The responses of prey fish to temporal variation in predation risk: sensory habituation or risk assessment?

Predation is an important selection pressure acting on prey behavior. Although numerous studies have shown that when predation risk is high, prey tend to increase vigilance and reduce foraging effort, until recently, few studies have looked at how temporal patterns of risk influence the trade-off between foraging and antipredator behavior. The risk allocation hypothesis predicts that prey should respond strongly to predators that are usually absent, as they can meet their energy demands during safe periods. In contrast, if predators are almost always present, prey need to forage actively even though predators are present, a counter-intuitive prediction for many behavioral ecologists. This decrease in antipredator behavior on increasing exposure to risk has thus far been attributed to sensory habituation. Using cichlids, we show that sensory habituation is likely not the proximate explanation for the reduction in antipredator behaviors in this system. Such responses may rather be the result of adaptive decision making.