The Effects of Habitat Size and Productivity on Food Web Structure in Small Aquatic Microcosms

Abstract

We discuss two mechanisms by which habitat size could affect food web structure: productive space and spatial effects on the persistence of unstable interactions. We assembled communities of bacteria, protozoa, rotifers, microcrustacea and Hydra in laboratory microcosms, and independently manipulated habitat size and total energy input, in order to distinguish between these mechanisms. After 163 d, larger habitats supported food webs with more species, more links per species and longer food chains, even in the absence of differences in total energy input. There were no significant differences in food web structure between energy treatments. Some species' relative abundances were affected by habitat size or energy, but there was no consistent overall pattern of responses. These results do not support the productive space hypothesis, but suggest that spatial effects on the persistence of unstable food webs may be important, although differences in disturbance between different sizes of microcosm may also have been a factor.