Threat-sensitive predator avoidance by larval pacific treefrogs (Amphibia,Hylidae)

According to the threat-sensitive predator avoidance hypothesis, the intens ity of a prey animal's antipredator response should reflect its vulnerabili ty to a specific predator. In laboratory experiments, we observed the inten sity of antipredator responses of Pacific treefrog (Hyla regilla) tadpoles to stimuli from caged larval northwestern salamander (Ambystoma gracile) pr edators. We varied the sizes of the tadpoles relative to the salamanders in an attempt to create differences in vulnerability of tadpoles to the salam ander predators. After documenting the response of the tadpoles to the cage d predator, we tested the tadpole's vulnerability to the predator by releas ing the tadpole with the predator. We observed that as the relative size of the tadpoles to the caged salamanders increased, the antipredator response of the tadpoles decreased. These changes in behaviour closely mirrored cha nges in actual vulnerability to the predator. Our results provide experimen tal support for the threat-sensitive predator avoidance hypothesis.