Lay Summaries Archive

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Early View Lay Summaries

 

Long-lasting effects from previous winter warming events suggest that an important sub-Arctic moss will be disadvantaged in a future sub-Arctic climate

Jarle W. Bjerke, Stef Bokhorst, Terry V. Callaghan & Gareth K. PhoenixA shoot of splendid feathermoss with fertile organs (sporophytes) protruding from the green shoot segments, which are partly blurred. Photo credit: Jarle W. Bjerke.

Understanding the impacts of climate change on ecosystems is complex for many reasons. Firstly, there are many drivers of change and each driver has numerous interacting facets. Secondly, there are practical issues that hinder research, such as difficult species groups and winter research. Here we focus on a moss (an understudied plant group), the winter period (under-represented in field studies) and extreme warming events, that are both difficult to observe and even more difficult to predict. Winter is a period of dormancy for plants of cold environments. However, winter climate is changing, leading to an increasing frequency of warm weather events that temporarily reduce snow cover. These conditions can break dormancy for some plants and expose them to freeze-and-thaw stress. Mosses are a major component of northern lands, yet the longer-term impacts of such winter warming events on mosses remain unknown. Therefore, we undertook a field experiment to simulate these events over three consecutive winters in a sub-Arctic open woodland. The mat-forming splendid feathermoss (Hylocomium splendens), also known as the glittering woodmoss or stairstep moss, was the most abundant moss species at our site, and we studied it during both the experimental years and in the years following these events. This is probably one of the most abundant moss species in the World, and plays important roles such as insulating the ground. We found that the warming events reduced its vitality. Both photosynthesis and shoot growth rates declined considerably and were still much lower than in non-experimental plots even four years after the last warming event. These results suggest that this moss will be disadvantaged in a future sub-Arctic climate where a high frequency of winter warming events may become the norm. More broadly, this suggests the potential for large consequences for northern lands where mosses are often a major component of the vegetation and where the greatest increases in extreme winter events may be expected. This will again have a strong influence on ground temperature and moisture, cycling of nutrients and water, permafrost thaw and ecosystem carbon balance.

Image caption: A shoot of splendid feathermoss with fertile organs (sporophytes) protruding from the green shoot segments, which are partly blurred. Photo credit: Jarle W. Bjerke.
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Joint effects of climate change and parasite infection on host in the wild

Matthieu Bruneaux, Marko Visse, Riho Gross, Lilian Pukk, Lauri Saks, Anti VasemägiEcologist at work. Photograph provided by authors.

Climate change can affect ecosystems in several ways, through direct temperature effects on organisms (e.g. limiting metabolic capacity at high temperatures) or through indirect effects, such as an increased parasite burden or the introduction of new parasites. These negative effects can interact with potentially dramatic consequences, when high temperatures disrupt the immune function of the host and make it unable to resist a parasite infection, or when the parasite infection compromises the ability of the host to cope with elevated temperatures.

The physiological effects of parasites have been traditionally evaluated under controlled laboratory conditions. However, much less is known about the effect of emerging parasitic diseases on host performance in nature. We studied wild-caught juveniles of brown trout (Salmo trutta) and measured several physiological and performance traits to evaluate the effect of proliferative kidney disease (PKD), which is caused by the myxozoan parasite Tetracapsuloides bryosalmonae This parasite can result in high mortalities in salmonid species, both in farms and in natural ecosystems, and its range has extended in recent years. To understand how parasite load, metabolic rate and thermal resistance are related to each other in the fish host, we brought our physiological laboratory into the field to measure oxygen consumption and thermal tolerance of wild brown trout.

We found that fish exhibited varying degrees of disease severity, with a wide range of parasite load, kidney swelling and associated anemia. Importantly, the aerobic scope, which is the maximum amount of usable energy a fish can produce using its aerobic metabolism, was negatively correlated with the severity of PKD. In addition, the thermal tolerance of the fish was also negatively correlated with disease symptoms. Our results demonstrate how a wild fish population can be at risk under the double threat of increased water temperature and expanding parasite range, and of their interaction. Understanding if and how local populations can adapt to these selective pressures will be critical to assess the long term evolution of this type of ecosystem.

Image caption: Ecologist at work. Photograph provided by authors.
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The effect of egg size on hatch time and metabolic rate: theoretical and empirical insights on developing insect embryos

James L. Maino, Elia I. Pirtle, and Michael R. KearneyGumleaf Grasshopper from Australia’s Dry Eucalypt Forest. This grasshopper resembles a dry gum leaf and lays its eggs in the leaf litter. Photograph by James Maino.

As organisms change in size, they much also change in design to compensate for the mismatched scaling between surface-area and volume-based processes. Body size scaling relationships, combined with metabolic theory, allow biologists to study ecological phenomena in terms of processes at the organism level. By properly understanding biological processes at one level, higher level processes are able to be predicted and, in doing so, a mechanistic understanding is achieved. In this study we present a model based on simple energy and mass transfer processes during egg development that is able to explain how hatch time varies with species size and the time course of metabolic rate from egg lay to hatch. Our findings suggests that previous models made unrealistic assumptions regarding the metabolic activity of a freshly laid egg, leading to unreliable predictions. Metabolic theory is increasingly being applied in biology to understand a range of biological phenomena. Contributing to its success is its emphasis on the currencies of mass and energy, which are relevant at all scales of biology from the molecular to the ecosystem. Our presented model and supporting data on 98 species of insects advances our mechanistic understanding of egg development and highlights the usefulness of process-based models from which higher levels patterns can be derived.

Image caption: Gumleaf Grasshopper from Australia’s Dry Eucalypt Forest. This grasshopper resembles a dry gum leaf and lays its eggs in the leaf litter. Photograph by James Maino.
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Positive species diversity and above-ground biomass relationships are ubiquitous across forest strata despite interference from overstorey trees

Yu Zhang, Han Y.H. Chen, Anthony R. TaylorOld growth red spruce (Picea rubens) stand, typical of eastern Canadian temperate forest.  Photo Credit: Anthony Taylor.

There is growing concern over rates of global species diversity loss, given its important role in the healthy functioning of ecosystems and the many goods and services they provide. However, our knowledge of how diversity supports ecosystem function remains unclear. While positive relationships between tree species diversity and forest biomass production have been observed, forests are structurally complex, consisting of various understorey vegetation layers which also contribute to ecosystem functioning as they often account for the majority of species richness; however, the relationships between understorey vegetation diversity and function are largely unexplored. Further, few studies have simultaneously assessed how both overstorey and understorey vegetation interact and contribute to overall forest ecosystem function.

In our study, we used Canada’s National Forest Inventory data, covering many forest types across a wide spatial distribution, and a robust statistical modeling approach (structural equation modelling) to explore both overstorey and understorey relationships between species richness and forest biomass production while accounting for potentially confounding factors, including climate, physical site characteristics, and forest ageing. We found positive relationships between species richness and biomass production across all forest vegetation layers, but the relationship was strongest for the overstorey layer. Species richness of the understorey tree, shrub, and herb layers was positively related to overstorey species richness. However, overstorey biomass had a negative effect on the biomass production of all understorey layers. Our results suggest that resource filtering by overstorey trees might have reduced the strength of the positive diversity-productivity relationships in the forest understorey, supporting previous hypotheses that the magnitude and direction of diversity-productivity relationships is context specific and dependent on the conditions of the surrounding environment. Further, heterogeneity in understorey resources, as affected by overstorey trees, may promote niche complementarity (i.e. plants using different resources, or at different times or in different places) as the main mechanism driving diversity-productivity relationships in understorey vegetation.

