-back relationship between biodiversity and plant productivity (i.e. at low and high productivity levels biodiversity is low and at intermediate productivity levels biodiversity is high), and as such we also find support for a general theory explaining biodiversity, i.e. the humped-back relationship. Climate change is currently causing encroachment of shrub species into tundra ecosystems. This study suggests that a universal theory of biodiversity is at play also in tundra plant communities, and that shrub dynamics are a crucial additional element in understanding changes in tundra plant biodiversity. It is thus likely that including the presence and height of shrub dominants will improve predictive models of biodiversity.

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

     

    Stress, immunity, and energy use in snakes

    Lorin A. Neuman-Lee, H. Bobby Fokidis, Austin Spence, Marilize Van der Walt, Geoffrey D. Smith, Susan Durham, and Susannah S. FrenchA male Terrestrial Gartersnake (Thamnophis elegans).

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    Wild animals undergo resource limitations throughout their lives, and must allocate this limited energy to a variety of physiological functions, such as growth, response to stress, and immune functions. In infrequent feeders, such as many snakes, shorter term limitations may not be as critical. Stressors, commonly experienced by wild animals, can also affect resource allocation “decisions” when energy is limiting. When an animal experiences stress, adrenal steroid hormones (such as cortisol in humans) are released into the bloodstream. These hormones have many functions, but chiefly mobilize energy for use in the body. When an animal is chronically stressed, it may be continuously secreting these hormones and therefore mobilizing energy. This energy usage may become detrimental, especially if no new sources of energy are available.

    The objective of this study was to determine how infrequent feeders, such as gartersnakes, are affected by chronic stress and food restriction. We restricted food for six weeks in half of the animals in the study and chronically stressed half of the animals (half food restricted and half not) using restraint stress. At the end of the experiment, we measured energy metabolites (triglycerides, glycerol, protein, and ketone) and compared the metabolite levels to two physiological measurements (immune and stress response). Food restricted animals did not lose significant amounts of body weight over the six week period, but did have altered levels of the energy metabolites triglyceride and glycerol. Also, chronically stressed animals responded by releasing significantly greater amounts of adrenal steroid hormones during acute stress than animals not chronically stressed. Finally, chronically stressed snakes had a reduced ability to heal wounds and a combination of both food restriction and chronic stress resulted in suppressed innate immune function. This study provides evidence that energetic limitation and stress can result in interactive and dramatic changes in energy usage and storage as well as in physiological functions that are critical to maintain life.

    Image caption: A male Terrestrial Gartersnake (Thamnophis elegans).
    You can read the article in full here.

     

    Preferred nest-sites help female song sparrows successfully raise chicks in early spring conditions

    Ryan R. Germain, Richard Schuster, Kira E. Delmore, and Peter ArceseFemale song sparrow searching for nesting material. Photo credit: Sylvain Losdat.

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    Choosing the right location to raise offspring can have important consequences for an individual animal’s overall reproductive success. For North American songbirds that build open-cup nests in the potentially harsh conditions of early spring, breeding in higher quality habitat can reduce some of the costs associated with producing and caring for their young. With the potential hazards of early spring breeding like cold temperatures and heavy rainfall, come the rewards of greater offspring survival and more future nesting opportunities for the parent. Thus, any advantages available to breeding birds during this crucial reproductive stage could lead to important benefits over both the entire year, and their lifetimes.

    We used 38 years of nesting records from an island song sparrow (Melospiza melodia) population to determine the relative influences of preferred, high-quality nest-sites on early spring reproductive success. We found that females that used these preferred sites tended to lay their eggs earlier in the season, incubated their eggs more efficiently, and produced chicks that were more likely to survive and become breeders in the population the following year. We also investigated potential cues (relative warmth and food availability) by which female sparrows may select early season nest-sites. Preferred nest-sites were relatively cooler overall, likely due to greater vegetation cover than less-preferred sites, but also had indicators of greater caterpillar abundance, a key food source during the early spring. Our findings show that breeding in preferred, high-quality habitat may offer female sparrows a reproductive advantage by allowing them to produce and care for their young at a lower energetic cost to themselves. These results provide clear evidence of the importance of habitat quality on the success of animals living in seasonal environments.

