Heightened prey responses in risky habitats: Predation pressure increases prey sensitivity to predation risk

Abstract

Previous studies have shown that prey living under intense consumer pressure possess stronger defenses against consumers than related species in habitats where consumer pressure is low. We tested whether prey sensitivity to risk would be heightened in habitats with elevated predation pressure and accordingly whether prey living in these areas would be more likely to initiate predator avoidance behaviors. Using the hard clam Mercenaria mercenaria as a model organism, we compared predation intensity on clams as well as their responses to predation risk from a population in Georgia to one in Maine, USA. Previous studies have shown that clams in Georgia react strongly to chemical cues from sympatric predators. In this study, we found that with the exception of starfish, clams from Maine did not react to their predators, and only responded when presented with cues from injured conspecifics. Predation was significantly greater in Georgia than in Maine, and clams from Georgia reacted more frequently and more intensely to risk than did those from Maine. The stronger responses from Georgia clams were observed when clams from both populations were assayed at the same level of risk (cue from injured conspecifics) and performed in the same environmental conditions. Our results suggest that prey sensitivity to chemical cues indicative of risk, and the intensity and frequency of responses to risk, may be related to local consumer pressure. Prey sensitivity to risk subsequently may display a geographical pattern, as predation is generally more intense in lower latitudes. © Inter-Research 2008.