Image caption: Old growth red spruce (Picea rubens) stand, typical of eastern Canadian temperate forest. Photo Credit: Anthony Taylor.
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Do thermoregulatory costs limit altitude distributions of Andean forest birds?

Gustavo A. Londoño, Mark A. Chappell, Jill E. Jankowski and Scott K. Robinson Andean cock-of-the-rock. Image provided by authors.

Tropical mountains contain the highest regional bird diversity in the world, largely because of high turnover of species with narrow altitudinal ranges. Understanding the mechanisms that limit so many species to narrow altitudinal distributions in the Andes is the central goal of our study. Our research is the first experimental approach to understanding the role of thermal physiology in limiting species’ altitudinal distributions. The biologist Daniel Janzen in 1967 hypothesized that tropical organisms should be specialized to a narrow range of temperatures because they experience little climatic variation in their ranges. As a result, they should be intolerant of temperatures outside of the optimal range, which would inhibit up- or downslope movements. Some tropical ectotherms (cold-blooded animals) fit Janzen’s predictions, but we do not know if endotherms, which maintain a constant internal temperature, are also excluded from environments outside their optimal temperature range. We measured several aspects of thermal physiology of 215 bird species across a 2.6-km altitude gradient in the Peruvian Andes. We predicted that highland species would show adaptation to the colder high-altitude climate, and that energy costs of thermoregulation might limit up-slope dispersal of lowland natives.

We found reductions in thermal conductance (amount of heat loss) and body temperature, and lower critical temperature (lowest temperature where metabolism increases) in highland birds compared to lowland species, all of which make birds of high elevations more resistant to heat loss. We did not, however, find convincing evidence that acute thermal limits or energy costs of thermoregulation constrained altitudinal distributions. However, to evaluate the amount of energy that low elevation birds would spend at high elevation, we built heat budget models that predicted low-to-moderate long-term costs at native altitudes. Costs increased for lowland natives modeled in the highland climate, but for all but a few species, these higher costs remained within putative expenditure limits as defined in the literature.

Although we did not test heat tolerances, we measured all species at temperatures similar to the hottest air temperatures at the lowland site. The lack of difference in basal metabolic rate at 30-34ºCdoes not suggest that high lowland temperatures preclude down-slope movements of highland birds. While thermal tolerances probably do not directly determine altitude occupancy by most species, there may be a tradeoff between the higher costs of thermoregulation experienced by lowland species moving up-slope and investment in important life history components such as breeding.

Image caption: Andean cock-of-the-rock. Image provided by authors.
Read the article in full here.

 

The plant you choose to make your home isn't always the one that protects you best

Jared G. Ali & Anurag A. Agrawal Image provided by authors.

A herbivore’s ability to feed, avoid predation, and succeed on specific host plants are some of the most important factors in its life. What we find, though, is that not all herbivores are able to perform equally well on every plant they encounter. Therefore, we assume most herbivores have specialized on plants that allow them to achieve optimal measures of performance. An important question that remains in ecology is whether herbivores select hosts more because of interactions with their host alone (nutrition, plant defenses, growth, etc.) or if predators and parasites play a major role in the selection of a plant host. A very interesting phenomenon occurs in many herbivores that specialize on particular hosts; they often gain the ability not only to cope with plant defenses (toxins produced to ward off herbivores), but to also steal them and keep them in their bodies to protect themselves from their own enemies. In this experiment we tested two specialized insect herbivores’ ability to perform on alternative plant hosts. We evaluated their performance while measuring toxins that these specialist herbivores steal from plants that might protect them from parasitic worms. We find specialization is driven primarily by plant-herbivore interactions, rather than by threat of predation/ parasitization, and that not all measures of performance are highest on the herbivores’ preferred host plants. This tells us that measures of performance are complex and that ecological interactions between a plant and host are not always those that result in optimal performance on every trait.

 

Image caption: Image provided by authors.
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Movement correlates of lizards' dorsal pigmentation patterns

Topaz Halperin, Liran Carmel and Dror HawlenaPhoto provided by authors.

The reasons why some animals have cryptic body patterns, such as spots, reticulations and blotches, while others have conspicuous stripes, has long intrigued scientists. We provide a simple explanation for this quandary that is based on the balance between the animal’s need to eat and the need to avoid being eaten. Species that remain still during much of their activity time, such as animals that hunt from ambush, may benefit from cryptic body patterns that help them blend in to the environment. However, cryptic patterns are less beneficial for species that actively search for food. This is because visual predators can easily detect a moving prey regardless of their coloration. Conversely, these highly detectable active species may benefit from conspicuous stripes that improve their chances to survive predator attacks. Stripes can dazzle the predator’s motion perception and hamper its ability to intercept escaping prey. Thus, we suggest that species that forage less actively should have cryptic patterns while species that actively search for food should have stripes. We tested this hypothesis by studying the association between lizard foraging behaviors and their pigmentation patterns. Using an extensive literature survey, we found that lizards with stripes were indeed substantially more active than lizards with cryptic patterns. Our findings provide the first quantitative support for the hypothesized relationships between pigmentation-patterns and foraging behavior. These findings might be relevant to other animals besides lizards. We hope that future studies will test our movement-patterns hypothesis, ultimately applying meticulous manipulations to tease apart and test its mechanistic details.

Image caption: Photo provided by authors.
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Testosterone and the cloacal microbiome in a free-living bird

Camilo Escallón, Matthew H. Becker, Jenifer B. Walke, Roderick V. Jensen, Guy Cormier, Lisa K. Belden, Ignacio T. Moore Image provided by authors.

Testosterone is a hormone that primarily functions to regulate reproduction in male vertebrates. It mediates processes such as sperm production, development of sexually-selected traits, and reproductive behaviors. There are many benefits for males maintaining high testosterone levels. However, it has been argued that maintaining high testosterone levels for prolonged periods also has costs, and could ultimately have negative consequences for long-term survival. One of the proposed pathways by which testosterone can affect survival is by increasing the risk of infection, including pathogenic bacteria.

We investigated testosterone and cloacal bacteria in free-living rufous-collared sparrows in the Ecuadorian Andes. Males of this species have high levels of testosterone during the breeding season, when they form socially monogamous unions with females. However, extra-pair paternity is common. We measured circulating testosterone concentrations, and assessed the diversity and types of bacteria living in their cloaca, which in birds functions as the opening from the gastrointestinal tract and is also the copulatory organ. Thus, it harbors bacteria that can be sexually transmitted.

We found that birds with higher levels of testosterone also had higher cloacal bacterial diversity, and had higher relative abundance of Chlamydiae, a group of bacteria that can be pathogenic. In addition, the cloacal microbes of low-testosterone birds were different from the rest of the males, seemingly because they were missing some bacteria that the other birds possessed. Two nonexclusive explanations for these results are that testosterone affects behaviors that lead to increased sexual contacts, and thus increased exposure to bacteria, or that testosterone is altering the bird’s immune system, thus making it easier for bacteria to colonize. Either way, these results suggests that increased exposure to sexually-transmitted pathogens in the form of cloacal bacteria could be a cost of maintaining high testosterone levels.

Image caption: Image provided by authors.
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Host phenology and potential saprotrophism of ectomycorrhizal fungi in the boreal forest

Stefan F. Hupperts, Justine Karst, Karin Pritsch, Simon LandhäusserMature aspen trees during late summer, when leaves are fully expanded and photosynthesizing at full capacity. Carbon allocation to ectomycorrhizal fungi is likely high during this phenological stage. Photo credit: Erin Wiley.

