Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

Advances and challenges in the study of ecological networks

Everything is connected: new tools for understanding and managing forests

Darren M.Evans, James J. N. Kitson, David H. Lunt, Nigel A. Straw & Michael. J. O. PocockSampling for forest insects to create ecological networks can be hazardous when invasive species with urticating hairs (such as Thaumetopoea processionea) are present (note masks and gloves are removed for the photograph). Photo: DM Evans.

Forests hold a large proportion of global biodiversity and terrestrial carbon stocks and are under significant threats and pressures globally. In the UK, forests are managed mainly for commercial and amenity uses but many are vulnerable to a growing number of diseases (such as Chalara dieback of ash Hymenoscyphus fraxineus and Dothistroma needle blight Dothistroma septosporum) and/or non-native invasive insects (such as Oak processionary moth Thaumetopoea processionea and Asian longhorn beetle Anoplophora glabripennis). There is considerable interest by ecologists and land managers to not only determine the ecological consequences of losing tree species as a result of pests and diseases, but to find new ways of making forests more resilient to environmental change. However, this requires a much better understanding of the complex ways in which trees, insects and other organisms interact within forests than is currently available.

In this Extended Spotlight, we examine how recent advances in both molecular and community ecology can be combined to create highly-resolved species-interaction networks that can better inform the management of terrestrial ecosystems. Ecological networks describe the interactions between species and provide a powerful way of examining the underlying structure of communities as well as ecosystem functioning and stability. Here, we visualize the known interactions between all British tree genera, their herbivores and their associated parasitoids and show that considerable herbivore-parasitoid data is incomplete or missing. To overcome this problem (or when creating a network from scratch) we show how new DNA sequencing technology provides enormous potential for creating bigger, better networks as well as determining hitherto difficult to observe species interactions.

By combining ‘DNA metabarcoding’ with ecological network analysis we provide a novel framework by which forests can be studied and managed. For example, species-interaction data can be used to examine the robustness of forests to tree species loss, for targeted insect pest management and even for planning more resilient forests for the future. Overall, we demonstrate how these approaches can be merged to create important new tools for understanding large-scale ecological and evolutionary processes.

Image caption: Sampling for forest insects to create ecological networks can be hazardous when invasive species with urticating hairs (such as Thaumetopoea processionea) are present (note masks and gloves are removed for the photograph). Photo: DM Evans.
You can read the article in full here.

 

Leaf functional traits are decoupled among eucalyptus genotypes under ambient and elevated CO2

Chris J. Blackman, Michael J. Aspinwall, Víctor Resco de Dios, Renee Smith and David T. Tissue Eucalptus. Photo provided by authors.

In leaves, high rates of photosynthesis are typically associated with high levels of leaf water supply and demand, high levels of leaf nitrogen and low levels of investment in leaf mass per unit area (LMA). These trait associations are thought to contribute to defining ‘fast’ vs. ‘slow’ performance strategies in plants. While the consistency of these trait relationships varies among different groups of species, the level of trait coordination among genotypes (genetically distinct individuals) of a single species remains largely unknown.

In this study we examined the level of coordination in leaf functional traits among 14 genotypes of a widespread and iconic species of eucalypt (Eucalyptus camaldulensis spp. Camaldulensis) grown in a sunlit glasshouse under well-watered and fertilised conditions. We also examined the effect of growth under variable concentrations of atmospheric CO2 in an effort to understand how rising levels of CO2 may affect patterns of leaf functional trait coordination among genotypes.

We found that leaf functional traits related to photosynthesis (e.g. net photosynthesis and photosynthetic biochemistry), leaf water transport (e.g. leaf venation and stomatal traits) and leaf economics (e.g. LMA and leaf nitrogen) were unrelated to each other among genotypes grown in ambient CO2 (aCO2). However, close associations were observed among suites of traits within each functional ‘group’. We also found that plant growth in elevated CO2 (eCO2) did not substantially alter patterns of trait coordination among genotypes, even though the level and direction of the eCO2 response varied among traits.

Our findings clearly indicate that different suites of leaf functional traits can vary independently of each other, even among genotypes of a single species. A major implication of this result is that leaf functional traits may be free to respond to changes in the environment in different ways, without being constrained by strong linkages to other traits. However, our results also suggest that eCO2 does not seem to be a very strong selective agent in altering patterns of trait coordination among genotypes.

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

 

Plants helping plants: a relationship that evolves with age

Jose A Navarro-Cano, Marta Goberna, Alfonso Valiente-Banuet and Miguel VerdúThe nurse shrub Ononis tridentata with its beneficiary plant species on a gypsum outcrop in SE Spain (photo credit: Jose A. Navarro Cano).

