The equilibrium theory of island biogeography proposes that on an island of a given area, there exists an equilibrium number of species when the rates of immigration and local extinction of species are equal (MacArthur and Wilson 1967). This theory has been applied to park systems because parks may act as functional islands when surrounding unprotected land is cleared of natural vegetation. Alteration of these surrounding habitats isolates these parks and reduces the effective area, causing a decrease in the equilibrium number of species. In animal communities, this process is called faunal collapse (Soule et al. 1979).The effects of park isolation and faunal collapse have been studied for mammals in Rocky Mountain parks (Picton 1979, Newmark 1986, Glenn and Nudds 1989). In western U.S. parks, extinctions were more numerous in smaller or older parks (Newmark 1987). Area, topographic diversity, and habitat diversity have been correlated with mammal species richness in western North American parks (Picton 1979, Newmark 1986). Initial population size was also related to the extinction probability of a species (Newmark 1986). It has been proposed that all parks in a region are subject to similar factors influencing local extinctions, and therefore a similar suite of species should become locally extinct in all parks (Patterson and Atmar 1986, Patterson 1987). This means that a nested subset pattern is produced, where parks with low species richness contain mainly species already present in parks with high species richness. This pattern was not found for Canadian parks, where even small parks contained different species assemblages (Glenn 1990). The objectives of this three-year study are to: (i) identify mammal species that have become locally extinct in each of the Rocky Mountain National Parks; (ii) distinguish between hypotheses regarding the causes of these local extinctions in National Parks; (iii) determine if the same species become locally extinct in all parks; and (iv) identify potential sites for future protection of species prone to extinction.
Glenn, Susan M.; Chapman, Brian; Rudman, Rebecca; and Butler, Ian
"Biogeography of Mammals in Rocky Mountain National Parks,"
University of Wyoming National Park Service Research Center Annual Report: Vol. 15
, Article 4.
Available at: http://repository.uwyo.edu/uwnpsrc_reports/vol15/iss1/4