Avoidance response of juvenile pacific treefrogs to chemical cues of introduced predatory bullfrogs

Bullfrogs (Rana catesbeiana), native to eastern North America, were introdu ced into Oregon in the 1930's. Bullfrogs are highly efficient predators tha t are known to eat a variety of prey including other amphibians. In laborat ory experiments, we investigated whether juvenile Pacific treefrogs (Hyla r egilla) recognize adult bullfrogs as a predatory threat. The ability of pre y animals to acquire recognition of an introduced predator has important im plications for survival of the prey. We found that treefrogs from a populat ion that co-occurred with bullfrogs showed a strong avoidance of chemical c ues of bullfrogs. In contrast, treefrogs from a population that did not co- occur with bullfrogs, did not respond to the bullfrog cues. Additional expe riments showed that both populations of treefrogs use chemical cues to medi ate predation risk. Treefrogs from both populations avoided chemical alarm cues from injured conspecifics.