Climate change is expected to profoundly affect freshwater ecosystems by reshaping the distribution and prevalence of aquatic taxa, with cascading consequences for community structure and ecosystem function. One increasingly important impact of climate change is rising stream intermittency, which alters hydrologic regimes and imposes strong environmental filters on stream communities. To evaluate how projected increases in temperature and changes in precipitation may influence stream macroinvertebrates under increasing intermittency, we applied ensemble species distribution models to data from more than 1,000 stream sites across Washington State, with a focus on functional traits related to flow sensitivity and disturbance tolerance.
We compared downscaled CMIP6 climate projections for 2081–2100 under four greenhouse gas emission scenarios with historical climate conditions for 391 macroinvertebrate taxa. Analyses emphasized functional traits expected to respond predictably to intermittency, including voltinism, rheophily, and functional feeding groups. Our objectives were to (1) identify the bioclimatic variables to which macroinvertebrate taxa are most sensitive and (2) quantify projected changes in the prevalence and spatial distribution of functional trait modalities. We hypothesized declines in semi-voltine taxa and increases in multivoltine taxa, along with losses of erosional taxa and increased prevalence of depositional taxa.
Annual precipitation emerged as the most influential predictor for the majority of taxa, followed by annual mean temperature and precipitation seasonality. Projections indicated increases in the prevalence of multivoltine taxa and taxa associated with depositional habitats across emission scenarios, with stronger responses under higher carbon scenarios. In contrast, semi-voltine taxa and taxa associated with erosional habitats consistently declined in prevalence. Functional feeding groups also exhibited pronounced shifts, with declines in shredders and collector–filterers and increases in herbivores and parasites across scenarios.
Together, these results suggest that increasing stream intermittency may substantially restructure stream communities and alter ecosystem function by favoring fast-reproducing taxa and shifting the prevalence of functional feeding groups.