Plant facilitation, the mechanism by which one plant species (nurse) gives benefits to the activity or presence of other plant species (beneficiaries) has been reported in areas of high abiotic stress throughout the world. Here, we deal with the topic of plant facilitation in a gypsum ecosystem controlled by soil toxicity and water-stress, through the seldom-explored approach of the evolution of plant nursing abilities with nurse age. We assessed by a manipulative experiment and observational data whether the same nurse plant facilitates species with contrasted functional traits along its lifespan. We hypothesized that early-successional species, with lower nutritional requirements, emerge better below younger nurses whereas late-successional species, which require mature ecosystem conditions, need older nurses. Our results show that facilitation allows the establishment of both plant functional types beneath the same nurse, but in a different temporal sequence determined by nurse age, which determine a reverse stress gradient. Our research adds the time perspective to the nursing ability of some species thus enabling the assembly of both “early-” and “late-successional species” below the same nurse plant species. In light of our results we suggest a revision of the role of facilitative interactions in community assembly rules under severe abiotic stress conditions.

Image caption: The nurse shrub Ononis tridentata with its beneficiary plant species on a gypsum outcrop in SE Spain (photo credit: Jose A. Navarro Cano).
You can read the article in full here.

 

Reproductive effort alters immune parameters measured post-partum in European rabbits under semi-natural conditions

Heiko G. Rödel, Manuela Zapka, Volker Stefanski and Dietrich von HolstEuropean rabbit mother (with coloured aluminium ear tag) closing the entrance of the burrow (left) including the nest with her offspring after nursing. Photo by Heiko G. Rödel.

Reproduction is energetically costly, and mothers’ resource allocation to reproduction might compromise other physiological functions such as the immune system. These interactions between reproductive effort and immune function have been frequently explored in birds, but hardly in mammals under natural conditions.

We studied such purported negative associations between reproductive effort and immunity in female European rabbits in a field enclosure. To this end, we explored whether mothers’ reproductive effort, measured as litter mass and size and whether the females had given birth to another litter shortly before, were associated with different maternal immune parameters measured post-partum.

We found that mothers with higher reproductive effort showed lower concentrations of white blood cells, in particular of neutrophils and lymphocytes, supporting the existence of a negative association between reproduction and immunity. However, there was also evidence for a positive association between reproductive effort and immune parameters measured from serum, such as immunoglobulin G concentrations and the functionality of the complement system (proteins that enhance the ability of antibodies and phagocytes to deal with pathogens). These parameters were increased in mothers with higher litter size or mass. Interestingly, corresponding negative or positive associations with respect to the immune parameters considered were also apparent when comparing changes in immune parameters and reproductive effort on the individual level – that is, when focussing on females which repeatedly reproduced within the breeding season, and either increased or decreased their reproductive effort during consecutive reproductive events.

In conclusion, the findings of our study underline differential responses of different branches of the maternal post-partum immune system to variation in mothers’ reproductive effort. On the one hand, our females might compromise at least some cellular immune parameters for reproduction. On the other hand, we hypothesize that positive associations such as between immunoglobulin G and reproductive effort could be favoured by evolution, as a higher number of pups requires an intensified transfer of maternal immune parameters via placenta or colostrum and milk to protect the offspring during early postnatal life.

Image caption: European rabbit mother (with coloured aluminium ear tag) closing the entrance of the burrow (left) including the nest with her offspring after nursing. Photo by Heiko G. Rödel.
You can read the article in full here.

 

Nutrient utilization traits vary systematically with intraspecific cell size plasticity

Martino E. Malerba, Kirsten Heimann, Sean R. ConnollyImage provided by authors.

Analyzing how species respond to changes in the environment is at the heart of ecology. Growth, age, nutrient uptake etc. are species traits used to measure these responses and interpret impacts of environmental conditions on the species composition of ecosystems (reefs, rainforests, etc.). However, these traits can be quite variable, even for the same species (this variation is often termed “intraspecific trait plasticity”). For instance, individuals of the same plant species can display very different traits depending on the environmental conditions they are growing in.

Small one-celled algae (phytoplankton) are known to thrive and bloom primarily due to large nutrient inputs (e.g. nitrogen) into our waterways and seas. Almost all life on earth is directly or indirectly dependent on phytoplankton primary productivity. Today we know that differences in species traits are very important to understand phytoplankton ecology. But virtually nothing is known about how variable traits are within the same phytoplankton species. For instance, we know that cells can change their volume, depending on physiological and environmental conditions. What we do not know is whether the traits of a species change together with the size of a cell.

 

In this study we considered the growth of populations of a single phytoplankton species reared under different nutrient (i.e. nitrate and ammonium) conditions. We found that cells with different nutrient histories exhibit different traits. More importantly, we also found a systematic change between the traits of a species and the mean cell size in the population. This means that environmental conditions favouring smaller or larger cells would also influence the traits of a species. Not accounting for the effects of cell size and previous nutrient history can substantially reduce our ability to understand and predict the dynamics of a species. These results highlight the importance of size plasticity in ecology and suggest that intraspecific variability might play an important role in shaping natural communities.

