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RESERVE SIZE, LOCAL HUMAN DENSITY, AND MAMMALIAN EXTINCTIONS IN U.S. PROTECTED AREAS

Parks, S.A. & Harcourt, A.H.

In Conservation Biology

ABSTRACT
We examine quantitatively the interaction of reserve size and surrounding local human density in the U.S.A., and their relative impact on extinction of large mammals in western U.S. national parks. Data on reserve size and human density were obtained from publicly available sources. Local human density was calculated as the mean density in the 50 or 100 km zone surrounding the reserves' borders. Reliable extinction data are extraordinarily hard to find. Using a variety of definitions of extinct, we collated information on extinctions of large mammals (> 5 kg) within 13 western national parks that span the size of US national parks as a whole. Human density surrounding reserves varies considerably. Overall, small reserves are in areas of higher human density than are large reserves (p < 0.0001, r2 = -0.24, n = 864 (excluding Hawaii)), many of them at higher local density than the mean for the contiguous U.S.. Extinction rates of large mammals correlate significantly with local human density, but not with park area. These findings together emphasize that 1) processes occurring outside of a reserve's boundary may unexpectedly strongly affect species within the reserve; 2) small reserves might suffer the double jeopardy of not only their size, but also their situation in especially adverse surrounds; and thus 3) small reserves might suffer more intense edge effects than large reserves. If so, conservationists might usefully incorporate the relationship into models, as well as into management decisions.