Edge Effects and the Extinction of Populations Inside Protected Areas

Lande R., Science241, 1455 (1988).

G. Caughley, J. Anim. Ecol. 63, 215 (1994).

W. D. Newmark, Cons. Biol. 9, 512 (1995); but see J. Berger, ibid., 4, 91 (1990).

Several intensive studies of carnivores have shown that deaths caused by people—especially harvesting—increase overall mortality and result in population decline. This impact of harvesting is marked in two species with low fecundity (black and grizzly bears) as well as one with high fecundity (gray wolf). For each species, the proportion of deaths of radio-collared adults caused by people, and sample sizes, are as follows: gray wolf, 79% (97); black bear, 90% (21); grizzly bear, 56% (16). Data sources: gray wolf: W. B. Ballard, J. S. Whitman, C. L. Gardner, Wildl. Monogr. 98, 1 (1987); W. B. Ballard, L. E. Ayres, P. R. Krausman, D. J. Reed, S. G. Fancy, ibid., 135, 1 (1997); black bear: R. A. Powell, J. W. Zimmerman, D. E. Seaman, J. F. Gilliam, Cons. Biol. 10, 224 (1996); grizzly bear: R. B. Wielgus and F. L. Bunnell,Biol. Cons. 67, 161 (1994).

Data from 22 intensive studies of large carnivores in protected areas indicate that 74% of 635 known-cause deaths were directly caused by people. Proportions and sample sizes for each species are as follows: African wild dog, 61% (105); gray wolf, 83% (86); lion, 50% (62); tiger, 67% (3); Iberian lynx, Felis pardina, 75% (24); spotted hyaena, 49% (56); black bear, 85% (41); grizzly bear, 89% (258). More detailed data are available at http://www.sciencemag.org/feature/data/980867.shl . These proportions are comparable with those recorded in populations known to be declining as a result of harvesting (4), indicating that human-caused mortality almost certainly affects the dynamics of populations in protected areas. In 20 of the studies, radiotelemetry was used to locate dead animals, making it unlikely that the data are strongly biased towards deaths caused by people. Most deaths occurred outside reserve borders, caused by legal and illegal hunting as well as road accidents and accidental snaring. Data on grizzly bears also include legal hunting and control of problem animals inside Yellowstone National Park, which together accounted for 130 of 250 deaths recorded there. Quantitative data are not available for jaguars, snow leopards, or dhole, but persecution outside reserves is recorded as a major threat to all three species. Data sources: African wild dog: R. Woodroffe, J. R. Ginsberg, D. W. Macdonald, The African Wild Dog: Status Survey and Conservation Action Plan[International Union for the Conservation of Nature and Natural Resources (IUCN), Gland, 1997]; gray wolf: G. J. Forbes and J. B. Theberge, and also D. K. Boyd et al., inEcology and Conservation of Wolves in a Changing World, L. N. Carbyn, Ed. (Canadian Circumpolar Institute, Edmonton, 1995); dhole: J. R. Ginsberg and D. W. Macdonald,Foxes, Wolves, Jackals and Dogs: An Action Plan for the Conservation of Canids (IUCN, Gland, 1990); lion: J. Rudnai,Afr. J. Ecol. 17, 85 (1979), C. Packer et al., in Reproductive Success, T. H. Clutton-Brock, Ed. (Univ. of Chicago Press, Chicago, 1988); G. B. Schaller, The Serengeti Lion: A Study of Predator–Prey Relations (Univ. of Chicago Press, Chicago, 1972); P. E. Stander, Madoqua 18, 1 (1991); tiger: M. E. Sunquist, Smiths. Contrib. Zool. 336, 1 (1981); snow leopard and jaguar: K. Nowell and P. Jackson, Wild Cats—Status Survey and Conservation Action Plan(IUCN, Gland, 1996); Iberian lynx: P. Ferreras, J. J. Aldama, J. F. Beltrán, M. Delibes, Biol. Cons. 61, 197 (1992); spotted hyena: H. Hofer, M. L. East, K. L. I. Campbell, Symp. Zool. Soc. Lond. 65, 347 (1993), L. G. Frank, Anim. Behav. 34, 1500 (1986); H. Kruuk, The Spotted Hyaena (Univ. of Chicago Press, Chicago, 1972); black bear: E. C. Hellgren and M. R. Vaughan, J. Wildl. Manage. 53, 969 (1989); R. A. Powell, J. W. Zimmerman, D. E. Seaman, J. F. Gilliam, Cons. Biol. 10, 224 (1996); D. L. Garshelis and M. R. Pelton,J. Wildl. Manage. 41, 912 (1981); grizzly bear: J. M. Peek, M. R. Pelton, H. D. Picton, J. W. Schoen, P. Zager, Wildl. Soc. Bull. 15, 160 (1987); S. T. Knick and W. Kasworm, ibid., 17, 11 (1989); R. B. Wielgus, F. L. Bunnell, W. L. Wakkinen, P. E. Zager, J. Wildl. Manage. 58, 266 (1994); Knight R. R., Eberhardt L. L., Ecology 66, 323 (1985).

