Extinction and the evolutionary process in endangered species: What to conserve?

Abstract

The study of intraspecific variation is important for the management of endangered populations. Current approaches for establishing the value of particular populations for conservation management have been contentious, largely because they draw on different, possibly irreconcilable, scientific concepts. The approach taken here is based on the pattern of variation in molecular or morphological traits. Basic entities for conservation are (groups of) populations whose members exhibit diagnosable characters, consistent with the phylogenetic species concept. Cladistic theory predicts that the extinction of populations can result in formation of allopatric, diagnosable entities from formerly contiguous patterns of variation, a significant event in the evolution of new species. Hence, the effect of extinction on the origination of new diagnosable groups should be taken into account when assessing what to conserve. A procedure for evaluating the potential for cladogenesis within existing species is proposed, as a basis for conservation decisions. The procedure determines if populations represent “linkers” which, because of the alleles present, connect otherwise diagnosable entities; loss of these populations will leave new phylogenetic lineages of high conservation value. The procedure is illustrated using a case study of clinally distributed variation in the endangered tiger beetle, Cicindela dorsalis. Two geographic areas along the Atlantic coast of North America are identified where extinction of linker population could produce new diagnosable entities. In one of these cases this process apparently has already taken place after the extinction of numerous populations, leaving a diagnosable relict population of high conservation priority. The procedure will be useful to anticipate the effects of future population loss on the distribution and magnitude of the remaining variation, and could provide testable hypotheses of biodiversity loss under conditions of regional and global environmental change.