    Image caption: Female song sparrow searching for nesting material. Photo credit: Sylvain Losdat.
    You can read the article in full here.

     

    Moving Beyond Body Condition Indices as an Estimate of Fitness in Ecological and Evolutionary Studies

    Shawn M. Wilder, David Raubenheimer and Stephen J. SimpsonCallipers used for measuring. Photo provided by authors.

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    Ecologists, physiologists and evolutionary biologists are often interested in measuring the state or condition of animals. One shortcut that has been taken to estimate condition is the use of body condition indices, which measure the mass of an animal relative to frame or skeleton size. For example, in humans, the Body Mass Index (BMI; mass / height2) has been used as a body condition index. However, BMI is only a coarse measure of body composition and people with the same BMI can have very different body composition (e.g., weight lifter vs. obese person). Similarly, body condition indices used in ecological and evolutionary studies of a range of other animals are coarse or poor estimates of body composition (e.g., the relative amounts of lipid, protein and other components of the body). Another problem with body condition indices is that they are often used as a surrogate for body lipid content. The lipid content of an animal can be important for health or fitness but there are many other characteristics that could also be related to health. Furthermore, high body condition values are often assumed to reflect high health or fitness. However, as we know from studies of humans, individuals with intermediate condition index values may have higher health or fitness than individuals with very high (e.g., obesity) or low (e.g., malnutrition) values.

    As a consequence of these problems with condition indices, we argue that biologists should abandon body condition indices in favor of more descriptive or detailed measures of the physiology or composition of animals. Methodological advances have resulted in a range of techniques to accurately measure many aspects of animal physiology and composition, including many noninvasive techniques. For example, in humans and many other animals, dual-energy x-ray absorptiometry can be used to provide an accurate and noninvasive measure of body lipid, lean mass and skeleton content. More accurate data on animal physiology and composition will provide us with a better understanding of the ways in which animals respond to their environment and the connections between behavior, physiology and ecology.

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

     

    Jack of all foods or master of one: symbiotic bacteria determine the diet of an insect pest

    Steven M Wagner, , Adam J. Martinez, Yong-ming Ruan, Kyungsun L. Kim, Paul A. Lenhart, Allison C. Dehnel, Kerry M. Oliver, and Jennifer A. WhiteColony of Aphis craccivora infesting young locust tree (Robinia pseudoacaciae). Image provided by authors.

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    Unseen microbes can affect the patterns observed at the macroscopic level in nature, mediating ecological interactions among plants and animals. Many herbivorous insect species are found to feed on multiple plant species, yet individual insects often perform well on only a subset of these plant species. Because infection with specific microbes often correlates with the use of particular plants, there has been much speculation, yet limited experimental evidence, that microbes promote dietary specialization. Here we investigated whether bacterial symbionts influence the diet of the cowpea aphid, which feeds on diverse plant species, including economically important crops. We first show that cowpea aphid clonal lines, each isolated from a single female, vary in their ability to use different plant species, which in turn correlates with patterns of infection by particular maternally-inherited bacteria. We next focused on aphid clones that naturally performed better on locust trees than other plant species, and which were infected with a common insect symbiont called Arsenophonus. We used antibiotics to remove Arsenophonus from two aphid clones and found that elimination of this symbiont dramatically reduced performance on locust, while generally increasing performance on other plant species. In fact, the uninfected aphids from "locust-specialist" lines didn't perform any better on locust than alfalfa-specialist lines, indicating that the bacteria are a critical component for effective use of locust as a food plant. We also experimentally infected an alfalfa-specialist aphid line with Arsenophonus, which instantaneously improved aphid performance on locust and decreased performance on alfalfa, effectively transforming an alfalfa specialist into a jack-of-all food plants. Inherited bacteria, including Arsenophonus, are widespread in insects and periodically gained or lost by host insect lines through natural processes; our results show that such transitions can abruptly change the food plant range of an herbivore, either restricting or facilitating use of particular plant species. If these changes improve performance on economically important food plant species, inherited microbes have the potential to transform innocuous herbivores into pests of consequence.

    Image caption: Colony of Aphis craccivora infesting young locust tree (Robinia pseudoacaciae). Image provided by authors.
    You can read the article in full here.

