Understanding omnivory needs a behavioral perspective

While the importance of omnivory in community and food web ecology has received recent recognition, the behavioral basis of omnivory has not been thoroughly explored. Here we argue that understanding the basis of food mixing (i.e., eating different food types) and food selection behavior is central to understanding the causes and consequences of omnivory. Despite the existence of several alternative hypotheses, constraints imposed by nutrients are often assumed to explain the function of food mixing by omnivores and herbivores. However, few studies have actually addressed this issue through rigorous tests of multiple hypotheses. To illustrate the importance of non-nutritive factors, we marshal evidence for the roles of toxin dilution, parasite avoidance and resistance, and predation risk in food mixing and food selection by omnivores and polyphagous herbivores. Whether food mixing stabilizes population, community, and food web dynamics is likely to depend on the details of food selection and the spatial and temporal scales of food mixing.