Ectomycorrhizal plants allocate some of their photosynthetically derived carbon to ectomycorrhizal fungi - organisms that colonize roots and provide mineral nutrients to their plant hosts in return for carbon compounds. With the onset of spring, trees will develop leaves for photosynthesis and then drop their leaves in autumn when temperatures decrease and daylight shortens. These seasonal changes in photosynthetic capacity induce fluctuations of carbon stored in tree roots, and may therefore influence the amount of carbon provided to ectomycorrhizal fungi.

Though traditionally considered dependent on living trees for carbon, recent work suggests that ectomycorrhizal fungi may be able to mobilize carbon from soil organic matter and plant litter (i.e. become saprotrophic). Two competing models exist to explain carbon mobilization by ectomycorrhizal fungi. Under the ‘saprotrophy model’, decreased allocation of carbon may induce saprotrophic behavior in ectomycorrhizal fungi, resulting in the decomposition of organic matter to provide the fungus with carbon if the supply from the host plant is inadequate. Alternatively, under the ‘nutrient acquisition model’, decomposition by ectomycorrhizal fungi may instead be driven by the acquisition of nutrients, such as nitrogen and phosphorus, locked within soil organic matter compounds, with carbon mobilization a secondary process.

We tested whether phenology-induced shifts in carbon reserves of fine roots of aspen affect potential activity of carbon-compound degrading extracellular enzymes by ectomycorrhizal fungi. Ectomycorrhizal roots from mature aspen were collected across eight sites in northeastern Alberta, Canada and analyzed during four distinct phenological stages: winter, spring, summer, and autumn. We predicted potential activity of carbon-compound degrading enzymes would be highest when root carbon reserves were lowest, should host phenology induce saprotrophism.

We found activity of EMF-derived carbon-compound degrading enzymes to be relatively constant across phenological stages. Furthermore, low-biomass ectomycorrhizal fungi appear to have a greater ability to degrade complex carbon compounds when compared to high-biomass ectomycorrhizal fungi. These findings support the nutrient acquisition model, and suggest that the degradation of soil organic matter and plant litter by ectomycorrhizal fungi is driven by nutrient foraging rather than saprotrophy.

Image caption: Mature aspen trees during late summer, when leaves are fully expanded and photosynthesizing at full capacity. Carbon allocation to ectomycorrhizal fungi is likely high during this phenological stage. Photo credit: Erin Wiley.
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New ranking algorithm can identify overall pattern from incomplete surveys, providing critical insight into complex problems

Timothy D. Swain, John Chandler, Vadim Backman, Luisa MarcelinoPhoto by Luisa A. Marcelino.

As the third global coral bleaching episode is currently ongoing and expected to kill thousands of square kilometers of coral reefs, our ability to understand why some corals are killed while others survive is hampered by our capacity to consolidate previous knowledge. Corals are a combination of simple animals and algae that work in highly efficient unison to collect sunlight to make food. This association is sensitive to changes in temperature; when stressed by heat, the combination unravels in the bleaching response, leaving corals weakened and starving. Rising ocean temperatures caused by global climate change have made bleaching more frequent and severe, and understanding the mechanisms underlying the bleaching response is an urgent ecological problem. It is known that the algae associated with coral are highly diverse, and that some types are better at helping corals resist thermal stress than others. This insight originates from many experiments and surveys that, for reasons necessitated by the biology of the organisms themselves, can only provide detailed information on small subsets of the algae types; meaning that we know a lot about the relative performance of short lists of algae types, but almost nothing about the relative performance of all types. It turns out that this problem, of having lots of information about the ranking of small partial lists and little information about the ranking of an entire population, is common in many fields including search engines, election schemes, ‘best of’ rankings, and theoretical and applied sciences and engineering. To overcome this problem we devised a new ranking algorithm that can accept these partial lists and return a consensus ranking of all the elements in the lists even when there are disagreements among lists. We also validated the performance and accuracy of the algorithm with known rankings; the algorithm is very robust at uncovering new comparisons absent from the initial lists and has a low misranking error. This novel tool has broad application potential to a variety of ranking problems and will provide critical insight into coral bleaching mechanisms.

Image caption: Photo by Luisa A. Marcelino.
Read the article in full here.

 

Fire impacts on soil organisms

Jennifer L. Soong, Marie Dam, Diana H. Wall, M. Francesca CotrufoImage provided by authors.

Fires occur in nearly all terrestrial ecosystems. The occurrence rate and severity of fires depends on many factors. One important impact of fires is the combustion of aboveground plant material. This plant material would typically die and be considered “litter” to be decomposed by soil microbes and other organisms, such as nematodes, who help to recycle the nutrients held in the litter for subsequent plant production. When plant litter is combusted during a fire, much of its biomass is volatilized and lost from the ecosystem but a small fraction remains as partially burned residues, or the black charred material remaining on the soil surface after a fire. Here we used pyrolized organic matter as a substance resembling the charred material left behind by fires.

We examined how soil microbes, nematodes and plant roots use organic matter from decomposing litter and pyrolized organic matter in order to understand how the alteration of decomposition inputs to the soil by burning affects soil biological processes. We found that while litter provides a carbon and nitrogen food source to soil microbes, nematodes and growing roots, pyrogenic organic matter remains in the soil mostly unused. We also saw that this litter food source shifts the structure of the belowground food web. These results help to explain the impact of fire on belowground biological processes. For example, if aboveground biomass is removed during fires there is less material remaining to fuel belowground organisms, and the partially combusted material remaining is not easily decomposed and recycled.

Image caption: Image provided by authors.
Read the article in full here.

 

Phytopathogens affect plant volatile emissions and the attraction of parasitoid wasps

Camille Ponzio, Berhane T. Weldegergis, Marcel Dicke and Rieta GolsThe parasitic wasp Cotesia glomerata, parasitizing on 1st instar larvae of the large cabbage white butterfly, Pieris brassicae. Photo copyright Hans Smid / Bugsinthepicture.com.

As natural enemies of plant feeding insects, parasitoid wasps lay their eggs in the bodies of these other insects, and develop inside. The wasps find their herbivorous hosts by using plant odors to find the infested plant. When a plant is attacked by an insect herbivore, the volatile odors that it emits are modified, and these changes provide the foraging wasps with important information on the location of its hosts. If more than one species of insect herbivore attacks the plant, this can affect the plant odors, and in turn affect the ability of the wasps to find hosts.

However, plants are attacked not only by insects, but also by plant pathogens, and these can also change the odor of the plants. This has been rarely studied, and researchers usually focus on plant pathogens that cause disease. Yet plants can also be resistant to a pathogen, and this may also affect the emitted plant odors.

We investigated how two strains of a plant pathogen, with the plants resistant to one and susceptible to the other, affected the composition of the induced odors and the ability of the wasps to find their hosts. We studied plants infected either with a pathogen, caterpillar hosts of the wasps, or a combination of both. We found that the two strains produced odors that were different from each other, but that the odors from plants infected with the disease-causing strain were similar to the odors induced by feeding caterpillars. The parasitoid wasps preferred plants that had both caterpillars and a pathogen over plants with only caterpillars, and they were even attracted to odors from plants challenged with only a pathogen.

This research shows that plant pathogens can have as strong influence as insects on plant odors and their use by parasitoids. It is important to combine research on plant-insect and plant-pathogen interactions in the future if we are to have a better understanding of how plants defend themselves against both types of attackers.

