Frequency of encounter with risk and the tradeoff between pursuit and antipredator behaviors in crayfish: A test of the risk allocation hypothesis

Prey animals encountering multiple stimuli must often make behavioral tradeoffs. Many environmental cues may influence the tradeoff observed, but recent theoretical work suggests that temporal variation in risk should influence how prey animals behave during any given period of risk. As time spent under risk of predation increases, prey animals will increase their allocation of foraging during periods of risk. This model is known as the risk allocation hypothesis (RAH) (Lima & Bednekoff 1999). We tested the RAH using the crayfish Orconectes virilis . We selected two frequency regimes (exposure to risk every 6 or 12 h) and three cues suggestive of increasing risk (water, snapping turtle cue, and conspecific alarm cue). Test animals were exposed to one of the six frequency x risk combinations for 24 h, followed immediately by the simultaneous introduction of a food and a risk cue. Three behaviors (burrow use, non-ambulatory motion, and locomotion) were then recorded for 5 min. Responses were significantly influenced by the interaction of risk and frequency. Further analysis indicated that responses were not consistently influenced by frequency alone. While our results do not support the predictions of the RAH for our frequency regimes, qualitative comparison with an earlier, similar study (Hazlett 1999) suggests that risk allocation is occurring in this system. We recommend that frequency of encounter with risk be considered in future studies. Ignoring temporal variation may lead to over- or underestimation of the subject's natural responses.