SIMULTANEOUS RISKS AND DIFFERENCES AMONG INDIVIDUAL PREDATORS AFFECT REFUGE USE BY A LIZARD, LACERTA MONTICOLA

Abstract

Optimal emergence theory predicts decisions by prey about when to emerge from refuge based on the assumption that optimal time to emerge is determined by the balance between predation risk and costs of the response to it. Tests have verified the predictions for a variety of risk and cost factors, but have focused on single factors, whereas prey must be able to assess the overall risk and cost based on several factors acting simultaneously. In a factorial experiment in which two of us simulated predators, we tested effects of three simultaneous factors, predator approach speed, directness of approach, and individual differences between predators, on time spent in refuge after escaping by the Iberian rock lizard, Lacerta monticola. Effects of approach speed and directness were significant, the lizards delaying emergence more when the predator approached rapidly and directly. There was a significant interaction between directness and individual predator. Emergence times were similar for the two predators under low risk (indirect approach), but differed under high risk (direct approach). Experiments should use single predators or designs that control for differences among individual predators. All three risk factors affected emergence from refuge. Prey may be challenged by multiple risks and costs at a given time, and must be able to gauge at least the major ones with some degree of accuracy to make appropriate antipredatory decisions. Directness of approach, but neither approach speed nor individual predator, increased the likelihood that a lizard would emerge from refuge at a site other than the point where it entered the refuge. This suggests that lizards assessed directly approaching predators as more likely to have observed the entry point into refuge, and therefore as posing a greater threat upon emergence at the entry point.