Abstract
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 for 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.
Highlights
Ecosystems experience considerable natural variability in environmental conditions, including disturbance events that influence the organization of biodiversity in space and time (Pickett et al 1989)
Ecological community responses to environmental change can be characterized by local α diversity, spatial β diversity and temporal β diversity, which collectively influence regional γ diversity (Tuomisto 2010)
distance to the closest perennial reach (DistPer) interacted with MonthSince (Fig. 6d) and DryMonth, indicating that increases in high Res community spatial β diversity with MonthSince and DryMonth were more pronounced at sites farther from perennial reaches
Summary
Ecosystems experience considerable natural variability in environmental conditions, including disturbance events that influence the organization of biodiversity in space and time (Pickett et al 1989). Rivers are dynamic ecosystems which experience natural hydrological variability, including flow cessation and drying in temporary rivers (Datry et al 2014a). Ecological community responses to environmental change can be characterized by local α diversity (e.g. taxonomic richness), spatial β diversity (variability in composition among sites) and temporal β diversity (site-specific compositional variability among times), which collectively influence regional γ diversity (Tuomisto 2010). Few field studies have explored biotic responses to natural hydrological variability along a spatial gradient of drying severity or considered timescales long enough to encompass droughts with different characteristics (Wood and Armitage 2004, Mathers et al 2019); even fewer characterize river-scale responses over long periods (Sarremejane et al 2018)
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