Differential habitat use and antipredator response of juvenile roach (Rutilus rutilus) to olfactory and visual cues from multiple predators.

The indirect, behavioral effects of predation and predator-predator interactions can significantly alter the trophic ecology of many communities. In numerous instances, the strength of these effects may be determined by the ability of prey to identify predation risk through predator-specific cues and respond accordingly to avoid capture. We exposed juvenile roach (Rutilus rutilus), a common forage fish in many brackish and freshwater environments, to vision and/or olfactory cues from two predators with different hunting methods: northern pike (Esox lucius, an ambush predator) and European perch (Perca fluviatilis, a roving predator). Our results demonstrated that responses of roach to perceived risk (as evidenced by their selection of structured or open-water habitats) were highly dependent on cue type and predator identity. For instance, roach responded to olfactory cues of pike by entering open-water habitat, but entered structured habitat when presented with a vision cue of this predator. Opposite responses were elicited from roach for both olfactory and visual cues of perch. Interestingly, roach defaulted to selection of structured habitat when presented with vision + olfaction cues of either predator. Moreover, when presented individual cues of both predators together, roach responded by choosing open-water habitat. Upon being presented with vision + olfaction cues of both predators, however, roach strongly favored structured habitat. Differences in habitat selection of roach were likely in response to the alternative foraging strategies of the two predators, and suggest that prey species may not always use structured habitats as protection. This appears particularly true when a threat is perceived, but cannot immediately be located. These results provide insight to the complex and variable nature by which prey respond to various cues and predators, and offer a mechanistic guide for how behaviorally mediated and predator-predator interactions act as structuring processes in aquatic systems.