Species

Preserving species, the major focus of conservation efforts, requires a clear definition of species. Three definitions are widely employed. One (“morphological species concept”) is based on clustering individuals based on appearance. A second (“phylogenetic species concept”) uses relationships based on DNA sequences. A third (“biological species concept”) is based on the failure of individuals of one species to successfully breed with individuals from another and is used mainly to study the process whereby new species form. Over 2 million morphological species have been described. More than 6 million may remain to be discovered. The number may be even larger because cryptic species, which are outwardly similar but genetically different, may be common, and because parasites may be more diverse than currently appreciated. These undescribed species fall under the radar of conservation initiatives. While species continue to be the main unit of conservation, distinct populations also contribute to overall biodiversity. The Endangered Species Act in the United States allows the listing of population segments, even when the species as a whole is not threatened.