Understanding how the combined effects of multiple predators affect shared prey is a long-standing goal of ecology. We know that different predators can function independently, synergistically, or antagonistically to affect prey survival and that synergistic and antagonistic effects are often mediated through predator induced changes in prey behavior and morphology. However, what is less well known is how variation in predator exposure affects 1) the expression of predator induced phenotypes in prey and 2) how variation in predation risk affects the amount of among individual phenotypic variation that is expressed. In this study we examine how different amounts of variation in predation risk affects among-individual phenotypic variation and survival in prey. Specifically, we recorded the behavior of pond snails (Physa acuta) after exposure to non-lethal cues of predation risk from crayfish (Procambarus clarkii) and fish (Lepomis macrochirus) administered with zero (constant fish or crayfish), low, and high amounts of variation. Behaviors were recorded over a period of 6.5 hours per day for 12 days. We also quantify how environmental and individual variation affects snail reproduction and survival when exposed to lethal predators following the behavioral assays.
Results/Conclusions
We use double hierarchical generalized linear models (DHGLM) to analyze treatment effects on individual variation in behavior. DHGLM are hierarchical models that allow for explicit modeling of residual variance as a function of both fixed and random effects. We find effects of increasing variation in the predator environment on 1) among-individual variation in average behavior; 2) treatment average within-individual variation; 3) variation among treatments in the amount of within-individual variation; 4) effects of environmental variation on both reproductive and survival rates. Our results highlight among-individual variation as a potentially new form of behavioral plasticity in response to variable environments that may have important consequences for understanding the structure and function of food web interactions.