 

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

 

Experimentally manipulating the harmful products of respiration

Rebecca E. Koch and Geoffrey E. Hill The house finch (Haemorhous mexicanus) is one of the several species in which paraquat has been used as a physiological ROS generator within the field of oxidative stress ecology. Photo credit to co-author Geoff Hill.

Life requires that energy stored in molecules such as sugars and fats be released and converted into forms of energy that can run cellular processes. Such energy release is inherently inefficient, however, such that some energy is dissipated as heat and some energy ends up changing oxygen molecules into charged particles known as free radicals, which can damage cellular components like membranes and DNA. The amount of free radicals produced in cellular respiration varies among individuals and species, with important consequences for health and fitness—as a matter of fact, free radical damage has been implicated as a major factor in the process of aging. To study processes like free radical damage, scientists require methods to stimulate the production of free radicals or inhibit counter-acting molecules known as antioxidants. By experimentally simulating high levels of free radicals within an animal’s body, we can learn how some individuals are better able to withstand free radical damage and prevent its harmful effects. We reviewed all of the methods for manipulating free radicals that are available to scientists working with vertebrates in an ecological context. We conclude that the toxic herbicides paraquat and diquat are the most effective agents for causing more free radicals to be released by the cells of an animal. These compounds are poisons because they can induce a fatal release of free radicals in humans and other animals. However, if small and carefully regulated doses are used, then free radical release can be stimulated at a less than a lethal level. The other most effective means to increase free radicals in animal cells is to suppress the action of antioxidants. Currently, chemical suppression is possible in some animals, but new genetic techniques that can shut down targeted genes will likely soon become the best means of manipulating free radicals. With the right tools, biologists can tackle fundamental problems like the role of free radical buildup in the process of aging.

Image caption: The house finch (Haemorhous mexicanus) is one of the several species in which paraquat has been used as a physiological ROS generator within the field of oxidative stress ecology. Photo credit to co-author Geoff Hill.
You can read the article in full here.

 

Food, temperature, and endurance: Effects of food deprivation on the thermal sensitivity of physiological performance

Anthony L. Gilbert and Donald B. MilesMale Urosaurus ornatus. Image provided by authors.

Lizards are a group of terrestrial vertebrates at great risk from changes in global climate because their physiology is dependent on environmental temperature. The focus of research that attempts to estimate lizard responses to climate change has traditionally relied only on changes in temperature, while neglecting other simultaneous changes to the environment. In arid desert ecosystems, warmer temperatures will alter precipitation patterns, further reducing the scant rainfall these areas already receive. As a result, reduced primary productivity is expected to limit prey abundance for a multitude of predators. Physiology, while dependent on temperature, can also be influenced by energetic state, and this is a relationship that has not received much attention especially in lizards and with respect to rapidly changing climates. We examined whether the relationship between physiology and temperature for the tree lizard (Urosaurus ornatus) is affected by food availability. We estimated locomotor performance (endurance capacity), thermal preference, and the thermal sensitivity of locomotor performance for fasted and fed groups of U. ornatus to evaluate the effect of food deprivation on thermal physiology.

We found that food-deprived lizards exhibited reduced endurance running capacity, lowered preferred body temperatures, and a thermal sensitivity of performance favorable for cooler body temperatures compared to fed lizards. This indicates that lizards that are unable to forage effectively will restrict themselves to cooler regions of their habitat and be at a physiological disadvantage for being active at warmer periods of the day. This will further restrict foraging opportunities and intensify energetic imbalance. Our work demonstrates an energetic mechanism by which changes in climate could lead to shifts in lizard activity and ultimately demographic instability and extinction.

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

 

Trade-offs among endurance capacity, reproduction, and immunity in lizards

Jerry F. Husak, Haley A. Ferguson and Matthew B. Lovern Lizard. Image provided by authors.

Because resources are limited, investment of acquired energetic resources into a particular trait denies those same resources from being allocated to another trait, resulting in life-history trade-offs. Classic life-history traits such as reproduction and immunity clearly influence fitness and have been the primary focus of ecological research. However, performance traits such as locomotor capacity are also key to fitness and are energetically expensive, yet they are seldom integrated into life-history studies. We manipulated diet and forced allocation of resources to performance, via exercise training, to examine trade-offs among endurance capacity, growth, immune function, and investment in reproduction. Captive green anole lizards were assigned to one of four treatment combinations across two factors (diet restricted or not and endurance trained or not) over the course of nine weeks. Our results show that training enhances endurance performance, regardless of diet treatment, due to increased heart size and volume of red blood cells. Both diet restriction and training dramatically suppressed reproduction and immune function, but there were opposing effects of diet restriction and training on growth: diet restriction decreased it, but training increased it. Elevated stress hormone levels from training were associated with suppression of immunity, and decreased fat stores from diet restriction were associated with suppressed reproduction in both sexes. By forcing allocation of resources to performance with exercise training, we revealed that performance enhancement comes at a cost, suggesting that locomotor performance is an important part of energy allocation decisions and thus a key component of life-history trade-offs.

