Data from: Seasonal and functional variation in the trophic base of intermittent Alpine streams

In high-altitude Alpine streams, seasonal cycles of snowmelt, glacial
melt, and rainfall drive variation in the availability of algal food
resources. Yet high-altitude streams also exhibit varying degrees of flow
intermittency, from solely winter-drying streams to others that dry
periodically throughout summer and autumn. These environmental drivers may
interact in different ways to determine the functional trophic base of
macroinvertebrates inhabiting high-altitude streams. Here, we estimated
the proportional contribution of autochthonous resources to the
assimilated diets of benthic macroinvertebrates in 26 headwater streams of
Val Roseg, a high Alpine glacial catchment, using stable isotope analysis
(δ13C and δ15N) of different macroinvertebrate families and their
potential food sources. We compared dietary estimates along a gradient of
flow intermittency and across 3 seasons (Alpine spring, summer and
autumn). Assimilation from autochthonous sources was highest for
collector-gatherers and filter feeders in spring, and for grazers in
summer. Grazers had higher estimated assimilation from autochthonous
sources in intermittent streams than in perennial streams, particularly in
summer, while collector-gatherers showed little effect of flow
intermittency on dietary estimates. However, responses were highly
taxon-specific, with different responses to variation in flow
intermittency and season across families within functional groups. Our
results suggest that frequent summer drying events represent trade-offs
between greater access to algal food resources and a higher risk of
desiccation, but that differing life-history and functional feeding traits
across macroinvertebrate taxa drive marked variation in the risks or
benefits associated with inhabitants of drying streams.