Biodiversity hotspots and beyond: the need for preserving environmental transitions

A great deal of effort and many resources are directed at identifying and conserving regions of high species diversity 1xBiodiversity hotspots for conservation priorities. Myers, N. et al. Nature. 2000; 403: 853–858Crossref | PubMed | Scopus (9363)See all References, 2xBiodiversity, hotspots and defiance. Kitching, R. Trends Ecol. Evol. 2000; 15: 484–485Abstract | Full Text | Full Text PDF | Scopus (8)See all References. Although defining ‘biodiversity hotspots’ helps prioritize areas for conservation, overemphasis on such sites ignores the need for preserving adaptive variation across environments. A more comprehensive approach would be to include regions important to the generation and maintenance of biodiversity, regardless of whether they are ‘species rich’. With climate change threatening large-scale shifts in species distributions and the habitats on which they depend, the hotspots of today are unlikely to be the hotspots of tomorrow. Only by maximizing adaptive variation can one hope to preserve the evolutionary response to changing climate and environmental conditions.The ‘hotspot’ approach to species preservation is risky, particularly when applied at a local scale. Preserving populations in only one pure habitat type, such as central tropical rainforests, is analogous to building an investment portfolio made up of a single stock. Diversifying risk by conserving populations from across diverse habitats will ensure that adaptive variation is maximized. Species are assemblages of populations that are often distributed across a landscape of habitat types and those populations have specific adaptations to regional environmental conditions. Populations are being lost at a much higher rate than are species 3xPopulation diversity: its extent and extinction. Hughes, J.B. et al. Science. 1997; 278: 689–692Crossref | PubMed | Scopus (290)See all References3 and, consequently, the loss of populations in unique habitats could result in the loss of novel adaptations that are necessary to meet future environmental challenges 4xConsidering evolutionary processes in conservation biology. Crandall, K.A. et al. Trends Ecol. Evol. 2000; 15: 290–295Abstract | Full Text | Full Text PDF | PubMed | Scopus (990)See all References4. A strategy is urgently needed that preserves the adaptive diversity represented by the range of populations within a species, thus assuring the maximum potential of that species to respond to future environmental conditions.We believe that one strategy for conserving the maximum amount of adaptive variation is to preserve populations that occur along environmental gradients, thus preserving the full range of populations across habitats, as well as the unique traits of those populations. Adaptive diversity within species is often well represented along environmental gradients or ecotones that represent the transition from one habitat type (e.g. tropical rainforest) to another (e.g. grassland or savanna) 5xEndler, J.A. See all References5. Recent research on a wide range of taxa suggests that environmental gradients are important in diversification and speciation 6xSchluter, D. See all References, 7xEcotone: speciation-prone. Schilthuizen, M. Trends Ecol. Evol. 2000; 15: 130–131Abstract | Full Text | Full Text PDF | PubMed | Scopus (44)See all References, 8xNonrandom mating in Drosophila melanogaster laboratory populations derived from closely adjacent ecologically contrasting slopes at ‘Evolution Canyon’. Korol, A. et al. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 12637–12642Crossref | PubMed | Scopus (79)See all References, 9xRapid evolution of reproductive isolation in the wild: evidence from introduced salmon. Hendry, A.P. et al. Science. 2000; 290: 516–518Crossref | PubMed | Scopus (333)See all References.There is little current emphasis on the conservation of ecological gradients. Recent attempts to prioritize conservation areas ignore these regions entirely 1xBiodiversity hotspots for conservation priorities. Myers, N. et al. Nature. 2000; 403: 853–858Crossref | PubMed | Scopus (9363)See all References, 10xThe Global 200: A representation approach to conserving the Earth's most biologically valuable ecoregions. Olson, D.M. and Dinerstein, E. Conserv. Biol. 1998; 12: 502–515CrossrefSee all References. We maintain that a more sound conservation strategy would focus on both hotspots of biodiversity and on associated transitional zones. Given future uncertainty, preserving such areas will maximize the probability of a viable response at the species level to changing climatic conditions. In the absence of extensive data on population variation, we suggest that this diversity is likely to be summarized along environmental gradients. Saving the biota of the Earth will require greater efforts to preserve not only the pattern of biodiversity but also the processes that generate and maintain it. Integrating information on both pattern and process will ensure that the capacity for populations to change with changing environments is preserved.