Quantifying trophic niche spaces of small mammals using stable isotopes (δ¹⁵N and δ¹³C) at two scales across Alaska

Changing climate conditions are causing global distribution shifts, resulting in altered food webs and novel species assemblages in terrestrial systems. How diets of sympatric small mammals overlap and whether this may translate into competitive exclusion among new species interactions remains largely unknown. Monitoring niche overlap in changing arctic and boreal communities can assist in forecasting interspecific competition and species turnover. We quantified the isotopic niche spaces of small mammals, which may reflect dietary niche spaces, at study sites along two megatransects spanning Alaska. Field sampling resulted in the capture of 724 small mammals belonging to 12 species of rodent (10 Arvicolinae and 2 Sciuridae) and 6 species of shrew (genus Sorex L., 1758). We created dietary mixing models based on hair samples for four rodent species using stable isotope (δ 15 N and δ 13 C) analyses in R. We also modeled isotopic niche ellipses and quantified niche overlap among species at small and large scales. A varied combination of fungi and herbaceous plants composed the diets of most species. Fundamental niche spaces overlapped considerably between sympatric species statewide, but realized niche spaces were largely segregated at individual sites. We conclude that some degree of dietary plasticity served to partition niche spaces and minimize interspecific competition, allowing sympatric species to co-exist.