• biodiversity;
  • exurban development;
  • land use;
  • ranching

ABSTRACT. Rural private lands in the Mountain West of the United States are undergoing a profound land-use conversion, from agriculture to low-density residential or exurban development, though little scientific study documents the ecological consequences of this change. Nongovernmental conservation organizations are working with ranchers to keep rangeland out of development and in ranching, ostensibly because these organizations believe that biodiversity is better protected on ranches than on exurban developments. We compared plant and wildlife communities across the principal rural land uses in the Mountain West: protection, livestock ranching, and exurban development. Native plant and faunal biodiversity was better maintained on ranches and protected areas than on exurban developments. Exurban developments favored species that were nonnative or adapted to human-altered environments. The continued conversion of ranches to exurban development suggests a long-term alteration of the region's natural heritage.