<P> Unlike the Biological Species Concept, a cladistic species does not rely on reproductive isolation, so it is independent of processes that are integral in other concepts . It works for asexual lineages, and can detect recent divergences, which the Morphological Species Concept cannot . However, it does not work in every situation, and may require more than one polymorphic locus to give an accurate result . The concept may lead to splitting of existing species, for example of Bovidae, into many new ones . </P> <P> An evolutionary species, suggested by George Gaylord Simpson in 1951, is "an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies". This differs from the biological species concept in embodying persistence over time . Wiley and Mayden state that they see the evolutionary species concept as "identical" to Willi Hennig's species - as - lineages concept, and assert that the biological species concept, "the several versions" of the phylogenetic species concept, and the idea that species are of the same kind as higher taxa are not suitable for biodiversity studies (with the intention of estimating the number of species accurately). They further suggest that the concept works for both asexual and sexually - reproducing species . </P> <P> An ecological species is a set of organisms adapted to a particular set of resources, called a niche, in the environment . According to this concept, populations form the discrete phenetic clusters that we recognise as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters . </P> <P> A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations . This is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation . In the 21st century, a genetic species can be established by comparing DNA sequences, but other methods were available earlier, such as comparing karyotypes (sets of chromosomes) and allozymes (enzyme variants). </P>

Why is species considered the only natural taxon