Ecological drift drives anthropogenic impacts on multiple facets of aquatic insect diversity

Abstract

Human disturbance is a major threat to natural ecosystems globally. However, how disturbances alter the interplay of deterministic and stochastic processes underlying community structure and diversity remains to be clarified, as evidence from natural systems is particularly lacking. Here, we investigated how the taxonomic, functional, and phylogenetic α and β diversity of aquatic insects respond to a gradient of cumulative human disturbances in a large subtropical river network. We then evaluated the impacts of individual stressors measured at local, riparian, and catchment scales on these multifaceted diversity dimensions. Finally, we used a null model approach to test how human impacts modulate the relative role of ecological drift, selection, and dispersal in community organization. Human impacts differentially affected α diversity measures, with species richness and mean pairwise distance indices (MPD) decreasing, while mean nearest‐taxon distance indices (MNTD) increased from near‐pristine to highly impacted sites. Human impacts were also associated with increased β diversity, leading to biotic differentiation. Catchment land uses overrode the effects of riparian and local instream stressors in regulating insect diversity. The assembly of insect communities was primarily driven by ecological drift, with heterogeneous selection playing a secondary role. Human impacts mediated the balance between deterministic and stochastic processes by disrupting species interactions and promoting ecological drift. Our study demonstrates that the role of ecological drift in community assembly should not be overlooked, especially given that many biological communities are shrinking in size due to escalating environmental pressures during the Anthropocene.