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1. Quantifying the effects of intraspecific variation on predator feeding rates through nonlinear averaging

   https://doi.org/10.1111/1365-2435.13802  

   Coblentz, Kyle E. ; Merhoff, Stephanie ; Novak, Mark ( June 2021 , Functional Ecology)

   Theory suggests that intraspecific trait variation will alter species interaction strengths through nonlinear averaging when interaction strengths are nonlinear functions of individuals' traits. This effect is expected to be widespread, yet what factors mediate its magnitude in nature and hence its potential effects on ecosystems and communities are unclear.

   We sought to quantify how nonlinear predator functional responses, variation in prey densities and counteracting variation in attack rates and handling times among predator individuals of similar body size alter their population‐level feeding rates through nonlinear averaging in a natural system, and to determine the processes influencing the net magnitude of this effect.

   We used a field caging experiment in the rocky intertidal of Oregon, USA to quantify attack‐rate variation and feeding rates of the whelkNucella ostrinaon its barnacle and mussel prey. We also used empirically parameterized simulations to examine the effects of handling‐time variation among individuals on population‐level feeding rates.

   Within cages, individual attack‐rate variation reduced population‐level whelk feeding rates. However, the magnitude of this reduction differed among prey species and cages depending on cage‐specific magnitudes of attack‐rate variation and functional‐response nonlinearity. The inferred effects of handling‐time variation among individuals were of smaller magnitude than those of attack‐rate variation, yet counteracted them to cause a net weakening of the effect of individual attack‐rate variation on population‐level feeding rates. Across cages, attack‐rate and prey‐density variation had non‐additive effects that produced greater feeding‐rate reductions at the experiment scale relative to the cage scale.

   Our results indicate that the effects of trait variation via nonlinear averaging depend critically on the features of systems that determine the magnitudes of nonlinearities and trait variation. Because of counteracting trait variation, nonlinear‐averaging effects may be quite complex, involving both the variances and covariances of all traits and environmental variables influencing the ecological process of interest.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Ontogenetic diversity buffers communities against consequences of species loss

   https://doi.org/10.1111/1365-2656.13470  

   Rudolf, Volker H. W. ; Eveland, Lauren ( March 2021 , Journal of Animal Ecology)

   Biodiversity can be measured at multiple organizational scales. While traditional studies have focused at taxonomic diversity, recent studies have emphasized the ecological importance of diversity within populations. However, it is unclear how these different scales of diversity interact to determine the consequence of species loss.

   Here we asked how predator diversity and presence of ontogenetic diversity within predator populations influences community structure. Ontogenetic diversity arises from shifts in the traits and ecology of individuals during ontogeny and it is one of the biggest sources of intraspecific diversity. However, whether it dampens or strengthens the negative consequences of with species loss is poorly understood.

   To study the interaction of species diversity and ontogenetic diversity, we experimentally manipulated predator species diversity and diversity of developmental stages within focal predator species and analysed their joint effect on predator and prey survival, biomass and prey community structure in experimental pond systems.

   While individual effects of ontogenetic diversity were often species specific, losing predator species from the community often had a much smaller or no effect on prey survival, biomass or community structure when all predator populations had high ontogenetic diversity. Thus, ontogenetic diversity within populations buffered against some of the consequences of biodiversity loss at higher organizational levels. Because the experiment controlled mean per capita size and biomass across structured versus unstructured populations, this pattern was not driven by differences in biomass of predators. Instead, results suggest that effects were driven by changes in the functional roles and indirect interactions across and within species. This indicates that even if all environmental conditions are similar, differences in the intrinsic structure of populations can modify the consequences of biodiversity loss.

   Together, these results revealed the importance of ontogenetic diversity within species for strengthening the resilience of natural communities to consequences of biodiversity loss and emphasize the need to integrate biodiversity patterns across organizational scales.

    

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3. Body size, but not age‐at‐maturation or context, affects the expression of predator‐induced behavioural plasticity in female green swordtails ( Xiphophorus hellerii )

   https://doi.org/10.1111/eth.12974  

   DiSciullo, Rachael A. ; Basolo, Alexandra L. ; Goymann, ed., Wolfgang ( October 2019 , Ethology)

   Behavioural plasticity is a form of reversible phenotypic plasticity in which a genotype can express different behavioural phenotypes under different environmental conditions. Though an interest in among‐individual differences in behavioural plasticity has flourished in recent decades, few studies have considered the effects of intrinsic factors, such as life‐history or morphological traits, in tandem with extrinsic factors, such as presence of conspecifics in different social contexts, on predator‐induced behavioural plasticity. Here, we present a study conducted with female green swordtail fishes,Xiphophorus hellerii, designed to assess the effects of age‐at‐maturation and body size on the expression of predator‐induced behavioural plasticity in two social contexts: (a) female‐only (two females) and (b) female‐and‐male (two females and a male). We further examined the extent to which individual expression of behavioural plasticity is consistent across these two social contexts. We found that in the presence of a predator, focal females were more timid in response to the stimulus and more tolerant of the non‐focal female, and small females expressed this change from bold/less tolerant to timid/more tolerant to a greater degree than large females, regardless of age‐at‐maturation. However, individuals were not consistent in the degree or direction of plasticity expressed in the behaviours of interest between the female‐only and the female‐and‐male context. Here, we show that within‐ and among‐individual differences in behavioural expression are common but inconsistent. How intrinsic and extrinsic factors independently or together drive expression of plasticity in antipredator and agonistic behaviours is varied and warrants further study.

