Species concepts and species reality: salvaging a Linnaean rank

Abstract

The validity of the species category (rank) as a distinct level of biological organization has been questioned. Phenetic, cohesion and monophyletic species concepts do not delimit species-level taxa that are qualitatively distinct from lower or higher taxa: all organisms throughout the tree of life exhibit varying degrees of similarity, cohesion, and monophyly. In contrast, interbreeding concepts delimit species-level taxa characterized by a phenomenon (regular gene flow) not found in higher taxa, making the species category a distinct level of biological organization. Only interbreeding concepts delimit species-level taxa that are all comparable according to a biologically meaningful criterion and qualitatively distinct from entities assigned to other taxonomic categories. Consistent application of interbreeding concepts can result in counterintuitive taxonomies -e.g. many wide polytypic species in plants and narrow cryptic species in animals. However, far from being problematic, such differences are biologically illuminating -reflecting differing barriers to gene flow in different clades. Empirical problems with interbreeding concepts exist, but many of these also apply to other species concepts, whereas others are not as severe as some have argued. A monistic view of species using interbreeding concepts will encounter strong historical inertia, but can save the species category from redundancy with other categories, and thus justify continued recognition of the species category.

Genetic differentiation and history of populations of the Italian treefrog Hyla intermedia: lack of concordance between mitochondrial and nuclear markers

“…Only the joint study of both nuclear and mitochondrial markers, has made it possible to put in evidence the existence of a more complex evolutionary history. In the face of the extensive use of a single kind of marker in studies of molecular taxonomy and systematics, the case study we have presented here constitutes a serious cautionary note, and a strong argument against the use of single markers and/or genetic distances for identifying species or investigating evolutionary processes at levels other than the single marker studied (see also Ferguson 2002; Hudson and Coyne 2002;Lee 2003). This latter point appears of particular relevance for taxa such as amphibians, whose taxonomy and systematics have been so deeply revised in the light of genetic studies (Veith 1996;Borkin 1999).…”

Molecular evidence of conspecificity of South African hares conventionally considered Lepus capensis L., 1758

“…Any of the ''Interbreeding Species Concepts'' (biological-, genetic-, recognition-, reproductive competition-, generic-, cladistic-or ''Hennigian'' species concepts; see e.g., Lee 2003;Coyne andOrr 2004, Baker andBradley 2006) delimits the presently studied hares to a single species (i.e., L. capensis L., 1758), contrary to a ''Similarity Species Concept'', such as a ''Phenetic Species Concept''. Supposedly, Palacios et al (2008) have used their morphological distinction together with their chorological data not only in the context of a ''Phenetic Species Concept''; they rather may have used it as a proxy of reproductive isolation between ''L.…”

Evolution isolierter Teilpopulationen der Laubholz-Säbelschrecke Barbitistes serricauda (FABRICIUS 1798)

“…bspw. Bock 2003, Lee 2003 von den dargelegten Überlegungen nicht betroffen, da sie eine andere Fragestellung verfolgt. …”