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A major role of modern zoological parks is to maintain for future reintroduction some 2000 species of larger vertebrates that are likely to become extinct in nature as the result of large-scale habitat changes over the next few hundred years (Soule et al., 1986). One assumption necessary to fulfill this goal is that there will be a natural community waiting to receive the species to be reintroduced. This assumption may not be warranted for two reasons. First, factors which caused the extinction of large vertebrate species are also likely to have had a negative impact on the remainder of the ecosystem. For example, deforestation in the tropics, the major agent of extinction in this century (Erwin, 1988), ultimately results in the localized extinction of most resident plants and animals. Second, the removal of larger vertebrates, particularly those at the top of the food web, may cause additional waves of extinction in complex natural systems (Pimm, 1991). For example, the decline of elephants in South Africa has resulted in forestation of large areas of savannah habitat, a process which may lead to the localized extinction of several species of grazing herbivores (Owen-Smith, 1989). The resulting assemblage of plants and animals will hardly resemble the African savannah ecosystem and may be unsuitable for eventual reintroduction of elephants. |
