Fleeing and hiding under simultaneous risks and costs

Prey evaluate risk implied by a predator during its approach, intrinsic prey features, and environmental factors to weigh risk against costs. Most studies of escape and hiding time in refuge focus on a single factor, but prey that ignore other factors may soon be dead. Two hypotheses make different predictions about additivity versus interaction of risk–cost factors. The risksensitivity hypothesis predicts that multiple factors have additive effects, but optimality theory suggests that interaction is more common. In the only previous study, flight initiation distance (FID ¼ predator–prey distance when escape begins) was affected interactively by 2 risk factors (predator approach speed and directness) but additively by a risk and an escape cost (approach speed and food presence). I predicted that effects of approach speed and other risk factors interact because differences in risk are likely to increase more rapidly with increase in approach speed than other factors. FID by lizards that I approached increased interactively with approach speed and directness in the Sceloporus virgatus and speed and predator persistence in Sceloporus jarrovii. During indirect approaches, fewer S. virgatus fled, and they ran shorter distances. A review of effects of multiple risks and costs on FID and hiding time revealed far more frequent interactive than additive effects between 2 risk factors, as predicted by optimality theory. Additive and interactive effects were equally common between a risk and a cost factor. Findings for some factors differ between FID and hiding time and in other ways. I propose hypotheses to explain some differences. Key words: escape behavior, flight initiation distance, hiding time, refuge use, squamata. [Behav Ecol] P rey must cope with predation risk posed by predators that vary in many ways relevant to escape decisions, as well as assess environmental factors and intrinsic prey characteristics affecting risk. Prey that can evaluate multiple risks simultaneously should have higher long-term survival than prey that react to only a single factor. Experiments on escape behavior usually examine effects of single risk factors and control others, but it may be anticipated that many prey can take into account multiple risk factors operating during short-term encounters with predators. Prey able to respond to multiple risks might treat them additively or interactively (Smith and Belk 2001). Studies bearing on this issue for pairs of risk factors or factors affecting risk and cost of escaping or hiding (lost opportunities) are limited to lizards and turtles. Although information is beginning to accumulate about effects of simultaneous risk on escape behavior (Table 1), conditions leading to additivity or interaction between the factors are poorly understood. Escape theory predicts flight initiation distance (FID ¼ distance between predator and prey when escape begins) and sometimes distance fled based on risks and costs (Ydenberg and Dill 1986; Cooper and Frederick 2007a). Predictions are made from expected fitness determined jointly by multiple factors that affect predation risk and escape cost. Without knowledge of the form of functions relating fitness to distance between predator and prey, escape theory does not predict whether effects are additive or interactive.