Patch edges and insect populations

Abstract

Responses of insect populations may be related to patch size and patch edge responses, but it is not clear how to identify these rapidly. We used a random-walk model to identify three qualitative responses to edges: no edge effect (the null model), reflecting edges and absorbing edges. Interestingly, no edge effect meant that abundance was lower at edges than in the center of patches, and reflecting edges have similar abundance at edges and centers. We then characterized several insect species' response within maize plots to patch edges and patch size, using a simple, quick, qualitative experiment. Coleomegilla maculata and Trichogramma spp. were the only organisms that responded to patch size and edges as patch theory and the null edge model would predict. Ostrinia nubilalis larvae and possibly Rhopalosiphum maidis and eggs of Chrysopa spp. responded to patch size and edges as predicted by an attracting edge model. Estimation of predation rates suggested that the spatial distribution of these species might be determined by predators. Edge effects or the lack thereof relative to patch size may be rapidly determined for arthropod species, which could lead to understanding the mechanism(s) underlying these effects. This information may be useful in reaction diffusion models through a scaling-up approach to predict population structure of species among patches in a landscape.