CHEMICALLY MEDIATED AVOIDANCE OF A PREDATORY ODONATE (ANAX-JUNIUS) BYAMERICAN TOAD (BUFO-AMERICANUS) AND WOOD FROG (RANA-SYLVATICA) TADPOLES

Predators can have significant nonlethal effects on prey by modifying prey behaviour through chemically mediated interactions. We examined b ehavioural responses of wood frog (Rana sylvatica) and American toad ( Bufo americanus) tadpoles to both direct and indirect chemical signals associated with a predatory odonate (Anax junius). In laboratory tria ls, tadpoles of both species responded strongly to water conditioned w ith Anax nymphs by decreasing foraging rates, becoming immobile, and m oving away from the stimulus. The responses to water conditioned with starved Anax versus Anax that fed on conspecific tadpoles did not diff er significantly; these results suggest that tadpoles rely primarily o n direct signals to detect odonates. Rana did not respond to water con ditioned with conspecific tissue extracts, while Bufo responded with b ehaviours that were indistinguishable from those of tadpoles exposed t o Anax-chemicals. In a field experiment, the responses of R. sylvatica tadpoles to Anax chemicals were similar to those of tadpoles observed in the laboratory. Collectively, our data indicate that tadpoles of b oth species use chemical cues to assess predation risk from other comm unity members. Tadpoles can selectively distinguish members who pose a threat, and only evacuate food patches or reduce foraging rates when in danger. These behaviours appear to be adaptive and are consistent w ith the predictions of optimality theory.