Elevation gradients of species-density: historical and prospective views

Studies of elevation dines in diversity and composition of ecological commu nities date back to the origins of biogeography. A modern resurgence of int erests in these elevational dines is likely to contribute important insight s for developing a more general theory of species diversity. In order to ga in a more comprehensive understanding of geographical dines in diversity, t he research programme for montane biogeography should include statistically rigorous tests of apparent patterns, comparisons of patterns among regions and taxonomic or ecological groups of species, and analyses of dines in en vironmental variables concurrent with biogeographical surveys. The conceptu al framework for this research programme should be based on the assumption that elevational gradients in species diversity result from a combination o f ecological and evolutionary processes, rather than the presumed independe nt effects of one overriding force. Given that montane ecosystems are hot s pots of biological diversity, an expanded and integrated programme for biog eographic surveys in montane regions should provide valuable insights for c onservation biologists.