Data from: Drought intensification drives turnover of structure and function in stream invertebrate communities

Climatic extremes are becoming more frequent and intense across much of
the globe, potentially transforming the biodiversity and functioning of
affected ecosystems. In freshwaters, hydrological extremes such as drought
can regulate beta diversity, acting as powerful environmental filters to
dictate the complement of species and functional traits found at local and
landscape scales. New methods that enable beta diversity and its
functional equivalent to be partitioned into turnover (replacement of
species/functions) and nestedness-resultant (gain/loss of
species/functions) components may offer novel insights into the parallel
impacts of drought on ecosystem structure and function. Using a series of
artificial channels (mesocosms) designed to mimic perennial headwater
streams, we experimentally manipulated streamflows to simulate a gradient
of drought intensity. We then modelled taxonomic and functional turnover
and nestedness of macroinvertebrate communities along this gradient,
validating direct gradient approaches (bootstrapping, Mantel tests)
against null models of nestedness. Drought intensification produced
significant environmental distance decay trends (i.e. communities became
increasingly taxonomically and functionally dissimilar the more
differentially disturbed by drought they were). Taxonomic distance decay
was primarily driven by turnover, while the functional trend reflected a
combination of richness differences and turnover at different points along
the gradient. Taxonomic and functional distance decay slopes were not
significantly different, implying that communities were functionally
vulnerable to drying. The increased frequency and intensity of droughts
predicted under most climate change scenarios could thus profoundly modify
not only the structure of running water invertebrate communities, but also
the ecosystem functions they underpin.