The influence of adaptive foraging decisions on spatial heterogeneity of parasitism and parasitoid population efficiency

Parasitoids often have to decide whether or not to parasitize hosts already containing one or more parasitoid larvae or egg. Superparasitism is adaptive according to an evolutionarily stable strategy (ESS) model. The authors study the consequences of adaptive superparasitism on the heterogeneity of parasitism between patches and the relationship between the efficiency (killing rate) of the parasitoid population and parasitoid density. Using a simple population model the parasitoid populations either adopt an ESS with respect to superparasitism or specialize on unparasitized hosts (ie they effectively are predators). The parasitoids are distributed among patches according to a negative binomial, Poisson or uniform distribution; the hosts are negative binomially distributed. In all cases, the heterogeneity of parasitism is high in populations that superparasitize according to an ESS than in the specialist population. The killing rate (a measure for efficiency) is consistently lower in the ESS populations, irrespective of the way parasitoids are distributed. There is no influence of the density of the parasitoids on the killing rate of the specialist population, while in the ESS population the killing rate decreases with increasing parasitoid density. Adaptive decision of individuals with respect to superparasitism thus have an influence on processes at the population level in such way, that they potentially contribute to stabilization of parasitoid-hosts interactions. -from Authors