Interspecific interactions reflect the cumulative consequences of individual behavioral acts. The foraging decisions made by predators influence the way in which predation shapes the structure of prey communities. Alternative prey species co-occurring in a patch embedded in a matrix of many similar patches may interact through a shared mobile predator in two distinct ways. First, the functional response by an individual predator foraging in the patch to one prey species may be affected by the density of a second prey species in the patch (e.g., any time spent handling one prey reduces the time available for capturing other prey). Second, the presence of a second prey species may alter the propensity of predators to aggregate or remain in a given patch. We argue that this aggregative numerical response can in many circumstances generate -, - interactions (apparent competition) between prey species that otherwise would not interact. This is most likely if predators use a simple optimality criterion for prey...