Image caption: The parasitic wasp Cotesia glomerata, parasitizing on 1st instar larvae of the large cabbage white butterfly, Pieris brassicae. Photo copyright Hans Smid / Bugsinthepicture.com.
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Linking the respiration of fungal sporocarps with their nitrogen concentration: variation among species, tissues, and guilds

Lidia K. Trocha, Elżbieta Rudy, Weile Chen, Miroslawa Dabert, David M. EissenstatMeasuring respiration of a piece of sporocarp of Lactarius sp. using the the oxygraph: a chamber containing the silver electrode which detects oxygen consumption; photo captured by Lidia Trocha.

Respiration (RS) has been widely correlated with tissue nitrogen concentration in plants. Worldwide results show positive N-RS relationships across plant species, plant functional groups, and plant organs. We wanted to determine if similar responses exist in fungal sporocarps (spore-producing bodies) either among fungal species representing different guilds (ectomycorrhizal, saprotrophic, and parasitic) or between fungal caps and stipes representing different “tissues”.

Similar to plants, fungal sporocarps exhibit positive N-RS relationships across 93 species, which was consistent across fungal guilds, and across fungal “tissues”. However, in contrast to plants, nitrogen concentration could only explain relatively little (26%) of the RS variation among fungal species. This result may reflect fungal sporocarp nitrogen allocation, which may be partially metabolically inactive.

Forest fungi belonging to different guilds (ectomycorrhizal, saprotrophic, and parasitic) gain food through diverse strategies: by decomposition of organic matter (saprotrophic) or through symbiosis with plants (ectomycorrhizal and parasitic). Thus, feeding strategy of a fungus influences fungal metabolic activity as different amounts of energy resources are required depending on the chemical recalcitrance of the food source.

We found that fungal guild can be linked to sporocarp respiration and nitrogen concentration. Saprotrophic species have the fastest respiration and highest N concentration and ectomycorrhizal species have the lowest, with parasites intermediate. We also found that caps are more active than stipes, which reflects sporocarp “organ” specification: the caps are responsible for producing spores, while stipes mostly lift the caps.

Image caption: Measuring respiration of a piece of sporocarp of Lactarius sp. using the the oxygraph: a chamber containing the silver electrode which detects oxygen consumption; photo captured by Lidia Trocha.
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Limited flexibility in heat tolerance suggests vulnerability to climate change

Belinda van Heerwaarden, Vanessa Kellermann and Carla M. SgròPhotograph provided by author.

Rises in average temperature (as much as 2-4° C), as well as increases in the frequency of extreme temperature events, are likely to pose a major risk to many species. Tolerance of high temperatures is flexible (plastic) and can change depending on the temperatures a species encounters prior to experiencing stressfully high temperatures. Whether flexibility (plasticity) in heat tolerance can buffer the increases in temperature predicted with climate change is not known. We examined the plasticity of heat tolerance in tropical and temperate flies exposed to constant or fluctuating temperatures that reflect average temperatures experienced in nature during development (developmental plasticity), as well as after a short term stressful, but not lethal, temperature as adults (hardening plasticity) representing extreme high temperature events. While we observed some increases in heat tolerance when flies were exposed to higher average temperatures during development (developmental plasticity) and extreme temperatures as adults (hardening plasticity), heat tolerance was improved only by a maximum of 1.01° C. These results imply that overheating risk will only be minimally reduced by plasticity in heat resistance. We also found that increased heat tolerance after exposure to short term non-lethal stressful temperatures (hardening) was lower in flies exposed to warmer average developmental temperatures, indicating that increases in heat resistance at warmer temperatures may come at the cost of a reduced capacity to respond to short term extreme heat events via hardening plasticity. This study suggests that plastic increases in heat tolerance, particularly at warmer temperatures, may not be sufficient to keep pace with temperature increases predicted under climate change.

 

Image caption: Photograph provided by author.
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Searching for prey in a three-dimensional environment: hierarchical movements enhance foraging success in northern elephant seals

Taiki Adachi, Daniel P. Costa, Patrick W. Robinson, Sarah H. Peterson, Masato Yamamichi, Yasuhiko Naito and Akinori TakahashiFemale northern elephant seals during moulting season at Año Nuevo State Reserve, CA, USA. Photo taken by T. Adachi in the morning on May 23, 2011.

In nature, prey is often patchily distributed. Therefore, to enhance foraging success, predators are expected to concentrate search paths in areas where prey is more abundant. This style of searching is generally called “area-restricted search (ARS)”, which is characterized by sinuous search paths of predators with increased turning frequency. ARS has been suggested as an optimal search strategy in a patchy environment for both terrestrial and marine predators. However, due to the technological challenge of coupling search paths of animals with records of feeding events (prey captures), it remains unclear if ARS actually enhances foraging success in free-ranging animals, especially in marine animals that forage in a three-dimensional (3D) underwater environment.

Here, we reconstructed fine-scale 3D dive paths of a deep-diving (occasionally over 1000 m) marine predator, the northern elephant seal, coupled with recording feeding events using accelerometers attached on their jaws. Then, we quantified the 3D foraging behavior to test if seals enhance foraging success by employing “volume-restricted search” (VRS, termed for ARS in three-dimensions) while exploring a 3D environment.

Our results showed that most feeding events occurred when seals employed VRS. Also, we found that there was a hierarchical structure to the VRS; most small-VRS (95%) were nested within large-VRS (nested VRS). Importantly, nested VRS had significantly higher feeding rates than non-nested VRS, because nested VRS contained small- and large-VRS with higher and lower feeding rates, respectively. These results provided the first empirical evidence that underwater sinuous search paths (VRS) are strongly linked to higher foraging success, especially when the search paths are hierarchically structured, suggesting that seals forage on prey in a hierarchical patch system where high-density patches at small scales are nested within low-density patches at larger scales.

For all animals that search for prey, it is a central question how to adjust search paths according to the spatial distribution of prey to enhance foraging success. Our results suggest that northern elephant seals enhance foraging success by employing hierarchical decision making to concentrate search paths in areas where prey appeared to be hierarchically structured in patches over a range of 3D spatial scales.

Image caption: Female northern elephant seals during moulting season at Año Nuevo State Reserve, CA, USA. Photo taken by T. Adachi in the morning on May 23, 2011.
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Litter microbial and soil faunal communities stimulated in the wake of a volcanic eruption in a semiarid woodland

Paula Berenstecher, Daniela Gangi, Adelia González-Arzac, M. Laura Martínez, Eliseo J. Chaves, Eduardo A. Mondino and Amy T. AustinMeliquina Valley, Argentina, several months after the massive eruption of the Puyehue volcano in December, 2011.  This site is approximately 70 km from the epicenter of the eruption.  The area is a mixture of natural woodland vegetation and exotic ponderosa pine (Pinus ponderosa) plantations.  Inset shows depth of ash deposition in the woodland ecosystem. Photo courtesy of P. Berenstecher.

Large-scale natural disturbances, such as hurricanes, fires, frosts and volcanic eruptions, are important factors that affect natural ecosystems, but generalities regarding their effects are difficult due to their infrequent and unpredictable nature. Volcanic eruptions figure as one of the most prominent of these natural disturbances, but the effects on microbes and soil fauna (ground-dwelling arthropods, such as ants, beetles or mites, and nematodes, microscopic round-worms) are relatively unknown. These organisms are important because they are key players in the formation of soil organic matter and turnover of nutrients which then become available for plants. We evaluated ecosystem changes induced by the dramatic Puyehue-Cordón Caulle eruption of June 2011 in Patagonia, Argentina. We were interested in how these microbes and soil animals responded to heavy ash deposition in both natural woodland vegetation and a pine plantation in the Meliquina Valley, located 70 km west of the epicenter of the eruption. As ash can be quite abrasive and is, in fact, used as an insecticide, we hypothesized that volcanic ash deposition would have marked negative effects on the soil biota and consequently on decomposition. We were extremely fortunate to have made pre-eruption measurements in the same sites in the year prior to the volcanic eruption, which provided a rare opportunity to make a real comparison before and after the ash deposition.

