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

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.