     

    Perspective

    Does history matter in plant interactions?

    Susanne Wurst &Takayuki OhgushiMultiple interactions including galling midges, aphids, and ants on a willow, Salix eriocarpa.

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    Plants interact with a wide range of organisms above and below the ground. These spatially separated organisms can indirectly affect each other through changes in plant characteristics which do not stop at the plant level, but can also affect the zones of influence of the plants both above (the ‘phyllosphere’) and below ground (the ‘rhizosphere’).

    Here, we ask if biotic interactions of plants below- and aboveground can have long-term legacy effects on future biotic interactions. In other words: does the history of biotic interactions matter for future biotic interactions of plants?

    We propose that history (or legacy) effects are mainly transferred by changes in plant and/or soil characteristics. Changes in plant and soil characteristics caused by biotic interactions such as feeding on plant materials can be short- or long-term. For example, plants can react with a rapid defense response against feeders that often vanishes when the feeding ceases. This is seen as a short-term response. On the other hand, plants can also invest in new leaves or roots to compensate for feeding damage or translocate nutrients to unattacked plant parts. These are more long-term changes and are more likely to persist and affect future interactions of plants. In soil, carbon input into the rhizosphere can be changed in the short term and affect the activity of the microbial community in the rhizosphere, while litter quality changed by feeding may affect decomposition and soil biota communities in the longer term. We also ask about the potential consequences of long-term and history effects in terrestrial ecosystems. The fitness of plants, the composition of biotic communities and the functions of ecosystems may all be affected by past biotic interactions. We conclude that the history of past interactions should be included in studies on biotic interactions for a better understanding of the current community organization.

    Image caption: Multiple interactions including galling midges, aphids, and ants on a willow, Salix eriocarpa.
    You can read the article in full here.

     

    The double-edged sword of immune defence and damage control: Do food availability and immune challenge alter the balance?

    Zachary R. Stahlschmidt, Madison Acker, Ilya Kovalko and Shelley A. AdamoFemale Texas field cricket. Photograph by ZRS.

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    Although immune resistance is necessary to kill pathogens, it may also cause damage to hosts. Thus, animal immune systems must adaptively balance aggressive immune resistance (ability to destroy pathogens) with infection tolerance (ability to withstand the self-damage caused by immune resistance). Insects offer unique insight into this balancing act because phenoloxidase (PO)-mediated melanisation is a key feature of immune resistance, but PO activation causes inevitable self-damage. The antioxidant glutathione (GSH) may reduce this damage, but high levels of GSH can impair melanisation. We first showed that GSH may be a mechanism of infection tolerance because GSH levels in crickets correlated with fecundity (egg-laying) despite bacterial growth—that is, crickets with high levels of GSH in their hemolymph (blood) were able to maintain reproductive output despite increased levels of bacterial infection. Next, we used crickets to examine whether the relative balance between a component of immune resistance (i.e., PO) and protection from self-damage (i.e., GSH) shifted due to food availability or immune challenge. Although GSH and PO were positively correlated with one another, the PO:GSH ratio was robust and not affected by food availability or immune challenge. Thus, increased investment in a mechanism of immune resistance may require an increase in GSH to reduce self-damage (i.e., increase infection tolerance). Chronic immune challenge led to greater tolerance of oxidative stress suggesting that repeated immune challenge up-regulates infection tolerance mechanisms. Food limitation led to reduced PO activity, but not GSH concentration. This result suggests that mechanisms of immune resistance may be more sensitive to food availability than mechanisms of infection tolerance. In sum, mechanisms of immune resistance and infection tolerance can be correlated, and they can be affected by food availability or immune challenge.

    Image caption: Female Texas field cricket. Photograph by ZRS.
    You can read the article in full here.

     

    Darwin’s dream: a manipulative experiment for measuring natural selection in animal populations

    José Luis Bartheld, Juan Diego Gaitán-Espitia, Paulina Artacho, Cristian Salgado-Luarte, Ernesto Gianoli and Roberto F. NespoloImage provided by authors.

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    Natural selection is one of the most important ideas in the history of science, but for a long time, testing it experimentally was elusive. As Darwin thought, natural selection was supposed to be too subtle to be accurately measured. However, ecologists and evolutionary biologists have shown that rapid evolution is commonplace, and that applying the appropriate procedures (e.g., using closed system such as islands, applying reciprocal transplant experiments) both the magnitude and shape of selection could be measured with precision.

