Influence of environmental conditions on patch exploitation strategies of parasitoids

In patchy environments, patch-leaving decision rules are a key component of the foraging behavior of parasitoids that have to share their searching time between the different host patches to optimize the number of ovipositions. It has been experimentally shown that one of the proximate cues involved in patch-leaving decision is the number of ovipositions performed by the parasitoid while in the patch. Ovipositions can have either a decremental or an incremental effect on the patch residence time depending on parasitoid species. Previous theoretical studies have suggested that environmental conditions and the ability of parasitoids to reliably estimate the number of available hosts on a patch when entering it should influence how patch departure depends on ovipositions. We developed an individual-based model to test a large variety of patch-leaving decision rules in different environmental conditions. This model includes a more realistic representation of individual acquisition of information than previous theoretical work. In accordance with previous results, we show that the best use of information depends on environmental conditions. Moreover, we identify the environmental factors that have a decisive influence on the most appropriate type of rule (incremental or decremental). Decremental mechanisms are most efficient only in restricted conditions characterized by a large number of patches and few parasitoids. The sensitivity of decision rules to frequency-dependent processes was tested by numerical invasibility experiments. Rare mutants using any alternative rule never outperform populations using a high-performance rule. Incremental rules seem to be more sensitive than decremental ones to frequency-dependent processes. Copyright 2007, Oxford University Press.