Environmental conditions influence the frequency of prey responses to predation risk

Predators can strongly influence prey populations and the structure and function of communities by altering the foraging behavior and/or habitat selection of prey. For these nonlethal predator effects to occur, prey must be able to detect and respond to cues indicating predation risk. The ability of prey to detect and respond to predator signals likely varies with environmental conditions. To better understand how the environment can modify nonlethal predator effects by influencing the frequency of prey responses to predators, we examined how hydrodynamic conditions influence predator avoidance behavior in the dogwhelk Nucella lapillus, a carnivorous snail found on rocky intertidal shores. When confronted with predation risk, such as that signaled by water-borne chemical cues released by predatory green crabs, N. lapillus often reduce their movement and foraging activity. Using laboratory flumes, we explored how flow velocity and turbulence influenced responses by N. lapillus to predator risk cues. The influence of hydrodynamic conditions on predator avoidance behavior were nonlinear. N. lapillus responded to predators most frequently in intermediate flow velocities but less so in high and low velocities, suggesting that the effects of flow on predator avoidance behaviors are complex. Abiotic factors like flow can strongly influence the behavioral responses of intermediate consumers, which may propagate to other trophic levels via trait-mediated trophic cascades.