    In order to characterize fitness profiles –that is, the shape of selection- individuals in animal populations need to be marked, measured and recaptured. We chose to do such an experiment with the garden snail, an animal easy to collect in large numbers and also easy to mark and recapture. Also, it is distributed over a broad geographic range.

    We tested one of the most important tenets of physiological ecology (and the one that shaped its development during the eighties and nineties): the assumption that energy allocation in organisms and populations is adaptive (i.e., a target of natural selection).

    To do this, we performed a reciprocal transplant experiment using distant populations, which were bred in captivity and then released (about 1500 snails) at both extremes of their range, 1300 kms apart. Before release, we measure a suite of physiological, morphological and life-history traits.

    Our results were surprising. The results in general are not consistent with the occurrence of local adaptation (i.e., higher fitness at home), and in spite of the very different climates of the original populations, we found that only two traits (energy metabolism and body size) were the target of selection. This strikingly homogeneous result suggests that some general rule for adaptive optimization exists in these snails.

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

     

    Neighbour presence reduces root allocation

    Bin J. W. Chen , Heinjo J. During, Peter J. Vermeulen, Hans de Kroon, Hendrik Poorter and Niels P. R. AntenTwo split-root pea plants sit on the edges of two pots and place their roots in both pots. Thus, each plant has access to the volume of two pots, and share soil nutrients with the neighbour.

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    Increasing evidence suggests that plants are able to detect the presence of belowground neighbours. Such detection allows them to change their investment strategies in root growth and seed production. However, there is a debate about the direction and extent of the associated changes. Several studies propose that plants should grow more roots even at the expense of seed production to defeat their opponents (neighbours). Evidently such findings would have large significance for agriculture where maximum seed production is often the objective. Yet, studies that documented these effects are confounded by the fact that pot volume and plant size were insufficiently accounted for.

    We developed an experimental approach in which the effects of neighbour presence and the effects of rooting volume and plant size are disentangled. We grew pea plants in the presence or absence of a belowground neighbour at a range of soil volumes, while providing equal amount of nutrients per plant. Then, we used a statistical approach that accounts for plant size, rooting volume and neighbour presence effects. We found pea plants were smaller and had less roots in the presence of a neighbour, which contradicts the above-mentioned results and suggests that neighbour-induced root overproliferation did not occur in our study.

    More broadly our results indicate that if the effects of rooting volume and plant size are not taken into account, the effect of neighbours on plant growth can be misinterpreted. Our results do help to reconcile various results of neighbour effects published in the literature, by reasoning what the effect of rooting volume would be in other published studies.

    Image caption: Two split-root pea plants sit on the edges of two pots and place their roots in both pots. Thus, each plant has access to the volume of two pots, and share soil nutrients with the neighbour.
    You can read the article in full here.

     

    Burn or rot: leaf traits explain why flammability and decomposability are decoupled across species.

    Saskia Grootemaat, Ian J. Wright, Peter M. van Bodegom, Johannes H. C. Cornelissen and William K. CornwellThe ignition of a leaf. Photo credit: S. Grootemaat.

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    When leaves fall from a tree basically two things can happen: the leaves will either be decomposed by soil organisms or, in fire prone areas, the leaves can burn in a wildfire. Different plant species have different leaf characteristics. It is generally accepted that leaf characteristics, like lignin and phosphorus-concentrations, drive the speed of the decomposition process. This means that some species have leaves that decompose faster than others, depending on their physical and chemical characteristics. In contrast, less is known about the effects of leaf characteristics on leaf flammability. In this study on 32 species from eastern Australia we investigated which leaf characteristics determine the flammability of species. Both leaf dimensions and chemistry affected the ease of ignition and the burning time of individual leaves. For example, species with thinner leaves or leaves consisting of less dense material ignited more quickly. Leaves with higher moisture content took longer to ignite. Species with large, heavy leaves burned for longer than smaller (light) leaves. Furthermore, species with higher nutrient concentrations had shorter flame durations, suggesting that nitrogen and phosphorus work as flame retardants.

