Coexistence of Competing Parasitoid Species on a Host with a Variable Life Cycle

Abstract

Several special cases of a general model in which two parasitoid species attack different developmental stages of a single host species are presented. The inclusion of different mathematical forms of a maturation weighting function allows us to investigate the effect of several aspects of variation in immature stage durations on the outcome of competitition between the parasitoids. The two parasitoid species cannot coexist if the host developmental stages are fixed in duration. The outcome of competition depends in part on the relative duration of the two stages attacked by the parasitoid species. However, coexistence is possible if there is sufficient variation in the time that different host individuals remain in each stage. Distributed host developmental delays promote coexistence because they cause the host population to be composed of a mixture of host types with different relative egg versus larval stage durations. Each host type is thus largely available to only one of the parasitoid species.