Data from: 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
similar than expected by chance, while at low flows they tended to be more
dissimilar than expected. Beta-diversity of macroinvertebrate communities
was related to among-stream flow variability only at high flows. Common
species correlated strongly with flow variability and contributed most to
variation in β-diversity, suggesting that changes in assembly mechanisms
are mainly driven by common species. While homogenization of communities
in high-flow years reflected increased species occupancies and
environmental sorting, increased turnover during low flows likely resulted
from stochastic extinctions and dispersal limitation. Our findings suggest
that extreme hydrological events exert a strong control over stream
invertebrate community assembly, and their effect may be even more
profound in the future as high and low-flow spells are expected to occur
more frequently, not allowing time for communities to recover.