Habitat fragmentation and the stability of predator–prey interactions

Abstract

Mathematical models^1–3, field observations^4,5, and laboratory studies⁶ all suggest that habitat patchiness (or 'fragmentation') profoundly affects species interactions. One especially widely cited idea is that patchiness stabilizes predator–prey dynamics^7,8. I performed the first test of this idea in a natural community by experimentally manipulating the degree of patchiness in goldenrod fields that were the setting for a predator–prey interaction between ladybird beetles and aphids. Contrary to conventional wisdom, I found that increasing patchiness led to more frequent local explosions of aphid populations and thus less stable dynamics. These results can be understood by examining the effects of patchiness on the searching and aggregation behaviour of ladybird predators. It appears that the effects of habitat fragmentation depend on the specific behaviour of the organisms using the habitats. Thus, instead of making robust generalizations about habitat fragmentation (such as "patchiness is stabilizing") we should seek predictions that are based on the details of an organism's dispersal behaviour and demography⁹.