Climate-driven hydrological variability determines inter-annual changes in stream invertebrate community assembly

Although flow regime is one of the major drivers of riverine communities, not much is known about how inter-annual variability and extremes of flow influence community assembly mechanisms. We used data on benthic macroinvertebrates and modelled flow regimes in 23 near-pristine boreal streams to assess how community assembly mechanisms and species occupancy varied in response to inter-annual variability in flow conditions across 11 successive years encompassing extreme (both low and high) flow events. A null model approach was used to test whether deterministic or stochastic processes dominated community assembly and how much regional (among-stream) flow variability contributed to community variability (β-diversity). Mean daily flow and the greatest rate of flow rise were the strongest flow-related descriptors of invertebrate community composition. Communities were differentially assembled depending on the direction of change in flow magnitude: in high-flow years, communities were more s...