The sensory ecology of nonconsumptive predator effects.

Nonconsumptive effects (NCEs) have been shown to occur in numerous systems and are regarded as important mechanisms by which predation structures natural communities. Sensory ecology-that is, the processes governing the production, propagation, and masking of cues by ambient noise-provides insights into the strength of NCEs as functions of the environment and modes of information transfer. We discuss how properties of predators are used by prey to encode threat, how the environment affects cue propagation, and the role of single sensory processes versus multimodal sensory processes. We discuss why the present body of literature documents the potential for strong NCEs but does not allow us to easily determine how this potential is expressed in nature or what factors or environments produce strong versus weak NCEs. Many of these difficulties stem from a body of literature in which certain sensory environments and modalities may be disproportionately represented and in which experimental methodologies are designed to show the existence of NCEs. We present a general framework for examining NCEs to identify the factors controlling the number of prey that respond to predator cues and discuss how the properties of predators, prey, and the environment may determine prey perceptive range and the duration and frequency of cue production. We suggest how understanding these relationships provides a schema for determining where, when, why, and how NCEs are important in producing direct and cascading effects in natural communities.