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1. Keystone predation: trait‐based or driven by extrinsic processes? Assessment using a comparative‐experimental approach

   https://doi.org/10.1002/ecm.1436  

   Menge, Bruce A. ; Foley, Melissa M. ; Robart, Matthew J. ; Richmond, Erin ; Noble, Mae ; Chan, Francis ( December 2020 , Ecological Monographs)

   Keystone predation can be a determinant of community structure, including species diversity, but factors underlying “keystoneness” have been minimally explored. Using the system in which the original keystone, the sea starPisaster ochraceus, was discovered, we focused on two potential (but overlapping) determinants of keystoneness: intrinsic traits or state variables of the species (e.g., size, density), and extrinsic environmental parameters (e.g., prey productivity) that may provide conditions favorable for keystone predator evolution. Using a comparative‐experimental approach, with repeated field experiments at multiple sites across a variable coastal environment, we tested predation rates, or how quickly predators consumed prey, and predation effects, or community response to predator presence or absence. We tested five hypotheses: (H₁) predation rates and effects will vary in space but not time; (H₂) per population predation rates will vary primarily with individual traits and population variables; (HJHH₃) per capita predation rates will vary only with individual traits; (H₄) predation effects will vary with traits, variables, and external drivers; and (H₅) as predicted by the keystone predation hypothesis, diversity will vary unimodally with predation pressure. As hypothesized, predation rates differed among sites but not over time (H₁), and in caging exclusion experiments, predation effect varied with both intrinsic and extrinsic factors (H₄). Unexpectedly, predation rates varied with both intrinsic and extrinsic (H₂, per population), or only with extrinsic (H₃, per capita) factors. Further, in large‐plot exclusion experiments, predation effect was most closely associated with individual traits (contraH₄). Finally, taxon diversity varied unimodally with proxies of predation pressure (sessile prey abundance) and was sensitive to extrinsic factors (mussel growth, temperature, and upwelling,H₅). Hence, keystoneness depended on predator individual traits, predator population variables, and environmental parameters. However, temporal differences in caging experiments suggested that environmental characteristics underlying prey dynamics may be preeminent. Compared to prior experiments, predation was weaker with low prey input compared to periods with high prey input. Collectively, our results suggest that keystone predator evolution depends on the coalescence of species‐specific characteristics, and environmental parameters favoring high prey productivity. Our approach may be a model for future studies exploring the generality of keystoneness.

    

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2. Asymmetrical effects of temperature on stage‐structured predator–prey interactions

   https://doi.org/10.1111/1365-2435.13777  

   Davidson, Andrew T. ; Hamman, Elizabeth A. ; McCoy, Michael W. ; Vonesh, James R. ; Marshall, ed., Katie ( March 2021 , Functional Ecology)

   Warming can impact consumer–resource interactions through multiple mechanisms. For example, warming can both alter the rate at which predators consume prey and the rate prey develop through vulnerable life stages. Thus, the overall effect of warming on consumer–resource interactions will depend upon the strength and asymmetry of warming effects on predator and prey performance.

   Here, we quantified the temperature dependence of both (a) density‐dependent predation rates for two dragonfly nymph predators on a shared mosquito larval prey, via the functional response, and (b) the development rate of mosquito larval prey to a predator‐invulnerable adult stage. We united the results of these two empirical studies using a temperature‐ and density‐dependent stage‐structured predation model to predict the effects of temperature on the number of larvae that survive to adulthood.

   Warming accelerated both larval mosquito development and increased dragonfly consumption. Model simulations suggest that differences in the magnitude and rate of predator and prey responses to warming determined the change in magnitude of the overall effect of predation on prey survival to adulthood. Specifically, we found that depending on which predator species prey were exposed to in the model, the net effect of warming was either an overall reduction or no change in predation strength across a temperature gradient.

   Our results highlight a need for better mechanistic understanding of the differential effects of temperature on consumer–resource pairs to accurately predict how warming affects food web dynamics.

   A freeplain language summarycan be found within the Supporting Information of this article.

    

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3. Predator hunting modes and predator–prey space games

   https://doi.org/10.1111/eth.12998  

   Luttbeg, Barney ; Hammond, John I. ; Brodin, Tomas ; Sih, Andrew ; Wright, ed., Jonathan ( December 2019 , Ethology)

   Predators and prey are often engaged in a game where their expected fitnesses are affected by their relative spatial distributions. Game models generally predict that when predators and prey move at similar temporal and spatial scales that predators should distribute themselves to match the distribution of the prey's resources and that prey should be relatively uniformly distributed. These predictions should better apply to sit‐and‐pursue and sit‐and‐wait predators, who must anticipate the spatial distributions of their prey, than active predators that search for their prey. We test this with an experiment observing the spatial distributions and estimating the causes of movements between patches for Pacific tree frog tadpoles (Pseudacris regilla), a sit‐and‐pursue dragonfly larvae predator (Rhionaeschna multicolor), and an active salamander larval predator (Ambystoma tigrinum mavortium) when a single species was in the arena and when the prey was with one of the predators. We find that the sit‐and‐pursue predator favors patches with more of the prey's algae resources when the prey is not in the experimental arena and that the prey, when in the arena with this predator, do not favor patches with more resources. We also find that the active predator does not favor patches with more algae and that prey, when with an active predator, continue to favor these higher resource patches. These results suggest that the hunting modes of predators impact their spatial distributions and the spatial distributions of their prey, which has potential to have cascading effects on lower trophic levels.

    

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4. Warming and top‐down control of stage‐structured prey: Linking theory to patterns in natural systems

   https://doi.org/10.1002/ecy.4213  

   Davidson, Andrew T. ; Stunkle, C. Ryland ; Armstrong, Joshua T. ; Hamman, Elizabeth A. ; McCoy, Michael W. ; Vonesh, James R. ( December 2023 , Ecology)

   Warming has broad and often nonlinear impacts on organismal physiology and traits, allowing it to impact species interactions like predation through a variety of pathways that may be difficult to predict. Predictions are commonly based on short‐term experiments and models, and these studies often yield conflicting results depending on the environmental context, spatiotemporal scale, and the predator and prey species considered. Thus, the accuracy of predicted changes in interaction strength, and their importance to the broader ecosystems they take place in, remain unclear. Here, we attempted to link one such set of predictions generated using theory, modeling, and controlled experiments to patterns in the natural abundance of prey across a broad thermal gradient. To do so, we first predicted how warming would impact a stage‐structured predator–prey interaction in riverine rock pools betweenPantalaspp. dragonfly nymph predators andAedes atropalpusmosquito larval prey. We then described temperature variation across a set of hundreds of riverine rock pools (n = 775) and leveraged this natural gradient to look for evidence for or against our model's predictions. Our model's predictions suggested that warming should weaken predator control of mosquito larval prey by accelerating their development and shrinking the window of time during which aquatic dragonfly nymphs could consume them. This was consistent with data collected in rock pool ecosystems, where the negative effects of dragonfly nymph predators on mosquito larval abundance were weaker in warmer pools. Our findings provide additional evidence to substantiate our model‐derived predictions while emphasizing the importance of assessing similar predictions using natural gradients of temperature whenever possible.

    

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5. 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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