    When we compared the sets of leaf characteristics driving decomposability and flammability respectively, we found no relationship between the two litter fates. This means that leaves that decompose quickly are not necessarily those that are most likely to burn or burn quickly. This study gives us important information because knowing which plant species (and leaf characteristics) make the vegetation more flammable, either directly or indirectly through litter accumulation as a consequence of slow decomposition, can inform fire behaviour models. The results can help to predict where a fire is likely to start and, once a fire has started, some estimates can be made of the likely fire intensity and spread. This can help policy makers, fire fighters and residents to make better informed decisions.

    Image caption: The ignition of a leaf. Photo credit: S. Grootemaat.
    You can read the article in full here.

     

    Food availability and seasonal reproductive activation in a songbird

    Scott Davies, Thomas Cros, Damien Richard, Simone L. Meddle, Kazuyoshi Tsutsui, and Pierre DevicheAn Abert’s Towhee. Photograph by Christofer Bang.

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    Many animals have an outstanding ability to forecast when they need to be in breeding condition, yet much remains to be learned about how they achieve this. Most temperate zone songbirds, in particular, have to be exceptional forecasters because their reproductive system is shutdown during the winter and, to be able to breed, must be activated in the spring. Activation involves dramatic rises in the secretion of reproductive hormones and gonadal growth. This process takes time, so songbirds need to start it well before they need to breed and use cues from the environment that forecast when suitable environmental conditions are approaching. For decades, scientists have recognized that food availability is important because seasonal reproductive activation takes longer if birds are energetically constrained. However, our understanding of the physiological mechanisms that link food availability to activation of the reproductive system is limited.

    To address this issue, we food-restricted captive adult male Abert’s Towhees, Melozone aberti, during reproductive activation. We investigated whether energy deficiency constrains multiple aspects of reproductive activation, in particular the growth of the testes. Since testis growth is the culmination of an endocrine cascade that begins in the brain, we also aimed to understand which steps of this cascade are affected by energetic constraint and, to do so, measured endocrine activity at all three points of this cascade (i.e., brain, anterior pituitary gland, and testes). Consistent with the majority of studies in songbirds, we found no effect of food restriction on testis growth. However, food restriction influenced plasma levels of hormones from all levels of the cascade responsible for reproductive activation.

    These results suggest that energetic constraint modulates reproductive activation not through changes in the growth of the testes, but through changes in the plasma levels of hormones. In other words, even when constrained by energy deficiency, male songbirds can morphologically enter breeding condition, but delay increasing reproductive endocrine activity. This delay may be beneficial as it presumably decreases the expression of energetically costly behaviors, such as aggression and singing, which are stimulated by reproductive hormones.

    Image caption: An Abert’s Towhee. Photograph by Christofer Bang.
    You can read the article in full here.

     

    Does size really matter in predicting bite force in bats?

    Juliana Senawi, Daniela Schmieder, Björn Siemers and Tigga Kingston Juliana Senawi with bats great and small from the study site, Krau Wildlife Reserve, Malaysia. At around 200 g, Cheiromeles torquatus or the Naked Bat is recognized as the largest insectivorous bat in the world, while Kerivoula intermedia or the Small Woolly Bat weighs a mere 3 g (less than a sheet of an A4 paper!!) and is one of the very smallest.  Photograph by Nurul Ain Elias.

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    Would you rather be bitten by a big dog or by a small dog? Neither, of course, but if you had to choose, which one would it be? According to researchers, bite force (bite strength) increases with size in most animals, so the small dog is likely the better bet! Previous research in South and Central America indicates this relationship holds in bats too – bigger bats bite harder than smaller bats. We wanted to test whether this was the case in Asian forests, where the bat fauna is equally diverse, but dominated by very different families of bats.

    So how do we measure how hard an animal bites without losing any fingers? The bats were encouraged to bite a pair of metal plates hinged at one end by a transducer, which converts the pressure of the bite to a readable output of the force. We recorded the maximum bite force and measures of size (body mass, forearm length, head width, head height and head length) of 35 insect-eating bat species captured in Krau Wildlife Reserve, Malaysia. The bats ranged in size from 3 g to 200 g and belonged to 7 families. We also measured jaw features responsible for generating bite force using museum specimens of the same species, and used these to calculate the mechanical advantage (jaw effectiveness) adjusted by the size of the species.

