Individual variation in antipredator behavior may be influenced by ecological factors, such as ambient temperature and predation pressure, and by intrinsic factors, such as physiological condition. We tested the hypothesis that both types of factors interact to induce a specific antipredator response in the treefrog, Scinax hiemalis. When disturbed by the threat of predation, individuals of this species exhibit either a passive response by feigning death or immobility, or an active escape response by jumping away. We examined the responses of 24 adult male S. hiemalis to simulated predation in the laboratory at 10, 15, and 20 C. In addition, responses from a single stimulus were compared with those from a series of stimuli. We determined physiological condition from measures of body length and mass, jumping performance, aerobic metabolism, and estimated energy reserves. Temperature had the most influence on antipredator behavior, with more frogs exhibiting passive responses at 10 C than at higher temperatures. If stimulated more than once, the proportion of active responses increased at all three temperatures. Larger individuals were more likely to exhibit an active response, but no mass-independent physiological variables were related to response type. These results suggest that frogs respond to both extrinsic and intrinsic factors that may affect their behavioral performance.
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Vol. 2002 • No. 4