    

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4. Variability in environmental persistence but not per capita transmission rates of the amphibian chytrid fungus leads to differences in host infection prevalence

   https://doi.org/10.1111/1365-2656.13612  

   Rumschlag, Samantha L. ; Roth, Sadie A. ; McMahon, Taegan A. ; Rohr, Jason R. ; Civitello, David J. ( November 2021 , Journal of Animal Ecology)

   Heterogeneities in infections among host populations may arise through differences in environmental conditions through two mechanisms. First, environmental conditions may alter host exposure to pathogens via effects on survival. Second, environmental conditions may alter host susceptibility, making infection more or less likely if contact between a host and pathogen occurs. Further, host susceptibility might be altered through acquired resistance, which hosts can develop, in some systems, through exposure to dead or decaying pathogens and their metabolites. Environmental conditions may alter the rates of pathogen decomposition, influencing the likelihood of hosts developing acquired resistance.

   The present study primarily tests how environmental context influences the relative contributions of pathogen survival and per capita transmission on host infection prevalence using the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) as a model system. Secondarily, we evaluate how environmental context influences the decomposition of Bd because previous studies have shown that dead Bd and its metabolites can illicit acquired resistance in hosts. We conducted Bd survival and infection experiments and then fit models to discern how Bd mortality, decomposition and per capita transmission rates vary among water sources [e.g. artificial spring water (ASW) or water from three ponds].

   We found that infection prevalence differed among water sources, which was driven by differences in mortality rates of Bd, rather than differences in per capita transmission rates. Bd mortality rates varied among pond water treatments and were lower in ASW compared to pond water.

   These results suggest that variation in Bd infection dynamics could be a function of environmental factors in waterbodies that result in differences in exposure of hosts to live Bd. In contrast to the persistence of live Bd, we found that the rates of decomposition of dead Bd did not vary among water sources, which may suggest that exposure of hosts to dead Bd or its metabolites might not commonly vary among nearby sites. Ultimately, a mechanistic understanding of the environmental dependence of free‐living pathogens could lead to a deeper understanding of the patterns of outbreak heterogeneity, which could inform surveillance and management strategies.

    

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5. How climate impacts the composition of wolf‐killed elk in northern Yellowstone National Park

   https://doi.org/10.1111/1365-2656.13200  

   Wilmers, Christopher C. ; Metz, Matthew C. ; Stahler, Daniel R. ; Kohl, Michel T. ; Geremia, Chris ; Smith, Douglas W. ; Dantzer, ed., Ben ( March 2020 , Journal of Animal Ecology)

   While the functional response of predators is commonly measured, recent work has revealed that the age and sex composition of prey killed is often a better predictor of prey population dynamics because the reproductive value of adult females is usually higher than that of males or juveniles.

   Climate is often an important mediating factor in determining the composition of predator kills, but we currently lack a mechanistic understanding of how the multiple facets of climate interact with prey abundance and demography to influence the composition of predator kills.

   Over 20 winters, we monitored 17 wolf packs in Yellowstone National Park and recorded the sex, age and nutritional condition of kills of their dominant prey—elk—in both early and late winter periods when elk are in relatively good and relatively poor condition, respectively.

   Nutritional condition (as indicated by per cent marrow fat) of wolf‐killed elk varied markedly with summer plant productivity, snow water equivalent (SWE) and winter period. Moreover, marrow was poorer for wolf‐killed bulls and especially for calves than it was for cows.

   Wolf prey composition was influenced by a complex set of climatic and endogenous variables. In early winter, poor plant growth in either yeartort − 1, or relatively low elk abundance, increased the odds of wolves killing bulls relative to cows. Calves were most likely to get killed when elk abundance was high and when the forage productivity they experienced in utero was poor. In late winter, low SWE and a relatively large elk population increased the odds of wolves killing calves relative to cows, whereas low SWE and poor vegetation productivity 1 year prior together increased the likelihood of wolves killing a bull instead of a cow.

   Since climate has a strong influence on whether wolves prey on cows (who, depending on their age, are the key reproductive components of the population) or lower reproductive value of calves and bulls, our results suggest that climate can drive wolf predation to be more or less additive from year to year.

    

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