Diagnosing Units of Conservation Management

Species-oriented conservation programs attempt to analyze and maintain intra-specific variation in order to maximally preserve biological diversity. The "evolutionarily significant unit" has become an operational term for a group of organisms that should be the minimial unit for conservation management. No generally accepted definition for this term exists that would be the basis for the evaluation of these units in practical conservation situations. Currently, taxonomic decisions in species conservation are mostly based on the biological species concept. But the universal application of criteria of reproductive isolation or phenetic similarity to delimit conservation units is problematical. We favor a definition for evolutionarily significant units based on patterns of variation. In the theoretical framework of the phylogenetic species concept, conservation units are delimited by characters that diagnose clusters of individuals or populations to the exclusion of other such clusters. Characters are used for cladistic analysis to infer hypotheses of the phylogenetic relationships of individuals, and differentiated populations are diagnosed using population aggregation analysis. Characters can be based on genetic, morphological, ecological, or behavioral information, provided they are inferred to be heritable. The use of cladistics and population aggregation analysis has the potential to make the evaluation of evoluntionarily significant units objective and testable, an important consideration in politically controversial cases. Our cladistic approach is demonstrated by the evaluation of potential conservation units in the endangered tiger beetles Cicindela dorsalis and C. puritana .