Predation and habitat isolation influence the community composition-area relationship in dytiscid beetles (Coleoptera: Dytiscidae)

Abstract

A major goal in ecology remains the understanding of patterns in diversity and distributions of species in natural communities. The species-area relationship is an important tool for investigating differences among communities, and may be also influenced by habitat isolation and dominant predator presence. In this two-year study, we evaluated the influences of habitat area, isolation and predation on community composition of dytiscids in two geographical regions dominated by different top predators (large predaceous dragonfly larvae or fish). Contrary to expectations, surface area, isolation and predator presence /absence alone did not significantly influence dytiscid species richness and total abundance, but in association with other environmental variables, such as submerged macrophyte growth forms. Components of habitat heterogeneity likely outweighed effects of area and predation regime on prey species diversity. However, differences in the set of abundant species were best explained by habitat surface area. Thus, in contrast to species diversity, gradients in community composition were not out-weighed by components of heterogeneity. In this study, predator presence was not correlated with habitat isolation. Instead, our results revealed that the effect of predator presence/absence on prey community composition and the resulting set of coexisting species may depend on habitat isolation. Within regions, the effect of large predaceous dragonfly larvae on species composition may depend on pond surface area, whereas the presence of fish influenced species composition alone and in association with area. We advocate that regional differences in environmental gradients be considered when community composition is evaluated.