IUCN, Protected Areas of the World: A Review of National Systems (IUCN, Gland, 1992). We included protected areas in categories I, II, and IV defined by the IUCN. These categories include national parks, reserves, and sanctuaries established with the primary aim of protecting wildlife.

A summary data set and data sources are available at http://www.sciencemag.org/feature/data/980867.shl.

D. R. Cox, The Analysis of Binary Data(Methuen, London, 1970). A model of the form p(reserve occupied) = {exp [A + B(log reserve area) + C(log reserve age)]}/{1 + exp [A + B(log reserve area) + C(log reserve age)]}, where A, B, and C are constants, was fitted to the data by using the Genstat statistical package [Genstat Committee, Genstat 5 Release 3 Reference Manual (Clarendon Press, Oxford, UK, 1993)]. Parameters were estimated by maximum likelihood to determine which significantly improved the fit of the model. The effects of reserve age and size were assessed by dropping each in turn from the model, to estimate the contribution of each to total deviance. The resulting changes in deviance are distributed as χ², in this case with 1 df.

J. W. A. Grant, C. A. Chapman, K. S. Richardson, Behav. Ecol. Sociobiol. 31, 149 (1992).

Felsenstein J., Am. Nat.125, 1 (1985). . Independent contrasts were calculated by using the program CAIC [A. Purvis and A. Rambaut, Comparative Analysis by Independent Contrasts (CAIC), version 2 (Oxford University, Oxford, 1994)], and a composite phylogeny for the Carnivora (O. R. P. Bininda-Emonds, J. L. Gittleman, A. Purvis, unpublished).

Full data on population densities and home range sizes, separated by study, are available at http://www.sciencemag.org/feature/data/980867.shl . Data sources: African wild dog (as in 10); gray wolf: T. K. Fuller,Wildl. Monogr 105, 1 (1989); ___ and L. B. Keith, J. Wildl. Manage. 44, 583 (1980); R. R. Bjorge and J. R. Gunson, Can. Field Nat. 103, 327 (1989); dhole: A. B. Venkataraman, R. Arumugam, R. Sukumar,J. Zool. Lond. 237, 543 (1995); lion: S. Creel and N. M. Creel, Afr. J. Ecol. 35, 83 (1997); K. G. van Ordsol, J. P. Hanby, J. D. Bygott, J. Zool. London 206, 97 (1985); tiger (as in 10); snow leopard: R. Jackson and G. Ahlborn, Nat. Geog. Res. 5, 161 (1989); jaguar: A. R. Rabinowitz and B. G. Nottingham Jr., J. Zool. London 210, 149 (1986); M. E. Tewes and D. J. Schmidly, in Wild Furbearer Management and Conservation in North America, M. Novak, J. A. Baker, M. E. Obbard, B. Malloch, Eds. (Ontario Ministry of Natural Resources, Toronto, 1987); spotted hyena: L. G. Frank, Anim. Behav. 34, 1500 (1986); H. Kruuk, The Spotted Hyaena (Univ. of Chicago Press, Chicago, 1972); C. Sillero-Zubiriand D. Gottelli, Afr. J. Ecol. 30, 292 (1992); S. R. Creel and N. M. Creel, Cons. Biol. 10, 1 (1996); H. Hofer, M. L. East, Anim. Behav. 46, 547 (1993); black bear: H. J. Novick and G. R. Stewart,Calif. Fish Game 68, 21 (1982); E. C. Hellgrenand M. R. Vaughan, J. Wildl. Manage. 53, 969 (1989); D. L. Doancrider and E. C. Hellgren,ibid., 60, 398 (1996); D. L. Garshelis and M. R. Pelton, ibid., 45, 912 (1981); A. J. Brody and M. R. Pelton, Wildl. Soc. Bull. 17, 5 (1989); G. B. Kolenosky and S. M. Strathearn, in Wild Furbearer Management and Conservation in North America, M. Novak, J. A. Baker, M. E. Obbard, B. Malloch, Eds. (Ontario Ministry of Natural Resources, Toronto, 1987); grizzly bear: R. B. Wielgus and F. L. Bunnell, Biol. Cons. 67, 161 (1994); B. M. Blanchard and R. R. Knight, ibid., 58, 41 (1991); R. B. Wielgus, F. L. Bunnell, W. L. Wakkinen, P. E. Zager,J. Wildl. Manage. 58, 266 (1994); McLellan B. N., Can. J. Zool. 67, 1856 (1989); C. Servheen, J. Wildl. Manage. 47, 1026 (1983).

We thank S. Durant, L. Frank, G. Mace, J. Robinson, P. Rohani, and K. Rose for valuable comments and discussions.