Stable Isotopes and Radiocarbon Assess Variable Importance of Plants and Fungi in Diets of Arctic Ground Squirrels

ABSTRACT Arctic ground squirrels (Urocitellus parryii) rely primarily on dietary protein derived from plants to fuel gluconeogenesis during hibernation, yet fungal sporocarps may be an important, yet overlooked, protein source. Fungivory levels depend on sporocarp productivity, which varies with the dominant plant species and is higher on acidic than on non-acidic soils. To test whether these factors altered fungal consumption, we used stable isotopes to investigate arctic ground squirrel diets at two sites in northern Alaska, Toolik (primarily moist acidic tundra) and Atigun (primarily moist non-acidic tundra). Radiocarbon estimates can also indicate fungivory levels because ectomycorrhizal fungi assimilate soil-derived organic nitrogen whose 14C levels are higher than current photosynthesis. We measured radiocarbon in hair and δ13C and δ15N in hair, feces, ectomycorrhizal sporocarps, graminoids, and dicots. Feces were higher in δ13C and δ15N at Toolik than at Atigun, and fecal δ15N increased in August a...