We measured environmental variables of soil and litter (moisture, pH, organic matter) and biotic variables (abundance of ground-dwelling arthropods, nematodes, microbial biomass and microbial activity in soil and litter) in both natural woodland and pine plantation sites. We were surprised to find that ground-dwelling arthropods actually dramatically increased in abundance after the eruption, while soil nematodes were negatively impacted. More surprising, however, was that evaluating the effects of ash on litter decomposition showed more than doubled rates of carbon turnover in litter from the native woodland. It seems that the effect of the ash deposition may be related to your habitat, with those who reside in the soil being negatively affected while the litter dwelling microbes and fauna were actually favoured by the conditions of the eruption. This study provides insight into the effects of large disturbances on the underappreciated soil biota, and highlights that these disturbances do not always result in the catastrophic effects that we might imagine.

Image caption: Meliquina Valley, Argentina, several months after the massive eruption of the Puyehue volcano in December, 2011. This site is approximately 70 km from the epicenter of the eruption. The area is a mixture of natural woodland vegetation and exotic ponderosa pine (Pinus ponderosa) plantations. Inset shows depth of ash deposition in the woodland ecosystem. Photo courtesy of P. Berenstecher.
Read the article in full here.

 

Using functional responses to quantify interaction effects among predators

Ryan J. Wasserman, Mhairi E. Alexander, Tatenda Dalu, Bruce R. Ellender, Horst Kaiser and Olaf L.F. WeylSouthern mouthbrooder (Pseudocrenilabrus philander- foreground) and banded tilapia (Tilapia sparrmanii- background). Photo provided by authors.

The relationship between prey consumption by a predator and prey availability is known as the functional response. Functional response studies on predators are useful as they provide valuable information on the nature of prey consumption by a predator. For example, the proportion of prey that a predator consumes when there are lots of prey around may be different to the proportion consumed when there are few prey. This is because some predators are better at finding prey at low densities than others, while certain predators are particularly good at eating lots of prey when they are available. Understanding differences amongst predators is important as across most ecosystems, biodiversity levels are changing as a result of extinctions and invasions associated with anthropogenic activities. This is also true for predatory species and many environments have been altered to the point where predatory species have been either lost or gained. It has been shown that predators interact with one another and interactions among predators can diminish or enhance their effects on prey, depending on the nature of the interaction between the predators. These are known as multiple predator effects (MPEs) and are relevant within the context of predator species loss or gain.

While functional response and MPE studies are common in the literature and their value is well recognised, few studies have assessed both aspects of predation simultaneously. In a laboratory study we use three fish species with different functional traits as model predators (bluegill Lepomis macrochirus, southern mouthbrooder Pseudocrenilabrus philander and banded tilapia Tilapia sparrmanii) and assess intra- and inter-specific predator interaction outcomes on predator-prey dynamics. We contrasted the observed functional responses of combinations of predators, of the same or different species, with expected responses based on those of individual predators. We show that prey risk varies as a result of predator-predator effects, both within and between species. This study therefore represents a step closer to real world scenarios where multiple predators interact with one another, and with prey at different prey densities. We therefore propose that the incorporation of predator combinations into classic functional response investigations would be useful for the development of competition and predation ecology.

Image caption: Southern mouthbrooder (Pseudocrenilabrus philander- foreground) and banded tilapia (Tilapia sparrmanii- background). Photo provided by authors.
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Fertilization changes goldenrod’s defensive response to grasshoppers

Karin T. Burghardt Photo credit: Karin T. Burghardt.

Most plants are not able to actively move away from animals that want to eat them, however they are far from passive in their response. Many species can reduce herbivore feeding by producing an arsenal of chemical and structural anti-herbivore defenses. Such resistance may always be produced by a plant at baseline levels or only after an herbivore attacks. Alternatively, a plant can tolerate herbivore damage and simply reallocate resources to promote regrowth, thereby minimizing the negative impact of the herbivore on reproduction. The strategy a plant uses may depend on nutrient availability because the cost-benefit trade-off between growth and defense changes across nutrient environments.

In this study, I investigated how defensive strategy changes across a nutrient (fertilization) gradient within tall goldenrod. This plant is an extraordinarily common species found within abandoned fields and along roadsides across eastern North America. Clones of 9 genotypes (collected from an old-field) were grown in a greenhouse at varying nutrient levels and some were exposed to grasshoppers collected from the same field.

I found that genetically identical individuals changed their defensive strategy across the nutrient gradient. At low nutrient levels, plants tolerated herbivory and exhibited low to moderate levels of baseline resistance. In contrast, fertilized plants did not invest in baseline resistance, opting to wait and invest in high levels of resistance only when attacked by grasshoppers. It is important to note that plant defensive trait changes occur within the context of many other whole-plant changes. Therefore, I also studied how a plant’s defensive strategy changed in concert with 26 other plant traits including leaf nutrient content and belowground allocation.

This study highlights how flexible genetically identical plants can be in terms of resource allocation patterns across developmental environments. In addition, quantifying the way in which a dominant species alters traits in response to nutrients enables us to predict how human-caused nitrogen deposition (a known occurrence in the northeastern U.S.A) will impact old-field communities. Finally, understanding how soil nutrient environment changes plant defensive traits and productivity is of critical importance to agriculturists interested in reducing pesticide use while maximizing yield.

Image caption: Photo credit: Karin T. Burghardt.
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Predator-prey mass ratio revisited: Does preference of relative prey body size depend on individual predator size?

Cheng-Han Tsai, Chih-hao Hsieh and Takefumi NakazawaPhoto provided by authors.

Food webs are complex systems including many species and interactions and thus are difficult to understand. A promising way of understanding food-web dynamics and their responses to environmental changes is to focus on body size relationships between interacting predator and prey, because their relative body sizes (i.e. predator-prey mass ratio, abbreviated as PPMR) largely determine the strength of predator-prey interactions. Specifically, it is expected that predators should not eat too big or too small sized prey. If we know the optimal relative prey size, it may help to simplify the structure of complex food-web models and allow us to more easily assess food-web responses to environmental changes. This optimal relative prey size is called preferred PPMR.

So far, previous studies of several dietary datasets have reported that PPMR increases with predator body size, meaning that large predators consume proportionally smaller prey. Problematically, this pattern contradicts the conventional assumption that all predators should have a similar value of preferred PPMR, and thus those studies have argued that more complex food-web models are needed to better describe food-web dynamics.

However, we point out that this apparent inconsistency arises because previous measurement of PPMR have been based only on dietary data (i.e. realised PPMR in diet) and have not appropriately assessed prey size selectivity of predators (i.e. preferred PPMR) by considering effects of prey composition in the environment. In this study, comparing long-term changes in prey size composition in both the diet and the environment of a fish species, we appropriately assessed preferred PPMR for the first time, and observed that preferred PPMR does not vary with predator body size, in accordance with the original theoretical expectation. Although this is a case study using a single predator species, our findings represent an important first step in establishing size-based food-web studies. In addition, our approach can be generally applied to other species and systems, which would allow us to test the plausibility of previous theoretical predictions based on the assumption of size-invariant preferred PPMR.

