Riparian hunting spiders do not rely on aquatic subsidies from intermittent alpine streams

Drying in alpine streams might decrease aquatic-terrestrial trophic linkages by reducing terrestrial predation on aquatic prey. We tested this hypothesis by investigating whether a common riparian predator (hunting spiders) in alpine environments assimilated a lower proportion of aquatic prey with increasing stream intermittency. We used high temporal-resolution data from electrical resistance sensors to map patterns of naturally-occurring flow intermittency across 30 headwater streams of Val Roseg, a glacierized catchment in the Swiss Alps. We collected riparian hunting spiders, as well as potential terrestrial and aquatic macroinvertebrate prey, from streams and their associated riparian zones across two seasons (Alpine spring and summer). We estimated aquatic contributions to spider diets (pA) using (i) a gradient approach with aquatic invertebrate and spider carbon stable isotope ratio values (δ13C), and (ii) Bayesian carbon and nitrogen (δ15N) isotope mixing models. Spider pA from ...