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Data from: Experimentally induced low flows indicate climate change may shrink trophic niches of mountain-stream predators

Cowell, Ashley1; Leathers, Kyle1; de Mendoza, Guillermo12; Dwyer, Grace1; Herbst, David3; Ruhí, Albert1

Research facility: Sierra Nevada Aquatic Research Laboratory
Published Jul 23, 2025 on Dryad. https://doi.org/10.5061/dryad.jdfn2z3pj

Data files

Abstract

Climate change is projected to decrease snowpack and advance snowmelt in mountain ranges globally—including in California’s Sierra Nevada, where streamflow in snow-dominated rivers is expected to peak up to 2 mo earlier and remain in baseflow conditions for extended periods of time. Predators may be particularly sensitive to low flows, owing to their larger body sizes, higher metabolic demands, and longer lifespans. Experimental manipulations can improve understanding of how these predators, and the food webs they are embedded in, are likely to respond to future snow droughts. We experimentally examined how the trophic ecology of predatory macroinvertebrates responds to the extended low flows expected under climate change. We manipulated flow regimes in outdoor, large-scale artificial streams in the Sierra Nevada to produce a current flow regime and 2 future regimes that advanced low-flow conditions by 3 and 6 wk, respectively. We performed stable isotope analysis on the macroinvertebrate community, focusing on 3 predatory taxa (Perlidae stoneflies [Plecoptera], Rhyacophila caddisflies [Trichoptera], and Turbellaria flatworms), as well as nonpredatory invertebrates (n = 310 samples across 8 taxa). We examined the isotopic signals (δ15N and δ13C) of the predators and quantified how their isotopic niche areas, trophic positions, and energy sources varied seasonally and following low-flow treatments. We also performed gut content analysis of Perlidae, and we compared the predator assemblage response to that of other feeding groups. We found that low flows compressed the trophic niches of predatory taxa, with variable responses across taxa and treatments. Perlidae stoneflies had fewer prey items in their guts under extended low flows. Lastly, only the predator feeding group was severely affected by the most extreme low-flow treatment (62% niche compression). Our experiment suggests that climate-driven low flows will likely shift invertebrate predators’ diets, and thus foodweb structure, in Sierra Nevada streams. However, response diversity among taxa illustrates the need to preserve diverse alpine stream assemblages in the face of future hydroclimates.