INDIVIDUAL BEHAVIOR AND HIGHER-ORDER SPECIES INTERACTIONS

In this article I address the manner in which ecological and developmental factors shape behaviors and the consequences of these behaviors to species interactions. An important potential consequence of adaptive behavioral responses is higher-order interactions among species (e.g., in which the presence of a third species qualitatively alters the nature of the interaction between two other species). To illustrate this potential, I examine two broad classes of adaptive behavioral responses, choice of activity level and of habitat. I review evidence that suggests that in many organisms these behaviors are mediated by trade-offs between resource acquisition and mortality risk. This trade-off provides a conceptual foundation on which to predict individual behavior, and since the trade-off changes with size, marked behavioral allometries may occur over an individual's ontogeny. I present evidence that these sorts of behavioral responses create strong higher-order interactions. I argue that theory at the individual behavioral level affords the opportunity for a rich interaction between theory at the individual and population levels by providing a mechanistic basis for species interaction theory. Because behavioral responses are occurring on the same time scale as direct effects, ecologists will need explicitly to include adaptive behavioral mechanisms in the theory to understand species interactions in many systems. Finally, I discuss how behavioral allometries may contribute to selection on features of the life cycle.