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

 

Losing reduces bite force in crickets

Catriona Condon and Simon P. LailvauxAcheta domesticus. Photo provided by authors.

In many animal species, males fight over access to females or resources that females need. Although actually coming to blows is rare because no-one involved wants to be injured, fights can escalate and become physical if they cannot be resolved through other means such as mutual display. When this happens, a male’s chances of winning a fight is often based on how strong or fast he is. Because many animals bite each other during aggressive interactions, bite force would seem to be an important determinant of a male’s ability to win a fight, and evidence suggests that this is indeed the case for a variety of animal species from lizards to insects. However, other factors can affect the chance of winning a fight, including fight experience, and studies have shown that animals that have recently lost a fight are more likely to lose subsequent fights. This suggests that fighting ability based on, for example, bite force, actually decreases in animals that lose fights. Such a decrease would be surprising because while maximum bite force can potentially be affected by factors including size, diet, and head shape, in the short term an animal’s maximum bite ability would be expected to change very little, and thus his fighting ability should remain relatively constant.

We measured bite force and staged male combat contests in the cricket Acheta domesticus to answer two questions: first, whether individual bite force affects male combat outcomes; and second, whether losing a fight affects a male’s ability to bite and therefore fight. We found that bite force does indeed influence fight outcomes in A. domesticus, with animals that bite harder relative to their opponents being more likely to win an initial male combat bout. When we made males fight a second bout shortly after, we found that animals that lost either the first or both rounds of combat indeed decreased their bite force compared to animals that won just the first round, that won both rounds, or that never fought and therefore never lost. Animals that lose fights therefore show reduced bite force.

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

 

Inbreeding and neighbouring vegetation drive drought-induced die-off within juniper populations

Francisco Lloret and Cristina García Juniper in different conditions. Image provided by authors.

Massive forest die-off events in response to increasingly frequent and prolonged droughts have been reported worldwide during recent decades. Prolonged and more intensive droughts are expected to hit Mediterranean ecosystems hard, and these effects are already reported to be aggravated by anthropogenic warming. To date, we have a reasonably good understanding of the ecological (plant-plant interactions) and physiological mechanisms (reduced levels of evapotranspiration) that underlie forest responses to drought, yet the role of population genetic diversity remains unclear.

The genetic population literature has already documented the deleterious effects of increased inbreeding levels in both plants and animals, where high levels of inbreeding tend to correlate with declining population trends. Increased inbreeding usually arises as a consequence of frequent mating among relatives, for example due to small population sizes in deforested landscapes, and they typically entail a poor performance of highly inbred individuals compared to less inbred ones. Therefore, we would expect that individual inbreeding would influence the ability of individuals to cope with an extreme climate event, such a prolonged drought.

Specifically, we tested whether the level of individual inbreeding played a role in the response of Mediterranean juniper trees (Juniperus phoenicea) inhabiting a semi-arid ecosystem after a prolonged drought event. As expected the level of individual inbreeding negatively affected both vegetative and reproductive responses to drought, and less inbred individuals were more likely to remain unaffected than highly inbred ones. Additionally we found that neighboring vegetation alleviated the negative effects of drought, with trees growing in open sites showing increased levels of canopy damage. These results reveal the need to integrate ecological and genetic factors when studying forest responses to climate extremes.

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

Perspective

Are leaves more vulnerable to cavitation than branches?

Shi-Dan Zhu, Hui Liu, Qiu-Yuan Xu, Kun-Fang Cao and Qing Ye The tropical wet forest in southwestern China (photo was taken by Shi-Dan Zhu).

Cavitation, blockage of a plant’s water conducting cells (xylem) by air, can be initiated by the entry of air through conduit pit membranes, causing embolized (air-blocked) conduits, when tension in the xylem increases during water stress. Cavitation is of importance to plants because it reduces hydraulic conductivity, which in turn impairs photosynthesis and growth. A number of studies have examined the vulnerability to drought-induced cavitation in both leaves and branches of woody plants, and a general finding is that branches are more resistant to cavitation than their terminal leaves. This is consistent with the hydraulic vulnerability segmentation hypothesis, which proposes that leaves are preferentially sacrificed to protect the hydraulic safety of branches. However, several studies have shown that leaves can be less vulnerable to cavitation than branches, indicating a Lack of Vulnerability Segmentation in these species (i.e., LVS species). Therefore, it is intriguing to evaluate how general vulnerability segmentation is in species from habitats with different climatic conditions.

Here we compiled branch and leaf hydraulic trait data for 69 broadleaved woody species from four different biomes (i.e., tropical rain forest; tropical seasonal forest; temperate seasonal forest; and Mediterranean shrub/woodland). The results showed that vulnerability segmentation was common for species from arid regions, with exceptions for some LVS species from humid regions displaying more hydraulically vulnerable branches than their leaves. Although leaves of LVS species might lose their function as “safety valves” to protect branches from hydraulic failure, they may adopt certain compensatory hydraulic strategies (e.g., wider leaf hydraulic safety margins, better water status, and greater xylem hydraulic conductivity) to achieve water balance. Therefore, with robust cavitation-resistant leaves and effective hydraulic compensatory strategies, LVS species could maintain water supply and functionality of leaves, thus giving them a competitive advantage in the face of potential drought events, such as the strong rainfall seasonality in humid regions.

