Effect of urbanization on stream insect communities in adjacent headwater and downstream reaches

Abstract

Watershed urbanization causes decreased diversity in aquatic insect communities. Recent studies have focused on effects to aquatic life stages without consideration of impacts to adult terrestrial stages. Here, I review the potential impacts of urbanization on adult aquatic insects. The review suggests that urbanization may limit adult dispersal, limit taxa richness in urban headwaters, and increase similarity between communities in urban headwater and downstream reaches. Empirically, I compared communities in urban and rural headwater streams, compared community similarity between headwater and main-stem reaches in urban and rural watersheds, and examined longitudinal patterns of richness and community similarity along headwater streams in rural and urban watersheds. Diversity was lower for urban headwater communities. Similarity between headwater and main-stem communities was higher for urban watersheds. Longitudinal patterns of richness and similarity differed between urban and rural watersheds. These results support predictions that regional factors are partly controlling composition in urban headwater streams.