PREDATOR AVOIDANCE COSTS AND HABITUATION TO FISH CHEMICALS BY A STREAM ISOPOD

1. We examined whether long-term exposure to chemical cues of predator y longear sunfish (Lepomis megalottis) affected growth and rates of le af processing by the isopod, Lirceus fontinalis, an important facultat ive shredder in low-order streams in the eastern United States, and wh ether isopods habituated to sunfish chemicals. 2. Long-term (24 days) exposure to fish chemicals did not affect growth or the extent of leaf processing by isopods in the laboratory. Thus, chemical cues alone ma y not be important in triggering long-term predator avoidance behaviou rs that could potentially reduce fitness or affect community processes like litter breakdown. 3. Isopods exposed to fish chemicals for 3, 9 and 15 days were significantly more active than individuals unexposed to fish chemicals, when transferred to another environment with fish c hemicals. This result, coupled with results of the growth experiment, suggests that isopods habituate to fish chemical stimuli and that time to habituation is c. 3 days or less. Because fish chemicals can misle ad prey about predator presence, and hence be a non-threatening stimul us, they are probably important in eliciting only short-term antipreda tory behaviours by isopods.