Effects of coexistence and predator experience on antipredatory responses of montane amphibian larvae towards native and introduced salmonids

Amphibian larvae are known to display defensive behavior in response to water borne chemical cues from aquatic predators that they recognize as a threat, either innately or via learning. Such potential for adaptive behavioral plasticity may increase population resilience in montane habitats, where many unique amphibian assemblages have suffered from salmonid introductions. Here we present data from three experiments assessing the effects of coexistence and long-term experience with native and introduced salmonid predators on behavioral responses of larvae from montane populations of the Iberian frog, Rana iberica. Further, we examine the potential costs imposed by natural and exotic predatory threats on larval growth and development. Larvae coexisting both syntopically and allotopically with salmonids reduced activity to avoid detectability. Interestingly, larval activity levels increased and larval responsiveness to predators decreased after long-term exposure to waterborne cues from predatory fish, likely due to habituation. Exposure to predator cues during development did not affect larval growth but altered the timing of metamorphosis by reducing larval period. Although growth is not directly compromised and individuals increase their short-term probabilities to survive with aquatic predators by reaching metamorphosis earlier, they might face the costs of predation-induced responses and developmental acceleration in later life stages.