Hungry predators render predator-avoidance behavior in tadpoles ineffective

Behavioral responses of prey to their predators can critically alter community dynamics. Whether or not a prey responds, clearly depends on the effectiveness of that response. The effectiveness on the other hand is predicted to depend on predator behavior. Actively searching predators can render the behavioral responses in their prey ineffective. Nevertheless, most studies investigating the optimal reaction of prey treated predators as immobile elements of the environment. I experimentally manipulated activity of poolfrog (Rana lessonae) tadpoles by keeping them at low and high food levels, and exposed them to three species of invertebrate predators (Aeshna cyanea, Anax imperator, and Dytiscus marginalis), whose activity also was manipulated through different food levels. Satiated, less active predators were more likely to kill hungry, more active tadpoles, but hungry predators killed hungry and satiated tadpoles about equally often. This result suggests that reducing their activity is a more effective strategy for tadpoles if the predators themselves are less active. On the other hand, against hungry, highly motivated predators, the behavioral avoidance strategies were essentially ineffective. Antipredator behavior is generally thought to stabilize the dynamics of predator-prey systems. The results presented here, however, suggest that the community dynamical consequences of antipredator behavior also critically depend on decisions made by predators.