Image caption: The tropical wet forest in southwestern China (photo was taken by Shi-Dan Zhu).
You can read the article in full here.

 

Land use change in the Amazon rainforest favors generalist fungi

Rebecca C Mueller, Jorge LM Rodrigues, Klaus Nüsslein and Brendan JM BohannanImage provided by authors.

Land use change, such as conversion of native forests to agriculture, has been shown to have significant negative impacts on the biodiversity of plants and animals. Many studies have also documented the loss of specialist species and the proliferation of generalist, or “weedy” species; however, whether land use change has similar effects on microbial communities is still unclear. Because soil microbial communities are responsible for a wide range of ecosystem functions, such as nutrient cycling, understanding their responses could provide insights into the long-term effects of large-scale deforestation.

Using long-term plots established within multiple land use types in the Amazon rainforest, we quantified the response of soil fungal communities to land use change. We sampled pastures created by the deforestation of primary forest, and secondary forests generated by natural re-colonization of abandoned pastures by forest plants. We measured fungal richness and composition and identified factors associated with shifts in community composition across multiple land use types. In addition, we used distribution patterns of fungi to determine if widely distributed, generalist species were favored by land use change.

Fungal richness was significantly lower in pasture soils compared to primary forests, and the composition of the fungal community differed significantly between primary forest and pastures. Distance to primary forests was the strongest correlate of community composition in pastures, indicating that primary forests can act as reservoirs for re-colonization by native fungi. Generalist fungi were strongly favored in all pasture sites, regardless of time since conversion. The two secondary forests showed variable patterns of richness, composition, and the overall abundance of generalist fungi, suggesting that community recovery is unpredictable.

Similar to patterns documented in plants and animals, we found that fungal richness declined in pastures, with significant shifts in community composition and an associated increase in generalist species. Together, these findings suggest that the increased prevalence of generalists is a consistent response to disturbance across broad taxonomic groups.

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

 

The carbon to phosphorus critical ratio of soil microbial community demand

Petr Čapek, Petr Kotas, Stefano Manzoni and Hana ŠantrůčkovaImage provided by authors.

Nutrient limitation of soil microbial communities is considered to play an important role in ecosystem functioning. The soil microbial community controls the decomposition of dead plant material and therefore its nutrient limitation is commonly included in mathematical models of ecosystem functioning. However, it is not always easy to recognize nutrient limitation. Therefore, guidelines to recognize nutrient limitation were defined. These guidelines are based on ecological stoichiometry theory. According to this theory, there exists a critical carbon (C) to nutrient (E) ratio of substrate that the microbial community feeds on. Above the critical ratio (C:ECR), nutrients are considered to be in insufficient amount and thus limiting. The C to phosphorus (P) critical ratio (C:PCR) that determines P limitation of the soil microbial community is largely unknown and thus it is the subject of our experimental study. Our results show that C:PCR may be extremely variable. Some soil microbial communities can have C:PCR below 30, whereas others can have C:PCR above 400. The C:PCR cannot be simply predicted for microbial communities. There are very likely many factors that affect soil microbial communities C:PCR. More studies would be needed to disentangle the controls over C:PCR. However, one unexpected result of our study is that soil microbial communities are able to store P compounds inside their cells that allow them to temporarily grow without presence of P in soil. This may represent a widely adopted strategy of soil microorganisms.

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

 

Effects of single and mixed infections of bean pod mottle virus and soybean mosaic virus on hosts and vectors

Maria Fernanda G. V. Peñaflor, Kerry E. Mauck, Kelly J. Alves, Consuelo M. De Moraes and Mark C. Mescher Arthropod vectors of viruses that infect soybean plants. Left: larval (above) and adult stages of the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera:Coccinellidae), which transmits Bean pod mottle virus (BPMV).  Right: the soybean aphid,Aphis glycines Matsumura (Hemiptera: Aphididae), which transmits Soybean mosaicvirus (SMV). Images by Hannier Pulido (Epilachna varivestis) and Kerry Mauck (Aphis glycines).

Plant-infecting viruses have significant impacts on human agriculture and also play important roles in the ecology of natural plant populations. Most plant viruses are transmitted by arthropod vectors, especially insects, and their spread thus depends on the nature and frequency of interactions among plants and vectors. Recent work has shown that such interactions can be influenced by virus-induced changes in ecologically relevant plant traits, such as plant nutritional and defense chemistry or plant-derived visual and olfactory cues that influence the foraging and feeding behavior of herbivorous arthropods. In many cases, the effects of viruses on such traits, and the associated changes in patterns of plant-vector interactions, appear conducive to virus transmission.

