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whose populations and species have had a shared, unique evolutionary history, thus allowing for the conservation of communities of organisms that have high levels of genetic endemism or uniqueness.

Intraspecific Phylogeography

The term intraspecific phylogeography denotes the connection between biological systematics, population genetics, and biogeography, the study of the distribution of organisms in geographic space and the factors that led to that distribution (Avise and others 1987). In principle, any biological characteristic can be used for this purpose, but intraspecific phylogeography now mostly is associated with the study of molecular markers, especially mitochondrial DNA (in animals) or chloroplast DNA (in plants). By determining the detailed genetic and evolutionary relationships of populations within a species (or CU), and superimposing that intraspecific molecular phylogeny on a geographic map, one can infer the processes that historically determined the current distribution of organisms. One also can use this approach to identify the geographic location of genetically distinct populations (that is, populations that substantially differ from one another by the frequency of genetic traits rather than by the presence or absence of those traits) or MUs, which might deserve special attention if specific conservation measures become necessary to preserve a given species. The identification of specific MUs and their geographic location currently has one of the highest priorities in most efforts that use molecular markers for conservation purposes, and intraspecific phylogeography provides a theoretical framework to accomplish this.

Case Study. Among the animal species currently listed by the International Union for the Conservation of Nature (IUCN), the Convention on International Trade in Endangered Species (CITES), and the US Department of the Interior as endangered, the Sumatran rhinoceros (Dicerorhinus sumatrensis) is one in greatest need of special attention and immediate wild-population (or in situ) management. Historically, this species inhabited most of the Indochinese peninsula, from Burma (Myanmar) to Vietnam, and south to Malaysia and the islands of Sumatra and Borneo. Destruction of habitat and hunting have led to a rapid decline of this species over the last 2 decades. Only a few confirmed populations remain on peninsular Malaysia, Borneo, and Sumatra. Because of the dire situation of this species, translocation programs have been proposed that would move individuals that are scattered among fragments of unsustainable forest and concentrate them in protected zones of natural habitat (Foose and van Strien 1995). However, it is important to remember that the objectives of any conservation effort should be not only to maintain a collection of organisms, but also to preserve the maximal amount of existing genetic variability within a species and to maintain the evolutionary historical integrity of its wild populations.

Geographic mapping of the distribution of mitochondrial-DNA (mtDNA) variants among Sumatran rhinoceros populations (Morales and others 1997), using both molecular-systematic and population-genetic methods, reveals two phylo-geographic features that are important to the conservation of the Sumatran rhinoceros. First, a phylogenetic tree of mtDNA haplotypes, overlaid on the distri-