When to come out from a refuge: risk-sensitive and state-dependent decisions in an alpine lizard

Prey often respond to predator presence by increasing theiruse of refuges. However, unfavorable thermal conditions in refugesmight entail physiological costs for an ectothermic prey. Thus,the decision of when to come out from a refuge should be optimizedby considering the expected fitness effects of diminution ofpredation risk with time, but also by considering the cost of theloss of time spent at optimal body temperature maximizing physiological functions.The model of Ydenberg and Dill describes the trade-off betweenrisk and cost for a prey fleeing to a refuge. We present a specialcase of this model to predict how emergence time from the refugein lizards or other ectotherms should vary as a function ofrisk of predation and thermal costs of refuge use. The analysesof the variation in emergence time from a refuge of Lacertamonticola lizards in the field under two different predation risklevels supported the predictions of the model. As predicted,time spent in the refuge was longer when the threat of the initialattack had been higher, and therefore the subsequent diminutionof risk was slower, but only when lizards emerged at the sameplace where they hid. When initial body temperature was high,some lizards decreased emergence time by emerging from a differentplace. In addition, the effects of thermal costs were more relevant inthe high-risk situation. Time spent in the refuge under highrisk increased when thermal conditions of the refuge were moresimilar to thermal conditions outside (i.e., physiological costsof refuge use were lower). We conclude that optimization ofrefuge-use strategies might help lizards cope with changes in predationrisk without incurring excessive physiological costs.