THE INFLUENCE OF ADAPTIVE FORAGING DECISIONS ON SPATIAL HETEROGENEITY OF PARASITISM AND PARASITOID POPULATION EFFICIENCY

Incorporating adaptive behaviour in population models will lead to an understanding of phenomena at the population level based on natural selection. Parasitoids often have to decide whether or not to superparasitize (i.e. to parasitize hosts already containing one or more parasitoid larvae or eggs). Superparasitism has been shown to be adaptive according to an evolutionarily stable strategy model by Visser et al. In this paper, we study the consequences of adaptive superparasitism on (1) the heterogeneity of parasitism between patches and (2) the relationship between the efficiency (killing rate) of the parasitoid population and parasitoid density. To this end, a simple population model is constructed. In this model the parasitoid populations either adopt an evolutionarily stable strategy (ESS) with respect to superparasitism or specialize on unparasitized hosts (i.e. 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 higher in populations that superparasitize according to an ESS than in the specialist population. The killing rate, here used as a measure for efficiency, is consistently lower in the ESS populations, irrespective of the way parasitoids are distributed. Furthermore, 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. The results show that adaptive decisions of individuals with respect to superparasitism have an influence on processes at the population level in such way, that they potential contribute to stabilization of parasitoid-hosts interactions.