Why is small mammal diversity higher in riparian areas than in uplands?

Abstract

Riparian areas are valued in arid regions for supporting wildlife diversity. We examined relationships between small mammal diversity and riparian areas and mechanisms facilitating higher small mammal diversity in riparian areas. Riparian areas were identifiable from uplands by higher plant cover and supported higher small mammal abundance. Small mammal abundance was related to plant cover and decreased away from riparian habitat. Riparian and upland habitats supported different species, contributing to higher gamma diversity via species turnover between habitats. Differences in plant δ13C between riparian and upland habitats were used to track assimilation of riparian resources by small mammals. Voles and shrews derived significant portions of their carbon from riparian vegetation. Sagebrush vole and woodrat hair was relatively low in δ13C, likely the result of assimilating forbs and annual grasses in upland habitat. Deer and harvest mice were abundant in riparian habitat but assimilated little riparian vegetation indicating that the riparian corridor provided resources other than food. In addition to food resources, plant cover likely provided protection from predators and a moderate microclimate. To our knowledge this is first use of δ13C to trace riparian resources into a vertebrate community and show δ13C as a good proxy for riparian vegetation assimilation.