Temporal Variation in Danger Drives Antipredator Behavior: The Predation Risk Allocation Hypothesis.

The rapid response of animals to changes in predation risk has allowed behavioral ecologists to learn much about antipredator decision making. A largely unappreciated aspect of such decision making, however, is that it may be fundamentally driven by the very thing that allows it to be so readily studied: temporal variation in risk. We show theoretically that temporal variability in risk leaves animals with the problem of allocating feeding and antipredator efforts across different risk situations. Our analysis suggests that an animal should exhibit its greatest antipredator behavior in high-risk situations that are brief and infrequent. An animal should also allocate more antipredator effort to high-risk situations and more feeding to low-risk situations, with an increase in the relative degree of risk in high-risk situations. However, the need to feed leaves an animal with little choice but to decrease its allocation of antipredator effort to high-risk situations as they become more frequent or lengthy; here, antipredator effort in low-risk situations may drop to low levels as an animal allocates as much feeding as possible to brief periods of low risk. These conclusions hold under various scenarios of interrupted feeding, state-dependent behavior, and stochastic variation in risk situations. Our analysis also suggests that a common experimental protocol, in which prey animals are maintained under low risk and then exposed to a brief "pulse" of high risk, is likely to overestimate the intensity of antipredator behavior expected under field situations or chronic exposure to high risk.