A general version of optimal foraging theory: The effect of simultaneous encounters

Optimal foraging theory is extended so as to treat cases where a choice between several options is required. A new version of optimal foraging theory is derived under this assumption of simultaneous encounters of prey species and proved by using a set-theoretic approach. On the basis of this new version, it is demonstrated that, in general, no unique ranking of food types can be specified only from knowledge of the intrinsic properties of the food types. It is demonstrated that a food type may become less frequent in the diet as a result of becoming more abundant in the environment; that an increase in the abundance of a food type represented in the diet may have the effect that new food types enter the diet; and that an increase in the overall food abundance may imply that new types are included and/or old ones are excluded.