Image caption: Photo provided by authors.
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How bark properties promote invertebrate diversity in tree logs during early decay

Juan Zuo, Matty P. Berg , Roy Klein, Jasper Nusselder, Gert Neurink, Orsi Decker, Mariet M. Hefting, Ute Sass-Klaassen, Richard S. P. van Logtestijn, Leo Goudzwaard, Jurgen van Hal1, Frank J. Sterck, Lourens Poorter, Johannes H. C. Cornelissen One incubation plot of LOGLIFE experiment in Hollandse Hout, province of Flevoland, the Netherlands. Photograph by J. Zuo.

Temperate forests accumulate large numbers of tree logs, which play important roles for biodiversity. They host a large number of organisms that need decaying bark or wood for food, shelter or reproduction. Among these organisms, invertebrates are a vital group with a fascinating diversity and an important role in the decay process of dead trees itself. The factors that determine invertebrate community composition in logs are still not clear. In recently dead tree trunks, the attached bark is of critical importance. The large variation in bark structure and tissue quality observed among tree species may determine invertebrate community composition by providing variation in resources and habitats.

We investigated the effects of bark properties, during the early decay stage of logs, on invertebrate community structure of 11 common, temperate tree species in the LOGLIFE ‘common garden’ experiment, in which logs of all these trees were placed in the same forest plots at the same time. We measured several bark properties and studied their effects on six animal groups: earthworms, woodlice, centipedes, millipedes, flies/midges and beetles. We hypothesized that, across tree species, the more different the bark properties were between two species, the more the composition of the animal community would differ as well.

Our tree species varied greatly in seven different bark properties, which had profound effects on the abundance of specific invertebrate groups. The greater the overall difference in the bark properties between tree species, the more dissimilar were the animal communities they supported, and the richer they were together in different invertebrate families. Bark properties have important effects on the composition and diversity of invertebrate communities in recently dead and decaying tree trunks. Our findings indicate that functional diversity in bark properties in decaying logs is likely a good indicator, better than tree species per se, of animal diversity in forests.

Image caption: One incubation plot of LOGLIFE experiment in Hollandse Hout, province of Flevoland, the Netherlands. Photograph by J. Zuo.
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Relative importance of soil properties and microbial community for soil functionality

Manuel Delgado-Baquerizo, Jasmine Grinyer, Peter B. Reich and Brajesh K. SinghImage provided by authors.

Soil ecosystem functionality is usually divided into two groups of functions: broad (i.e. widely conducted by all or most living organisms) and specialized (i.e. conducted by particular groups of organisms). The most widely accepted theories in soil ecology suggest that broad (e.g. respiration) and specialized (e.g. denitrification – reduction of nitrate, ultimately to nitrogen) functions are affected differently by resource availability and microbial communities in terrestrial ecosystems. However, we lack solid empirical data to quantify the relative importance of microbial communities and soil properties in regulating soil functions. Here we conducted a manipulative experiment and used statistical modeling to evaluate the role of soil properties and microbial communities in driving broad and specialized functioning. Our results provide direct experimental evidence that soil microbial community plays an important role in determining the rates of both broad (soil respiration) and specialized (denitrification) functions. In particular, our findings indicate that for broad functioning, soil properties such as total carbon can play a bigger role than the microbial community composition. Contrary to this, bacterial community composition drove the rates of specialized functioning, regardless of soil properties. These results support the most widely accepted soil ecological theories that suggest that broad functions such as soil respiration, which are a product of widely distributed processes across living microorganisms, are limited by both resource availability and microbial abundance. But specialized functioning, which is conducted by particular groups of organisms, may be highly sensitive to changes in microbial community. Such evidence helps advance our understanding of different drivers of soil ecosystem functioning, which will be crucial to developing an ecologically-relevant theory about belowground ecosystem functioning.

Image caption: Image provided by authors.
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Are dive bottom durations good indicators of fur seal foraging success?

Morgane Viviant, Tiphaine Jeanniard-du-Dot, Pascal Monestiez, Matthieu Authier and Christophe GuinetArctic fur seal. Photograph by Christophe Guinet, CEBC UMR 7372 ULR-CNRS.

Foraging models applied to air breathing divers predict that diving predators should optimize the time spent foraging at the bottom of dives, depending on prey encounter rate, distance to the prey patch (depth) and physiological constraints. This hypothesis was tested in free-ranging diving Antarctic fur seal Arctocephalus gazelle, equipped with accelerometers or Hall sensors that recorded mouth-opening events, an indicator of feeding events. 82 % of mouth-openings, defined as prey catch attempts, occurred at the bottom of dives. In accordance with model predictions, fur seals increased their foraging time at the bottom of dives with increasing diving depth, irrespective of the number of mouth-openings events. For dives shallower than 55 m, the mean bottom duration of dives without mouth-opening events was shorter than for dives with mouth-opening events. However, this difference was only due to the occurrence of V-shaped dives with very short bottom durations (0 or 1 s). When those V-shaped dives are removed, bottom duration was no longer related to the presence of prey capture attempts. Thus, the decision to abandon foraging is likely related to other information about prey availability than mouth-opening events (i.e. visual, sensory or acoustic cues), that seals might start collecting during the descent phase. For dives deeper than 55 meters, seals keep on foraging at bottom to maintain a greater diving efficiency as there is no longer any benefit of giving up. Most dives occurred at shallower depths (30-55 m) than the depth of highest foraging efficiency (i.e. of greatest number of mouth-opening events detected per dive, below 60 m). This is likely related to physiological constraints linked to deeper dives. These findings suggests that foraging decisions are more complex than predicted by current theory and highlight the importance of the information collected by the predator during the descent as well as physiological constraints.

Image caption: Arctic fur seal. Photograph by Christophe Guinet, CEBC UMR 7372 ULR-CNRS.
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Stable isotopes reveal the ecology of tropical butterfly larvae.

Erik van Bergen, Henry S. Barlow, Oskar Brattström, Howard Griffiths, Ullasa Kodandaramaiah, Colin P. Osborne and Paul M. BrakefieldEcologists at work. Photo provided by author.

Despite many ecological studies, our understanding of the larval ecology of many tropical butterfly species is very limited. In contrast to adults, caterpillars are mainly active at night and are notoriously hard to spot in the wild. This seriously hampers investigations of the evolution of feeding ecology and potential co-evolutionary interactions between host plants and butterflies. One group of butterfly species that is particularly interesting in the context of plant-herbivore co-evolution is the subtribe Mycalesina (Nymphalidae). These tropical butterflies feed mainly on grasses as larvae and have radiated dramatically in Sub-Saharan Africa, Madagascar and Asia with over 300 extant species.

The commonest form of photosynthesis is called C3, but tropical grasses often have a variant called C4, and the evolutionary history of mycalesine butterflies is expected to be closely tied to the rapid replacement of C3 vegetation by C4 grasslands in the Late Miocene-Pliocene. In contrast to C3 host plants, these C4 grasses tend to have a higher physical toughness and lower nutritional values. Therefore, insect herbivores, such as mycalesine larvae, are expected to avoid C4 grasses when C3 host plants are available. In addition, one would predict that novel feeding adaptations, for instance in jaw morphology or digestive physiology, may have evolved in mycalesines in response to the ecological dominance of C4 grasses in open savannah habitats.

Stable isotope analyses represent an unexploited opportunity to increase our understanding of the larval ecology of mycalesine butterflies. The environmental conditions to which a caterpillar is exposed are imprinted into the exoskeleton of the adult during metamorphosis. By measuring the ratios of several stable isotopes we can recover the information that is ‘recorded’ in leg material (=exoskeleton) of adult butterflies, which are relatively easy to capture in the wild. Here, we show that stable isotopes of carbon provide information about the type of host plant, C3 or C4, which was used by the larvae. In addition, stable isotopes of oxygen reveal how much water vapour was present in the atmosphere during larval development.

