The relationship between predation risk and antipredator responses in larval anurans

Organisms that produce alternative, nondiscrete phenotypes in response to environmental conditions are expected to alter their phenotypes in relation to the degree of environmental change. This idea has been applied to the evolution of antipredator responses by prey, in which it has been hypothesized that prey should respond more strongly to predators that pose greater mortality risk. In a companion paper, I quantified predator-induced behavioral and morphological responses in six species of larval anurans across five different predator environments and found that these responses were prey- and predator-specific. In the present study, I addressed whether the responses were related to the level of predation risk posed by each of the predators. Within each prey species, I found that different predators posed different levels of predation risk; within each predator species, different prey species experienced different levels of risk. The differences in predation risk could be understood mechanistically after I quantified differences among predators in their ability to capture, handle, and consume prey and differences among prey in behavior and morphology. Using multivariate analyses, I found that predation risk had no significant effect on how a given prey responds to predators, although there were significant univariate behavioral effects; higher predation risk was related to greater decreases in activity and greater spatial avoidance. I also examined the relationship between risk and response across the six prey species within a predator treatment and found that higher predation risk across species leads to greater decreases in activity in the presence of Umbra and greater increases in tail depth in the presence of Anax. Thus, while previous studies have found relationships between predation risk and prey response when focusing on relatively few species, few predators, and a single trait, this more powerful test using 30 predator-prey combinations and nine traits suggests that the relationship is not well supported. This finding arises from the fact that larval anurans, as well as many other taxa, exhibit predator- and prey-specific behavioral and morphological changes in response to predator- and prey-specific risk.