Evaluating the contribution of small National Park areas to regional biodiversity

Conservationists have questioned whether setting aside small national parks and reserves for conservation is an effective approach to maintaining regional diversity. We summarized the available information on the species richness of vascular plants, mammals, and birds for 44 U.S. National Park System units in the Rocky Mountain Region. Species richness increased as park area increased (Species number = 246 + (102*log Area); r(2) = 0.48; P < 0.005). However, species density (species km(-2)) showed a negative relationship with area (log Species number/km(2) = 5.5 -(0.8*log Area); r(2) = 0.94; P < 0.001). Due to species composition differences among park units, small units add a considerable number of species to regional species lists. Differences in species composition (measured as percent overlap) had a negative relationship with increasing distance from the target park-Yellowstone National Park-ranging from 7% to 54%. The number of species reported as unique to a unit varied considerably by unit and by taxon; this is because several units cover a wider range of habitats than occur in a single large reserve of comparable size. We used species-area curves to estimate that the establishment of a new 100 km(2) reserve would include 718 species of plants, birds, and mammals and would add approximately 84 unique species to the reserve system. Adding the same size area to an existing small, medium, and large reserve would only add 35, 7, and 1 species, respectively. Most small parks in the region were initially established as cultural/historical sites, yet our results illustrate the role of the smaller National Park System units as biological refugia, migration/dispersal rest stops and corridors, and living outreach programs. Small units have a disproportionate share of regional biodiversity and an understated role in the conservation of biodiversity in the region.