OMNIVORY CREATES CHAOS IN SIMPLE FOOD WEB MODELS

Omnivory, defined as feeding on more than one trophic level, was considered rare in nature because of its destabilizing effect. However, recent elaborate studies of natural food webs have shown that omnivory is ubiquitous. It is well known that a simple food chain model of three trophic levels can exhibit chaos if the functional responses are nonlinear. We investigate a three-species Lotka-Volterra model of omnivory in which a predator and a prey share the same resource (i.e., intraguild predation). We demonstrate that intraguild predation sometimes destabilizes food webs and induces chaos, even if the functional responses are linear. The route to chaos is the familiar period-doubling cascade. We compare our results to previous work and discuss the mechanism by which omnivory induces chaos.