The influence of land use, microhabitat and aquatic insect subsidies on predatory riparian arthropod distributions.

Agricultural land use effects to aquatic and riparian communities is complex and multifaceted, often resulting habitat degradation and biodiversity loss in riparian and instream ecosystems. This study correlatively evaluated predatory arthropod densities and species richness to abundance of potential prey (emerged aquatic insects and terrestrial dipterans), along an agricultural to forested land use gradient. Pearson’s correlation coefficient was used as an effect size to measure affinity to prey and the ratio of predator to prey was calculated to indicate potential consumption capacity of prey. Results revealed that gradients in land use and microhabitat condition, distance from the stream, and season were important explanatory factors. Positive correlations between predatory arthropods and aquatic insect abundance were more apparent compared to terrestrial dipteran abundance, suggesting an overall preference of aquatic prey. However, positive correlations between predatory arthropods and adult aquatic insect subsidies were strongest in microhabitats with characteristics associated with higher moisture (e.g. greater soil organic matter and shade), particularly with increasing agricultural land use. In September, there was indication of reduced confinement to microhabitats, likely as an effect of seasonal elevated precipitation. Overall results of this study suggest that a limited tolerance to desiccation in predatory arthropods increases spatial confinement with agricultural land use and ultimately restricts access to adult aquatic insect subsidies. The findings of this study have implications for the pathways that adult aquatic insect subsidies enter into riparian food webs with consequences that cascade across trophic levels and larger spatial scales.