    So, did bigger bats bite harder? The answer was yes, but the relationship between size and bite force differed among the bat families. The effectiveness of the jaw (mechanical advantage) also played a role, regardless of the size of the bat. All 35 species of bats in this study eat insects in the same forest, so they have developed strategies to avoid competition. Having a different bite force than your neighbour may be one – while some species may focus on hard crunchy prey like beetles, others may specialize on softer fare like flying termites and moths.

    Image caption: Juliana Senawi with bats great and small from the study site, Krau Wildlife Reserve, Malaysia. At around 200 g, Cheiromeles torquatus or the Naked Bat is recognized as the largest insectivorous bat in the world, while Kerivoula intermedia or the Small Woolly Bat weighs a mere 3 g (less than a sheet of an A4 paper!!) and is one of the very smallest. Photograph by Nurul Ain Elias.
    You can read the article in full here.

     

 

Cane toad impacts native species reproduction

Edward J. Narayan, Tim S. Jessop and Jean-Marc HeroCane toads present within terrestrial breeding habitats of the endangered Fijian ground frogs (Photograph by Dr Edward Narayan).

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Invasive species, major drivers of global change, cause unprecedented impacts on biodiversity. Their influence is most apparent on small oceanic islands where invasive species are the main cause of extinction. Understanding the mechanisms that make invasive species devastating is central to addressing their ecological impacts on the islands. One idea is that colonization of “simple” small islands affords invaders greater capacity to diversify and intensify their ecological roles beyond those seen in their native or invaded continental distributions.

Here, we used natural and manipulative field experiments to test if density-mediated competitive interactions from the highly-invasive cane toad could cause indirect effects and fitness loss to a small island population of the endemic and endangered Fijian ground frog. Over 13 successive monthly field surveys we collected 5000 non-invasive urine samples and measured body condition, survival and reproductive success of the Fijian ground frog. Samples were then analysed for reproductive and stress hormones. These data provided detailed accounts of how exposure to high-densities of cane toads caused major alterations in the nutritional status, physiological stress and reproductive physiology of ground frogs in both field enclosures and natural habitats. Most telling was that ground frogs in high toad density enclosures experienced extremely poor breeding success.

Despite a wealth of knowledge on the cane toad’s ecological consequences in invaded continents, such as Australia, our results reveal them to have extremely novel ecological roles and consequences on islands. Clearly, our results demonstrated how invasive cane toad competition, through extremely strong indirect effects, triggers major physiological changes that led to the reproductive collapse in Fijian ground frogs. Further, our study suggests it is important to limit alterations to island habitats to reduce the strength of invader-native species interactions. Thus, our results provide a striking example of why invasive species can disproportionately impact island endemics to potentially increase extinction risk.

Image caption: Cane toads present within terrestrial breeding habitats of the endangered Fijian ground frogs (Photograph by Dr Edward Narayan).
You can read the full article here.

 

Prey density and distribution drive the three-dimensional foraging strategies of the largest filter feeder.

Jeremy A. Goldbogen, Elliott L. Hazen, Ari S. Friedlaender, John Calambokidis, Stacy L. DeRuiter, Alison K. Stimpert, and Brandon L. SouthallPhoto by Ari Friedlaender under NMFS Permit: #14534-2.

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Predators use a suite of foraging strategies to maximize their energetic gain and support their metabolism. Foraging in aquatic vertebrates can be broadly categorized into particulate feeding, where single prey items are seized and ingested, and bulk-filter feeding that involves the capture and processing of large volumes of prey-laden water. Several animal groups have independently evolved a bulk-filter feeding strategy, including cartilaginous fish (e.g. whale sharks and basking sharks) and baleen whales. Many filter feeders exhibit a ram-feeding mode where animals use their forward locomotion to drive water into the mouth where filtration occurs.

Large bulk filter feeders have long been assumed to be indiscriminate "vacuums" of the ocean, slowly filtering water regardless of variation in prey distribution, but here we reveal tremendous plasticity of foraging strategies in the world's largest filter feeder, the blue whale (Balaenoptera musculus), which is strongly a function of prey density and depth. Blue whales exhibit a unique mode of ram feeding called lunge feeding which involves the intermittent engulfment of large volumes of prey-laden water that are commensurate with the whale’s body size. Lunge feeding is a high-drag, high intake filter feeding strategy that requires high prey density for energetically efficient foraging.

