Predator size and distance to edge: is bigger better?

I investigated the use of edge by soil arthropods by testing whether mesoar thropod predators were closer to edge than expected and whether large preda tors were closer to edge than small predators. The experimental design cons isted of 120 boxes, each covering 200 cm(2) of soil, that were randomly dis tributed within a 0.13-km(2) aspen stand located in the Canadian prairie re gion. Each 2-kg box depressed the leaf litter, creating a microhabitat isla nd for soil arthropods consisting of 61 cm of edge. During 20 weekly survey s from May to September in 1997 and 1998, numbers and distribution of arthr opods located immediately beneath the boxes were recorded. Mesoarthropod pr edators were found closer to edge than expected. Centipedes, beetle larvae, and predatory mites (Acari) were found at intermediate distances to edge, whereas beetles, ants, adult flies, bugs, and spiders were distributed adja cent to edge. Generally, larger mesoarthropod predators were found closer t o edge than smaller individuals, within each taxonomic group. Collembola, t he major mesofauna prey, were distributed randomly with respect to edge dur ing wet periods of high density. During the subsequent dry periods, reduced densities of Collembola occurred and distribution became skewed, with grea ter numbers in interior areas and reduced densities near edges. Temperature and moisture under the boxes did not vary with distance to edge, although the microclimate was cooler and more humid under the experimental boxes rel ative to beyond the boxes. These results support the hypotheses that mesoar thropod predators forage along box edges (i.e., linear corridors) and that larger individuals may gain access to edge owing to their larger size, alth ough alternative explanations are possible, depending on the particular tax onomic group.