The evolution of fear-acquisition strategies under predation.

Fear is a taxonomically widespread behavioral response that functions to keep individuals out of danger. Empirical research has demonstrated that a diverse set of strategies are used in order to acquire a fear response across animals. Animals often use a mixed strategy: fear is acquired both innately and through learning. Despite the ubiquity of the fear response, and its established importance for shaping predator-prey interactions, little is known about why different fear acquisition strategies evolve or why mixed strategies appear common. Here, we model the evolution of fear acquisition (learning versus innate) under predation. We assume a tradeoff where individuals that learn fear are at higher risk from predators initially, but eventually obtain a lower risk as they survive predation attempts. We find that frequent predator encounters, predators that are not very dangerous, and effective learning favor the evolution of learned fear. Only pure strategies of fear acquisition evolve unless individuals suffer from either a cost to fear or, especially, a cost to learning, either of which can lead to the evolution of mixed strategies. Our results thus shed light onto the evolution of mixed fear acquisition strategies and open the door to further research on the evolution of fear acquisition.