The isotopic composition of leg tissue in mycalesine butterflies shows that species that inhabit open C4 grass-dominated environments are quite opportunistic in their larval host plant choice. Nevertheless, we observe that during the dry season, larvae are more likely to use high quality C3 grasses and are exposed to lower levels of water vapour in the atmosphere. Finally, our data reveal that the ability to process C4 grasses is clustered within related groups of mycalesine species, suggesting that C4 grass processing adaptations may have evolved in this subtribe.

Image caption: Ecologists at work. Photo provided by author.
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Mycorrhizal and saprotrophic fungal guilds compete for the same organic substrates but affect decomposition differently

Inga TM Bödeker, Björn D Lindahl, Åke Olson and Karina E ClemmensenThe soil profile of the boreal forest near Sala in middle Sweden in which the field study was conducted. The soil has a 10-25 cm thick organic layer on top of the mineral soil. Photo by KEC.

Communities of litter saprotrophic (decomposer) and mycorrhizal fungi are vertically separated within boreal forest soil profiles, with litter saprotrophs normally confined to the fresh litter on the surface and mycorrhizal fungi dominating the deeper soil layers. It is unclear whether this depth partitioning is maintained exclusively by substrate-mediated niche partitioning, or by competition for space and resources. Improved understanding of the mechanisms driving spatial partitioning of these fungal guilds is critical, as they may affect carbon and nutrient cycling in different ways.

We utilized the spatial separation of litter saprotrophic and mycorrhizal fungal communities to – under field settings – test the potential of these fungal guilds to colonize and exploit organic matter outside their normally realized niche. Natural substrates of three qualities – fresh or partly decomposed litter or humus – were incubated in mesh-bags in both their own and in ‘foreign’ locations in the soil profile. After one and two growing seasons we determined fungal community composition and decomposition activities in the substrates.

During the first growing season, all organic substrates were mainly colonized by fungi native to the soil horizon in which the substrates were incubated. This demonstrated the potential of both fungal guilds to colonize all substrates, and suggests that their colonization under natural circumstances is restricted by competitive interactions. Litter substrates also decomposed more slowly when colonized by root-associated communities than when colonized by saprotrophs, suggesting that ectomycorrhizal fungi are less efficient than saprotrophic fungi in decomposing aboveground litter substrates.

During the second growing season, certain basidiomycetes from both guilds were particularly efficient in localizing and exploiting their native organic substrates although displaced in the vertical profile. This resulted in a complete catch-up in decomposition of litter even when placed in the humus, showing that fungal communities – rather than microenvironmental conditions - were the primary drivers of slow decomposition of litter during the first season. Humus substrates were only slightly decomposed by both fungal guilds, and based on the present study we cannot resolve whether competitive interactions between fungal guilds are important for long-term soil C storage.

Overall, fungal community development during the course of the experiment was determined to similar degrees by vertical placement and by substrate quality. While the importance of substrate quality on decomposer communities and their activities has long been acknowledged, our results suggest that competition and monopolization of spatial domains (as tested by the placement treatment) play a more important role in structuring fungal communities at small scales than previously thought. In natural ectomycorrhiza-dominated forest ecosystems, preferred substrates and territorial distribution of these fungal guilds thus coincide, and competition appears to reinforce the vertical, substrate-dependent partitioning and stabilize vertical community stratification.

At the ecosystem level these findings suggest that ectomycorrhizal fungi through competitive interactions have the potential to indirectly regulate litter decomposition rates by restraining activities of more efficient litter saprotrophs. Vice versa, in situations where the competitive strength of mycorrhizal fungi is compromised – for example after forest clear-cuts – saprotrophs may proliferate and accelerate decomposition processes.

Image caption: The soil profile of the boreal forest near Sala in middle Sweden in which the field study was conducted. The soil has a 10-25 cm thick organic layer on top of the mineral soil. Photo by KEC.
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Ecosystems, Evolution and Plant Soil Feedbacks

Rapid evolution of plants and soil microbes

Casey P. terHorst and Peter C. ZeePhotograph provided by authors.

Ecologists have long appreciated the value of diversity in natural plant communities. Diverse communities function better. Yet, our understanding of the factors that control diversity in communities remains incomplete. We have recently begun to appreciate the important role of microbes in human health; plants too both rely on and battle with microbes in the soil. Plant diversity can affect the soil microbial community, but the microbes also affect plant diversity, in a feedback known as plant-soil feedback (PSF). Because of their short generation times and strong effects on each other’s ecology, plants and microbes can evolve on the scale of weeks to years. Here we review evidence of how changes in plant and microbial traits affect diversity and ecological dynamics in the community. Genetic variation in plant traits and subsequent evolution of those traits can affect traits and species composition of soil microbial communities. Soil microbial communities can, in turn, alter the evolutionary trajectory of plant traits. Finally, we consider how interactions between ecology and evolution might enhance or mitigate the effects of PSF in driving the diversity of natural plant communities.

Image caption: Photograph provided by authors.
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Advances and challenges in the study of ecological networks

Evolutionary history imprinted on species interaction

Guadalupe PeraltaThe leaf veins resemble the shape of species phylogeny which underlies the plant-leafminer interaction. Photo by G. Peralta.

In ecosystems, organisms interact with each other in diverse ways, forming complex webs of relationships. It is well known that the occurrence of interactions among species of a community depends on species co-occurrence and also on their abundance. However, apart from these factors, it has been suggested that the evolutionary history of species might also determine the interactions that occur within a community. If this was the case, information on species relatedness could improve our understanding of the mechanisms driving community structure and dynamics. In addition, if species relatedness is informative of the interactions that species have, this could be used as a tool for determining and predicting the effects that global environmental changes could have on communities. For instance, the effects of an invasive species could be forecast, and potentially reduced, if we could predict how that species would fit into the assemblage of interactions of the invaded community (i.e. if based on the relatedness of the invasive species with other species we could predict its partners).

Therefore, in this paper I review the ecological literature in which species relatedness has been tested as a potential driver of the ensemble of interactions and its structure. It has been shown that species relatedness can affect different aspects of community structure differently and this imprint can also vary depending on the interaction type (e.g. antagonistic vs. mutualistic interactions).

Thus, the evidence confirms that species interactions bear the stamp of their evolutionary history. Understanding the influence that species relatedness has on community assembly can help us to predict how communities might change and how they will function in the future.

Image caption: The leaf veins resemble the shape of species phylogeny which underlies the plant-leafminer interaction. Photo by G. Peralta.
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Neighboring resources can affect the attractiveness of resources occurring in the neighborhood

Thomas A. Verschut, Paul G. Becher, Peter Anderson and Peter A. Hambäck  Photo credit: Sébastien Lebreton.

Plants often differ in their quality as a food resource for insects. As many insects find food through smell, a plant with a very attractive smell will attract a higher number of insects than a plant with a less attractive smell. However, when an attractive plant grows next to an unattractive plant it can lead to an increased number of insects visiting the unattractive plant, which is known as associational susceptibility. Moreover, an attractive plant could also lower the number of visits to the less attractive plant, which is known as associational resistance. These associational effects have been commonly observed for pollinators visiting flowers and herbivorous insects feeding on different plant species. However, it is not fully understood how mixtures of different resources lead to different outcomes of associational effects.

