Intensive agriculture alters the biomass size spectrum and body-mass of benthic insects: evidence from a reciprocal transfer experiment

Abstract

The aim of this study was to test the effects of agricultural land use on benthic insect population body-mass and community biomass size spectrum. Agricultural land use effects were assessed by conducting a reciprocal transfer experiment between two stream reaches exposed to differing intensities of row crop and livestock agricultural activity representing best attainable and highly developed agricultural land use scenarios. We found that transferred insect communities showed no change in richness, abundance, distribution or biomass, indicating that exposure to increased agricultural intensity did not have selective lethal effects on transferred benthic insect communities. However, populations of Ephemerellidae and Hydropsyche demonstrated an increase and decrease, respectively, in body-mass following the transfer to the best attainable agriculture site. Furthermore, the community biomass size spectrum at the best attainable agriculture site contained large, predatory insects not found at the intensive agriculture site. Our findings suggest that taxon-specific body-mass and biomass size spectra have the potential to detect environmental effects prior to long-term community changes. Further research is needed to explore the mechanisms by which changes in the biomass size spectrum link agricultural intensity to shifts in benthic insect community structure.