However, little is known about the ecological implications of co-infection of the same host plant by two or more viruses, even though multiple infections are common in both natural and agricultural ecosystems. To explore this issue, we documented the effects of single and mixed infection of soybean plants by bean pod mottle virus (BPMV) and soybean mosaic virus (SMV) on key biochemical plant traits and on the behaviour and performance of a beetle vector of BPMV (Epilachna varivestis) and an aphid vector of SMV (Aphis glycines). Our primary goals were to understand how virus-induced changes in plant phenotypes might influence (i) the acquisition and transmission of each virus by its respective vector in single infections, (ii) the likelihood of secondary infection for plants singly infected with either virus, and (iii) the implications of co-infection for virus transmission by vectors. We documented significant effects of each virus on ecologically relevant host-plant traits and on the preferences and performance of its respective vector (as well as effects of SMV on plant palatability for the BPMV vector E. varivestis). However, most of these effects were not observed in plants with co-infections. These results suggest that co-infection can, in at least some cases, attenuate the effects of individual viruses on plant-vector interactions and, to the extent that such effects are adaptive for the virus, may thereby reduce disease transmission.

Image caption: Arthropod vectors of viruses that infect soybean plants. Left: larval (above) and adult stages of the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera:Coccinellidae), which transmits Bean pod mottle virus (BPMV). Right: the soybean aphid,Aphis glycines Matsumura (Hemiptera: Aphididae), which transmits Soybean mosaicvirus (SMV). Images by Hannier Pulido (Epilachna varivestis) and Kerry Mauck (Aphis glycines).
You can read the article in full here.

 

Group foraging decisions in nutritionally differentiated environments

Matthew J Hansen, Timothy M Schaerf, Stephen J Simpson and Ashley J W WardImage provided by authors.

Food in the environment is temporally and spatially variable and much work in behavioural ecology looks at how animals adjust their foraging behaviour in order to adapt to this variation. However, food also varies in its macro-nutrient composition and studies of foraging behaviour will be more accurate if they acknowledge the extent to which animals can detect and regulate their intake of food based on these differences in food composition. Whilst theory is developing around this subject, only very recently has this theory been extended to group foraging behaviour, and there have been few empirical studies on how the distribution of macro-nutrients in the environment affects vertebrate foraging behaviour. Therefore, we monitored the movements of 8 mosquitofish as they foraged in two environments that contain equal amounts of available energy but differ in their distribution of macro-nutrients. We show that fish will distribute themselves within an environment in relation to the distribution of specific macro-nutrients. Also, fish make foraging decisions based on the macronutrient composition of patches, such that they stay longer in patches with a higher concentration of protein and lower concentration of carbohydrate. This study confirms the importance of considering the macro-nutrient composition of foods when considering the movement decisions of foraging groups, and thus has important consequences for developing more accurate foraging models that take into account the distribution of macro-nutrients in the environment. The results suggest the spatial distribution of nutrients on a landscape scale could influence grouping patterns and social interactions, thus affecting population dynamics.

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

 

Nutrient inputs affect foodwebs in estuaries

Fiona Y. Warry, Paul Reich, Perran L. M. Cook, Ralph Mac Nally , James R. Thomson, Ryan J. Woodland The mouth of Wingan Inlet, Victoria, Australia; an estuary receiving relatively low inorganic nitrogen loads. Source: F. Y. Warry.

Excess nitrogen and phosphorus from river catchments can be transported to estuaries where they can alter how these ecosystems function. The effects of elevated nutrients can include altered plant assemblage composition, plant growth and water quality which will have flow on effects for consumers such as fish. However, the effects of nutrient levels entering an estuary will be modulated by the degree of tidal exchange and freshwater flow.

We used stable isotopes of nitrogen and carbon to investigate the effect of nutrient loading on estuarine fish assemblages. The stable isotope composition of fish muscle tissue can be used to indicate its diet and therefore determine how foodwebs, or parts of foodwebs, are arranged. We used metrics derived from carbon and nitrogen stable isotope values of fish and plant tissue collected from nine estuaries to assess how foodwebs were influenced by nitrogen and phosphorous inputs.

The part of the estuarine foodweb occupied by fish became more diverse with increasing inorganic nitrogen inputs. This means fish were utilizing a larger range of nutrition sources, relative to those that were available to them. Total nitrogen and total phosphorous levels had little influence on foodweb arrangement.

The nitrogen loads received by some of our estuaries were high by global standards and were within ranges where seagrass commonly dies because it is overgrown by macroalgae (‘seaweeds’). Macroalgae can take up nutrients more quickly than seagrass so can thrive under high nutrient conditions. However, seagrass remained in all our estuaries possibly due to short water residence times. Other research in our estuaries has shown that overall there is more vegetation when inorganic nitrogen levels increase. Therefore, fish may be able to feed on a more diverse range of prey because greater amounts of vegetation may increase the productivity of small invertebrate prey, and/or fish have more shelter from predation so can be more adventurous in their feeding. The nutrient content of plants may also increase in estuaries with higher inorganic nitrogen levels, increasing their palatability to grazers with flow on effects to fish. Our results demonstrate the crucial role of nitrogen for estuarine foodweb function.

