Predator avoidance strategies of the crayfish Orconectes virilis.

Abstract

A behavioral field experiment tested for differences between the alarm and disturbance responses of the crayfish Orconectes virilis, and compared these responses to those of Orconectes propinquus, a less chemically sensitive sympatric species. Despite the lack of a significant difference between the two types of response and a control, there are differences between the disturbance and alarm responses of O. virilis. The results indicate that, since alarm substance is a more specific cue of predation risk than disturbance substance, an aversive alarm response is a more effective predator avoidance strategy than an aversive disturbance response. As expected, O. propinquus shows no response to the experimental treatments. In addition, the results demonstrate that O. virilis individuals follow a lunar cycle of activity, with the greatest activity near new moon, and the least near the full moon. The cyclic change in activity is probably an additional predator avoidance strategy, protecting individuals from being captured by visually hunting predators on particularly bright nights. Although the results were suggestive of a lunar cycle in the activity of O. propinquus, insufficient data was available to test for this possibility.