The hypothesis that predation presure permits increased niche overlap among prey species is sustained by analysis of a model in which a predator poplulation has been added to the three species "limiting similarity" model of MacArthur and Levins (1967). Also, it is predicted that there is a relation between the niche separation distances among prey and properties of the predators, and that if predation pressure is strong enough there is no limiting similarity among prey; i.e., complete niche overlap should be possible.