Investigating Impacts of Landscape Development on Stream Fish and Insect Dispersal

Land use/cover at the catchment scale is an important predictor of stream geomorphology and water chemistry, and, in turn, fish and insect assemblages. However, land use in the catchment does not fully capture areas that fishes and insects use for dispersal, a potentially important mechanism for biotic assemblage alteration in urbanizing streams. Our objective was to evaluate the relative importance for land use/cover quantified at different spatial scales at affecting fish and insect richness, diversity, and composition in Massachusetts streams.  We assessed land use/cover based on the drainage area, a 500-m radius, and the stream corridor 1 km upstream and downstream of sites. Using a model selection framework, we found that catchment characteristics (i.e., within the drainage area) were consistently strong predictors of fish and insect richness and diversity. Land cover along the stream corridor was an important predictor of fish richness and diversity while land use/cover in the radius was not. In contrast, percent developed land within a radius around the site was an important predictor for insects while characteristics of the corridor were not. These results highlight the importance of in-stream dispersal barriers for fish and overland dispersal for insects.