The biodiversity bandwagon: the splitters have it

The accurate estimation of biodiversity has become one of the most important biological and conservation concerns of the 21st century. An unbiased estimate of biodiversity requires an unambiguous measurement unit. The most commonly used unit is the ‘species’, and though it is implicitly accepted as valid, consistent and appropriate, there has been little consensus over the many different species concepts proposed over the years1 . Among these, the Biological Species Concept2 has been widely used, but it has come under fire due to the arbitrariness of the genetic distance or morphological divergence that is generally used to assign species status3,4. Recently, the phylogenetic species concept5 , which recognizes diagnosably distinct taxa, has been used extensively for some groups. In the context of conservation, ‘management units’and ‘evolutionary significant units’ have been proposed6,7, but most studies still use species as the basic unit without examining or explaining which definition of ‘species’ they are using.