 

Image caption: The mouth of Wingan Inlet, Victoria, Australia; an estuary receiving relatively low inorganic nitrogen loads. Source: F. Y. Warry.
You can read the article in full here.

Review

Drivers of individual differences in the ability to transmit pathogens

Kimberly L. VanderWaal and Vanessa O. EzenwaIndividual variation in pathogen transmission potential has been examined by the authors for several savanna wildlife species, including giraffe, in central Kenya. Photo credit: Kimberly VanderWaal.

In many outbreaks of infectious diseases, a relatively small number of individuals are responsible for the majority of new cases. One of the most famous examples is ‘Typhoid Mary’, who was responsible for 28 outbreaks of typhoid fever in the early 20th century, but there is evidence for “super-spreaders” in many other human and animal disease outbreaks, including HIV, Ebola, brucellosis and West Nile Virus. A general rule-of-thumb is that 20% of infected individuals are responsible for infecting 80% of new cases. Because this phenomenon has key implications for predicting and controlling the spread of infectious diseases, understanding the underlying mechanisms that drive individual variation in pathogen transmission potential has emerged as an important research frontier in both epidemiology and disease ecology.

In this review, we explore the impact of behavior and physiology on variation in the number of new infections produced by an individual, which we define as V. V can be affected by behavioral differences among individuals, such as gregariousness or other personality traits, and by physiological differences, including differences in immune factors, nutrition, and sex. In general, these mechanisms interact with three components that determine V: contact rates between individuals, likelihood of transmission given contact, and the length of time an individual remains infectious. Here, we synthesize scientific literature from multiple fields, and show that behavioral and physiological mechanisms have typically been examined in isolation, yielding an incomplete picture of the drivers of individual differences in transmission potential. Our review emphasizes the need for a more holistic approach for analyzing V. We also describe new tools and methods for assembling the disparate processes that contribute to individual variation in transmission potential in order to gain an improved understanding of the spread of infectious diseases in natural populations.

Image caption: Individual variation in pathogen transmission potential has been examined by the authors for several savanna wildlife species, including giraffe, in central Kenya. Photo credit: Kimberly VanderWaal.
You can read the article in full here.

 

A time to kill: What determines when wolves kill moose?

Lucas M. Vander Vennen, Brent R. Patterson, Arthur R. Rodgers, Scott Moffatt, Morgan L. Anderson and John M. FryxellA wolf in northern Ontario (photo credit: Lucas M. Vander Vennen).

The opposing goals of predators and prey can lead to dynamic behavioural interactions, wherein predators attempt to increase predation success and prey try to decrease predation risk. These interactions give rise to many of the predator-prey behaviours we see today, but our understanding of these patterns is often limited by knowledge of what influences predator success and prey risk. Here we look at predator and prey interactions between wolves and moose over the course of the 24-hour daily cycle. We use data from GPS collars to investigate what factors drive the rates at which wolves kill moose. We found wolf-killed moose using wolf collar data, and examine how the temporal pattern of these kills is related to wolf movement, moose movement, and ambient light conditions throughout the period of the 24-hour cycle. We found that kill rate is very well explained by the combined movement speeds of wolves and moose, such that higher movement rates correspond to higher kill rates. This relationship has often been applied to these types of interactions, but our work represents the first field-based test. Interestingly, this effect of movement speed is almost entirely driven by wolves, with very little input from moose. Wolves moved over ten times faster than moose, and so had a much greater influence on their overall combined velocity. Kill rates were not influenced by light conditions, but instead were almost entirely driven by wolf movement rates. While moose may have influence on predation through behavioural adjustments (e.g. vigilance or selecting habitats that provide protection during risky times of day), this indicates that the prey in this system are not able to adjust their predation risk by being active at different times of the day.

Image caption: A wolf in northern Ontario (photo credit: Lucas M. Vander Vennen).
You can read the article in full here.

 

Using nutritional geometry to study the effects of parental diet on offspring

Russell Bonduriansky, Aidan Runagall-McNaull, Angela J. CreanNeriid flies feeding on damaged tree bark in Sydney, Australia.

You’ve probably heard that you are what you eat, and may even have heard that you are what your parents ate. But the truth is that we still know very little about how an individual’s diet affects the viability, health and features of its offspring.

Part of the problem is that past studies have compared the effects of just two or three kinds of food. They have also tended to focus on the effects of mother’s diet, typically ignoring the father altogether.

But we all know that diets are complex and variable, and their effects can be decidedly nonlinear: two sausage rolls a month might make no noticeable difference to your health, but ten sausage rolls a month might do serious damage. Moreover, recent studies have shown that what fathers eat (for example, how much fat they consume) can indeed affect their offspring, but very few attempts have been made to compare the effects of nutrients in maternal and paternal diets.

