Fish species - how and why

摘要

It is argued, with selected examples from freshwater fish systematics,that species should be viewed as an expression of self-perpetuatedclustered variation in nature, conforming to the phylogenetic speciesconcept. The importance of species lies in the functional and structuralsignificance of their diagnostic characters. Species can be nested bytheir characters into a tree diagram (phylogeny) or hierarchical alignmentstructure (classification) of character distribution, which may be takento reflect evolution, the unifying theory of organismal diversification.The phylogenetic species concept, which emphasizes recognition of apattern of variation, describes better than any other proposed concept theunits called species by systematists. Other concepts are based onprocesses and normally do not permit recognition of particular taxa.Species have unique histories, and speciation may proceed by differentmechanisms. Whereas it may be postulated that speciation entails anirreversible change in the genetic structure of taxa, recognized byphenotypic expression and apparently also maintained to a large extent byselection for a particular phenotype, species recognition must remainindependent of assumptions about species history and spatial distribution.Species are monophyletic taxa and the species category does not differsignificantly in phylogenetic regard from other systematic categories.Species as such are not necessarily evolutionary units. It is recommendedto apply species names with reference to the diagnostic characters of thespecies and to abandon the type specimen described by the InternationalCode of Zoological Nomenclature as a nomenclatural reference unit.[References: 69]