We tested how the density and frequency of different resources could lead to associational susceptibility or associational resistance using the common fruit fly, Drosophila melanogaster. Fruit flies are strongly attracted to fermenting fruits, which contain odours that are also found in balsamic vinegar. Therefore, we used balsamic vinegar to mimic food resources that differed in their attractiveness. With these resources we created patches containing different frequencies of attractive and less attractive resources.

Firstly, we found that attractiveness of a resource patch depends on which resources it contains, but that there is threshold at which increasing the number of resources does not result in a higher attractiveness of the patch. Secondly, we found that fruit flies are always more attracted to the resource that smells most attractive in the patch. Because a higher number of flies visited the more attractive resource in the mixed patches, compared to when the more attractive resource occurred on its own, it experienced associational susceptibility. Moreover, the less attractive resource experienced associational resistance, as the number of fly visits was lower in mixed patches. The strength of this interaction increased with a decreasing frequency of the more attractive resource. These findings can have important implications for managing plants in mixed environments and can help to predict the relative numbers of insects visiting plants growing in the same area.

Image caption: Photo credit: Sébastien Lebreton.
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Advances and challenges in the study of ecological networks

Who interacts with whom? A common framework for identifying linkage rules across different types of interactions

Ignasi Bartomeus, Dominique Gravel, Jason M. Tylianakis, Marcelo A. Aizen, Ian A. Dickie and Maud Bernard-Verdier Eucera bee visiting Cistus salvifolius. Curro Molina.

To understand ecological communities of plants and animals, we need more than a list of species. We need to know how the species interact. In fact, most important ecological processes are mediated by an interaction. Take for instance a flowering plant and a bee. Only their interaction allows both bees and plants to reproduce. Other interactions involve predators and their prey, or herbivores and plants.

We know that big fish eat small fish and that pollinators with long tongues tend to visit plants with deep flowers. However, quantifying who interacts with whom is not an easy task. For example, predators eat prey smaller than themselves, but not if the prey becomes too small for them. Similarly, pollinators with short tongues cannot reach deep flowers, but long-tongued pollinators may not be constrained to any type of flower.

In this paper, we review recent advances in predicting interactions from species co-occurrence and develop a probabilistic model for inferring trait matching. We model the probability that two species interact based on the matching of their traits while taking into account species abundances. The model presented uses empirical data to understand why two species interact or not. We exemplify its use with three case studies, but the model can be applied to a great range of mutualistic and antagonistic interactions, from grasshoppers chewing on plant leaves to pollinators drinking nectar. Understanding the linkage rules is important to predict how the web of life is organized, especially in the face of the human-induced environmental changes we are experiencing.

Image caption: Eucera bee visiting Cistus salvifolius. Curro Molina.
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Energy expenditure of adult green turtles at sea

Manfred R. Enstipp, Katia Ballorain, Stéphane Ciccione, Tomoko Narazaki, Katsufumi Sato and Jean-Yves GeorgesAdult green turtle foraging at a seagrass meadow in Mayotte. Credit: Manfred Enstipp.

All living organisms must obtain food from the environment to provide energy for their daily lives. Understanding how much energy organisms need for their various activities is a central topic studied by eco-physiologists. In the case of marine turtles, knowing their energy needs during the different phases of their life at sea is essential for their conservation, which critically depends on successful reproduction. In these reptiles, reproduction is typically associated with long-distance migration and only occurs every few years. It is an enormous physical task and requires substantial energy reserves, which are build up at the foraging grounds. If a turtle has insufficient energy reserves, it will not be able to engage in costly reproduction, with consequences for population/conservation status.

Using a novel technique (attaching small accelerometry dataloggers to turtles), we studied activity patterns and energy expenditure of adult green turtles foraging year-round at a seagrass meadow in Mayotte and during simulated migration (displacing a turtle from its nesting beach) off Mohéli, in the south-western Indian Ocean. We found a clearly structured activity pattern for turtles at the foraging site that persisted throughout the year. During daylight hours turtles foraged on the shallow seagrass meadow (many short/shallow dives), while at night they rested on the inner reef slope (few long/deep dives). Energy expenditure at the foraging site during the austral summer was low (~1.6 times the value at rest) and declined even further with decreasing water temperatures during the austral winter. By contrast, upon its oceanic release, the displaced turtle swam continuously towards its nesting beach, conducting shallow/short dives during the day, which, mostly at night, were interspersed with few deep/long dives. Energy expenditure during this simulated migration was greatly increased to ~3 times the value at rest, indicating the costliness of such undertaking. Using a novel technique, we were able to study the energy needs of adult green turtles in great detail and under natural conditions. We show that continuous feeding during daylight hours at their foraging site, at low energetic costs, allows these turtles to gradually build up energy reserves needed for migration and reproduction.

Image caption: Adult green turtle foraging at a seagrass meadow in Mayotte. Credit: Manfred Enstipp.
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Author-suggested reviewers: Gender differences and influences on the peer review process at an ecology journal

Charles Fox, C. Sean Burns, Anna Muncy and Jennifer MeyerImage from  “What is a journal and a peer reviewed article?” (Northeastern Illinois University Ronald Williams Library)

Peer review is the primary method by which journals evaluate the quality and importance of submitted manuscripts. Identifying suitable reviewers, and then recruiting them to review, is one of the most challenging parts of an editor’s job. Authors should know best who is qualified to review their papers; thus, to help editors find suitable reviewers, many journals allow or require authors to suggest names of preferred and non-preferred reviewers. However, authors also have a strong incentive to suggest reviewers that they expect to review their paper positively.

In this study, we examine the reviewers that are suggested by authors as preferred (those that authors would like to review their manuscript) and non-preferred (those that authors request not be invited to review their paper), the use of these suggestions by editors, and their influence on the peer review process and outcomes at the journal Functional Ecology. We also examined how gender of the participants (author, editor and reviewer) influences the role of preferred reviewers in the peer review process.

Most authors suggest preferred reviewers, but few suggest non-preferred reviewers. Most author-preferred reviewers are male, but the proportion of women among author suggestions increased from a low of 15% in 2004 to a high of 25% in 2014. Male and female authors did not differ in how likely they were to suggest preferred reviewers, but female authors suggest more female reviewers (~28%, averaged across years) than do male authors (~21%). Women that were suggested as preferred reviewers were more likely to be chosen by editors as desired reviewers than were men suggested by authors. We found no evidence that editor gender, seniority or length of service as an editor for Functional Ecology affected how likely they were to use author-suggested reviewers.

Of reviewers invited to review, those that were suggested by authors were more likely to respond to the editors' review invitations but were not more likely to agree to review. Most strikingly, author-preferred reviewers rated papers much more positively than did editor-selected reviewers, and papers reviewed by author-preferred reviewers were much more likely to be invited for revision than were papers reviewed by editor-selected reviewers. This difference was not influenced by the gender of the participants in the process.

Suggesting preferred reviewers clearly benefits authors – preferred reviewers rate papers significantly more positively (on average) than do editor-selected reviewers, improving the chances that a paper will be published. We thus recommend that authors always suggest preferred reviewers if given the option to do so by a journal. Journals and editors, by contrast, should consider who proposed the reviewer, and possible biases, when deciding whether to use author-suggested reviewers and when evaluating reviewer comments and scores. Highly-selective journals – those whose decisions emphasize broad general interest, significance and novelty – might consider eliminating the practice of allowing or requiring authors to suggest their own reviewers.

Image caption: Image from “What is a journal and a peer reviewed article?” (Northeastern Illinois University Ronald Williams Library).
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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.
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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.

 

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.

 

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.
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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.
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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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