78.1 Friday, Jan. 6 Fine tuning anti-predator responses: are the costs of inducible predator defences proportional to the magnitude of the responses? HEINIGER, J*; VAN UITREGT, V; WILSON, R S; University of Queensland; University of Queensland; University of Queensland email@example.com
The threat-sensitive predator avoidance hypothesis predicts the magnitude of inducible defensive responses should reflect the degree of threat. This allows organisms to maximise the effectiveness of the defence whilst minimising the associated costs. Although we know prey can fine-tune their responses to the degree of predation risk, it is unclear if the magnitude of threat-sensitive defensive responses relate to their associated costs. We tested this assertion by examining the effects of increases in perceived predation risk on the expression of inducible defences and their associated costs in larvae of the cane toad, Bufo marinus. We reared larvae in varying concentrations of predation cue and quantified their growth, morphology and development, as well as metamorphic size, locomotor performance and oxygen consumption. We predicted the magnitude of inducible defensive responses of larvae would be proportional to the associated costs experienced by the metamorphs. Larvae responded to increases in perceived predation risk in a threat sensitive manner by gradually decreasing their activity. As a consequence, individuals metamorphosed later, smaller and with reduced endurance. Although no differences in maximum jumping distance were detected among treatments, the longer relative hind limbs of metamorphs that experienced high predation cues allowed them to jump further for their overall body size. In support of our predictions, we found the costs of producing an inducible defensive response were proportional to the magnitude of the response. Thus, our data support the hypothesis that prey can fine tune their anti-predator responses to the intensity of threat, allowing prey to balance the costs experienced against the benefits to predator avoidance.