Niche differentiation among small mammals of the Alexander Archipelago in southeastern Alaska

We compared isotopic niche widths of small mammals that co-occur across the Alexander Archipelago and adjacent mainland in southeastern Alaska to test the prediction that dietary niche widths will be greater for individuals living in communities with fewer potential competitors and predators. We quantified the carbon (delta C-13) and nitrogen (delta N-15) isotopic niche widths of 2 insectivorous shrews (Sorex cinereus and S. monticola), 3 primarily herbivorous rodents (Microtus longicaudus, M. oeconomus, and M. pennsylvanicus), and 1 omnivorous rodent (Peromyscus keeni) and combined these data with information provided by natural history accounts. We sampled islands that varied with respect to size and species richness to compare with localities on the adjacent mainland, where species richness is greatest. Consistent with our predictions, isotopic niche widths were significantly greater on islands relative to mainland localities. Our findings can help guide management strategies within this archipelago through increased understanding of how key community-level interactions vary across localities within this complex landscape.