Behavioral and Life‐Historical Responses of Larval American Toads to an Odonate Predator

Abstract

This study examines the responses of larval American toads (Bufo americanus) to the non—lethal presence of an odonate predator (Anax junius). We performed a laboratory experiment where toad larvae were raised at four food rations crossed with the non—lethal presence (i.e., constrained Anax) and absence of the predator. Tadpoles facultatively responded by metamorphosing at smaller sizes in the presence of the predator and at lower food rations. Tadpoles also responded behaviorally to the presence of predators by reducing activity and altering spatial distribution. These latter reactions appeared to contribute to reduced growth rates in the presence of the predator at a given food level. We attempted to separate the effect of the predator on size at metamorphosis into components due to the effect on growth and to more direct effects of the predator, by comparing size at metamorphosis for individuals growing at the same rate in the presence and absence of the predator (i.e., at different food levels). Our data suggest that the metamorphic response may be mediated primarily through the behavioral effects on growth, which then affect size at metamorphosis. These results are consistent with theories of amphibian metamorphosis that predict that size at metamorphosis should depend on the relation between growth opportunities and risk of mortality in the larval and adult habitats. We discuss the importance of non—lethal effects of predators on prey performance, species interactions, and the evolution of prey defenses.