Prey nutritional condition: A common influence of antipredator behavior and the "ecology of fear"?

Background/Question/Methods

A prey animal’s quandary is to survive predation while also eating enough food to meet its energy requirements. The behavioral tradeoff between these two needs is mediated by prey body condition. Many ecological conditions and biological processes, such as resource scarcity and reproduction, tend to reduce prey body condition. A large body of theory predicts that when prey animals are in poor condition, and are pressed by hunger, their antipredator behaviors are weak or nonexistent. The dependency of antipredator behavior on body condition might commonly introduce bottom-up limitations on predation risk effects. Although familiar to behavioral ecologists, the mediating role of prey body condition has yet to be integrated into our conceptualization of the population- and community-level effects of predation risk. We synthesized theoretical and empirical studies that explored the influence of body condition on antipredator behavior across a variety of systems. 

Results/Conclusions

We found that predictions of a well-known patch-use model of Brown and Kotler (2004), where antipredator behaviors are predicated partly on the marginal value of new energy gained by prey, was broadly supported by studies of fish, mammals, birds, reptiles, amphibians, and invertebrates. In 96% (44/46) of the studies, prey animals with high energy reserves responded more strongly to a predation stimulus than individuals with low energy reserves. This relationship was robust to differences in study design, including differences in the manipulation of prey condition and predation risk, and in the specific behavioral response being measured. We use several examples from recent studies of temperate ungulates, which experience strong seasonal and interannual nutritional bottlenecks, to illustrate these findings. Antipredator behaviors can carry costs for prey populations and benefits for the plant communities they feed upon, and these risk effects are thought to be strong and widespread. However, we suggest that the countervailing influence of bottom-up limitations on prey body condition and behavior – largely overlooked to date in studies conducted at the population and community level – must be more fully integrated into existing theory if we are to fully resolve the context-dependency of predation risk effects.