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Population Processes and Biological Diversity Michael S. Gaines, Johanna Foster, James E. Diffendorfer, Wendy E. Sera, Robert D. Holt, and George R. Robinson Department of Systematics and Ecology University of Kansas Lawrence Introduction A major goal of conservation biologists is to preserve biological diversity. The accelerating destruction of habitats by human beings has resulted in fragmented landscapes, which has led to a reduction in biological diversity (Wilson 1988). As fragmentation increases, it leads to a decrease in average habitat patch size and an increase in average distance between patches (Wilcox 1980). Both habitat loss and insularity may reduce population sizes to such low levels that species may go extinct. The formidable task facing conservation biologists is to develop land management programs to protect species. Successful programs must be based on a thorough understanding of ecological and evolutionary processes of the populations under consideration. The need for information about population processes for the protection of threatened and endangered species is underscored by the continuing debate whether a single large reserve or several small reserves will protect more species (Wilcox and Murphy 1985, Wiens 1989). Reserve design is still a contentious issue after 15 years because not all species respond in the same way to habitat fragmentation (Wilcove et al. 1986). An interesting question related to the preservation of biological diversity is: What fundamental unit should be preserved? Should the focus be on a local population, a set of interacting local populations (metapopulations), community or ecosystem. As the level of biological complexity increases from populations to ecosystems, the number of interactions increases, making higher levels of biological organization more difficult to study. These higher levels of biological organization have emergent properties resulting from interspecific interactions, thus communities and ecosystems are not simply the sum of their parts. Ideally, we would like to preserve ecosystems but they are not amenable to experimentation. The advantage of a population approach allows for experimental manipulation. Management decisions about the conservation of biological diversity need to be made quickly because there is neither enough time nor funds to study the population dynamics of all species in a community. Under these difficult circumstances the manager is required to decide which population should be studied. The choice is often based on political forces, rather than on sound biological reasons. An under- standing of the population biology of certain keystone species (Paine 1966) might be particularly useful in the development of management programs to conserve a large fraction of the entire community (Gilbert 1980, Terborgh 1986, Simberloff 1988). Population changes in keystone species that provide habitat structure for other species may have profound effects on biological diversity. For example, lichens in some Austrian alpine grasslands required spaces created by the sedge Carex curvula 252 ? Trans. 57" N. A. Wildl. & Nat. Res. Conf. (1992)