Local and regional drivers influence how aquatic community diversity, resistance and resilience vary in response to drying

Disturbance events govern how the biodiversity of ecological communities
varies in both space and time. In freshwater ecosystems, there is evidence
that local and regional-scale drivers interact to influence ecological
responses to drying disturbances. However, most research provides temporal
snapshots at the local scale, whereas few studies encompass a gradient of
drying severity spanning multiple years. Using a dataset of rare
spatiotemporal extent and detail, we demonstrate how independent and
interacting local and regional-scale factors drive shifts in the α and β
diversities of communities in dynamic river ecosystems. We examined
aquatic invertebrate assemblage responses to hydrological variability (as
characterized by monthly observations of instream conditions) at 30 sites
over a 12-year period encompassing typical years and two severe drought
disturbances. Sites varied in their disturbance regimes and hydrological
connectivity at both local (i.e. site-specific) and regional (i.e. river
catchment) scales. Whereas α diversity was mainly influenced by local
factors including flow permanence and the temporal extent of ponded and
dry conditions, both temporal and spatial β diversities also responded to
regional-scale metrics such as the spatial extent of flow and hydrological
connectivity. We observed stronger local negative responses by taxa with
lower capacities to tolerate drying (i.e. resistance) and/or to recover
after flow resumes (i.e. resilience), whereas taxa with functional traits
promoting resilience made an increasing contribution to spatial β
diversity as hydrological connectivity declined. As droughts increase in
extent and severity across global regions, our findings highlight the
functional basis of taxonomic responses to disturbance and connectivity,
and thus advance understanding of how drying disturbances shape
biodiversity in river networks. Our identification of the role of regional
hydrological factors could inform catchment-scale management strategies
that support ecosystem resilience in a context of global change.