We simultaneously measured whale foraging behavior and the characteristics of their sole prey resource, krill. Our analyses found that blue whales exhibit much more acrobatic lunge feeding events when foraging on small, low-density, more patchily distributed krill. In contrast, when foraging on dense, deeper, and larger krill aggregations, blue whales increased lunge frequency and maneuvered less during each lunge. These data demonstrate a previously unrecognized range of adaptable foraging strategies in a large bulk-filter feeder. Because maneuvering and diving require significant amounts of energy, the variation in foraging behavior that we revealed has major implications for optimal foraging and bioenergetic models.

Image caption: Photo by Ari Friedlaender under NMFS Permit: #14534-2.
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.

 

Links between metabolic rates and growth depend on food availability.

Sonya K. Auer, Karine Salin, Agata M. Rudolf, Graeme J. Anderson, and Neil B. MetcalfePhoto of brown trout. Copyright Sonya Auer.

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Metabolic rates determine the energetic cost of living and can differ dramatically between individuals. At the very minimum is an individual’s standard (or resting) metabolic rate (SMR) – the energy it must expend on the maintenance of tissues and bodily functions needed to sustain life. Metabolic rates are thought to have important impacts on fitness, but results thus far are equivocal. Some studies find a negative while others find a positive correlation between SMR and different measures of fitness such as growth and survival. These inconsistencies might arise because links between metabolism and fitness depend on environmental conditions. Consideration of an individual’s aerobic scope (AS), in addition to its SMR, might also improve our understanding of the links between energy metabolism and fitness. Aerobic scope (the difference between SMR and maximal metabolic rate – after exhaustive exercise) determines the extent to which an individual can increase its metabolic rate above SMR to finance key functions such as digestion, locomotion, growth and reproduction.

We examined the links between individual variation in both SMR and AS and growth rates of brown trout (Salmo trutta) under different levels of food availability. We measured the SMR and AS of 120 juvenile trout and then fed each fish either a low, intermediate, or unlimited food ration in individual tanks in the laboratory. After two weeks we measured how much they had grown and examined whether the growth rates of individuals differing in their SMR and AS depended on food level. We found that an individual’s SMR was not correlated with its AS but both metabolic traits affected growth. However, their effects depended on each other and also on food level. Growth was faster at higher food levels, but individuals with different SMR and AS performed differently at each food level such that there was no combination of SMR and AS that was associated with the fastest or slowest growth at all food levels. These results demonstrate the importance of AS in explaining growth rates and provide evidence that links between individual variation in metabolism and fitness can depend on environmental conditions, in this case food level.

Image caption: Photo of brown trout. Copyright Sonya Auer.
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.

 

A cross-seasonal perspective on local adaptation: Metabolic plasticity mediates responses to winter in a thermal-generalist moth

Caroline M. Williams, Wesley D. Chick & Brent J. SinclairImage provided by authors.

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Across latitudinal and altitudinal gradients, environmental conditions vary strongly. To cope with these changing conditions, populations of organisms may be adapted to their local conditions, allowing them to survive and thrive better in their home environment than would populations from other regions. In temperate regions, this local adaptation must serve the organisms across their whole lifecycle, but characteristics that enhance survival and performance in one season may be detrimental in other seasons. Thus, to understand local adaptation we need to look at survival and performance across seasons, but most studies to date have focused only on the summer growing season. We tested for local adaptation to winter conditions in a common species of moth, Hyphantria cunea, which occurs throughout North America in diverse thermal environments. We collected larvae from the northern edge and centre of their geographic range, exposed them to both northern and central winter conditions in the lab, and monitored their survival and performance throughout the winter and into the next spring. We found that indeed the populations were locally adapted to their winter environment, with higher rates of survival and larger size and carbohydrate reserves when overwintered at their home conditions. This suggests that climate change may disrupt populations of this moth from their optimal conditions, and that populations may suffer if winter and growing season temperatures become decoupled.

Image caption: Image 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.

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