We tackled these gaps in knowledge using an approach called “nutritional geometry,” which involves raising experimental subjects on many different diets consisting of different nutrient ratios and concentrations. Nutritional geometry has been used in many previous studies to determine how individuals are affected by their own diet, but we used this approach for the first time to investigate how parental diet affects offspring, and we did this for both maternal and paternal diets. For this experiment, we used a beautiful Australian neriid fly that has served for several years as our “guinea pig” in research on the effects of diet within and across generations.

All this work paid off: We found that macronutrients (protein and carbohydrate) in maternal and paternal diets can have very different (indeed, sometimes opposite) effects on offspring. We were also able to show that the effects of parental diets can be highly non-linear, and that different dietary nutrients can interact in their effects on offspring. We hope that our work will inspire other researchers to use nutritional geometry in studies on the effects of parental diet.

Image caption: Neriid flies feeding on damaged tree bark in Sydney, Australia.
You can read the article in full here.

 

Socioecological predictors of immunity in wild spotted hyenas

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

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

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

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

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

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

 

Ecological equivalence of species within phytoplankton functional groups

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

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

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

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

 

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

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

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

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

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

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

 

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

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

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

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

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

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

Image caption: Image provided by authors.
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Genes that influence salmon growth in wild don’t matter in captivity

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

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

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

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

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

 

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

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

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

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

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

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

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

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

 

Both spreading and non-spreading exotic plants receive sufficient pollination

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

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

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

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

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

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

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

 

Wildlife mobility and extinction risk in human-altered landscapes

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

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

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

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

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

 

Parental age influences offspring telomere loss

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

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

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

 

Ecological relevance of cellular energy metabolism in intertidal species

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

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

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

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

Image caption: After a summer thundershower, a limpet, Cellana toreuma, habitat on a rocky shore in Dongshan, Fujian, PR. China.
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Top-down becomes bottom-up: consequences of nutrient cycling for trophic cascades between green and brown webs

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

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

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

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

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

 

Reseeders benefit from arid climates and infertile soils

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

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

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

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

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

Image caption: Restioid fynbos at the Roikloof dam near Ceres, South Africa. Photograph: R. O. Wüest.
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How do soil respiration components and their specific respiration change with forest succession?

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

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

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

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

 

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

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

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

Image caption: A mixed forest in the French Pyrenees on May 1 2007. Beech trees already started to sprout, when temperatures suddenly dropped and it began to snow, while less freezing resistant tree species have their leaves still in the protection of the buds. Photo credit: Y. Vitasse.
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Survival benefits of winter dormancy: warmer climates are associated with shorter hibernation seasons and reduced survival in rodents

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

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

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

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

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

Image caption: Common dormouse (Muscardinus avellanarius). Image provided by authors.
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Which is more important: direct environmental effects, or local adaptation, in determining how many times animals reproduce?

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

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

Image caption: Image provided by authors.
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Functional strategy composition is a good indicator of species dynamics

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

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

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

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

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

Image caption: The Szűcs-Holt-Tisza oxbow sampling site in summer.
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Individual decision-making by prey may affect the strength of food chains

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

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

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

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

Image caption: Leptasterias and Tegula. Photo provided by authors.
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When does clumping help insects escape parasitism?

Richard M. Gunton and Juha PöyryNatural History Museum.

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

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

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

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

Image caption: Natural History Museum.
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Do invaders most strongly impact similar species?

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

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

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

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

Image caption: Image provided by authors.
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The functional role of silicon in plant biology

Silicon in aquatic vegetation

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

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

Image caption: Researchers from Antwerp, Lund and Maun on their 2012 expedition to study the silicon cycle in the Okavango Delta, the largest inland delta in the World. Courtesy of D.J. Conley.
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City slickers: poor performance does not deter Anolis lizards from using artificial substrates in human-modified habitats

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

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

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

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

Image caption: A male Anolis cristatellus feeding while perched at the top of a brick wall. Photo by Jason J. Kolbe.
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Coexistence resulting from being more different or more similar?

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

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

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

Image caption: Bacterial colonies growing on nutrient agar plates. Competing strains are distinguishable by their colony colors. Picture by Lin Zhao.
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Evolution in space: metapopulation structure and life history evolution

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

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

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

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

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

Image caption: Spider mites as a model for experimental evolution (mature female, on bean). Photo credit by Gilles San Martin.
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Soil microbial communities matter for carbon cycling during drought

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

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

Image caption: Different land uses in the Wairau Valley, taken by Robbie Holdaway.
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Diet determines movement rates and size of area used for herbivores

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

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

Image caption: Photo provided by authors.
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Special Feature: The functional role of silicon in plant biology

Molecular evolution of aquaporins and silicon influx in plants

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

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

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

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

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

Special Feature: The functional role of silicon in plant biology

The Importance of Agriculture in Global Biogenic Silicon Production

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

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

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

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

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

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

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