NATURE RESERVES: DO THEY CAPTURE THE FULL RANGE OF AMERICA'S BIOLOGICAL DIVERSITY?

The intention and practice of conservation reserve selection are different. A major reason for systems of reserves is to sustain biological diversity. This involves protecting examples of as many natural features, e.g. species, communities or environments, as possible. In reality, however, new reserves have rarely been dedicated for their representation of features. Furthermore, the opportunism that has characterized the development of reserve systems can actually jeopardize the representation of all features in reserves through the inefficient allocation of limited resources. More systematic approaches are essential if reserves are to play their role in protecting biodiversity. Some basic principles for conservation planning are emerging from recent systematic procedures for reserve selection. These principles will help to link intention and practice. Copyright © 1993. Published by Elsevier Ltd.

For trees, mammals, birds, reptiles, insects, and amphibians, the species richness on mountaintops is generally less than that of lowland areas. Coincident with this decline in species richness with increasing elevation is an increase in the altitudinal range of species. This pattern is analogous to the relationship between the latitudinal range of species and latitude (Rapoport's latitudinal rule). Both of these Rapoport phenomena, the latitudinal and the new elevational rule discussed here, can be explained as being results of differences in the breadth of climatic conditions organisms experience along the geographical gradients. The influence of latitudinal or altitudinal range size on local species richness is poorly understood, but the tendency for range margins to fall in species-rich, rather than species-poor, areas may mean that species-rich communities contain many species that are maintained only through immigration. The presence of these persistent but locally non-self-maintaining populations may explain the increased number of species found in rich communities as compared to species-poor communities without the need to invoke other differences in local species interactions.