Human influence on mammalian biodiversity of public lands in the United States.

Abstract

Many factors affect biodiversity and species richness such as size of reserve, habitat diversity, land use outside the reserve, latitude, precipitation, degree of isolation, distance to species "source", and rate of disturbance. I determined the effects of reserve size, habitat diversity, and land use outside the reserve on mammalian species richness and assemblage, number of disturbed site species and undisturbed site species on reserves in the conterminous United States. In January of 1995, 429 letters were sent to the offices of national parks, national wildlife refuges, and national forests requesting information on mammals found within the reserves. Managers from 308 reserves replied. Questionnaires requesting additional information on acreage of the reserve, habitat types, surrounding land use, and confidence that the mammal list accurately represented the mammalian assemblage found on the reserve were sent back to the 308 reserve managers. After receiving the confidence rating for each reserve, 175 were found to be insufficient to use in my study. The remaining 133 produced useable data. To investigate the relationship between the size of an area and species richness, curvilinear regression and species-area curve equations were used. These data fit the species-area curve (R2=0.45, z = 0.12), therefore, the rest of the analyses was conducted with confidence these data accurately represented a true relationship between size of reserve and species richness. Size of the reserve had more of an influence on undisturbed species richness (R2=0.63) than on disturbed species richness (R2=0.20). When using simple linear regression to determine the relationship between habitat diversity and species richness, only a slight trend was noted (P = 0.02; r = 0.04). Since the number of habitats are discrete groups, an analysis of covariance was used to determine the differences in species richness among number of habitats. In reserves with 7 to 9 habitat types, the overall species richness and undisturbed species richness was significantly higher. The number of habitat types within a reserve did not have a significant effect on disturbed species richness due to the habitat requirements of disturbed species. Within each habitat type group, undisturbed species richness was significantly less than disturbed species richness. Land use outside the reserve did not have a significant effect on overall, disturbed, and undisturbed species richness. Within each land use group, undisturbed species richness was significantly less than disturbed species richness. Species area curve equations can explain conditions of the habitat for particular species being tested. The z value for undisturbed species richness was 0.26, which is consistent with true, oceanic islands showing the strong isolating effect of disturbance outside the reserve on the species inside the reserve. The c value for undisturbed species was very low, which means the environmental conditions for these types of species is poor.