MOLECULAR SYSTEMATICS AND THE MULTIDIMENSIONAL CONCEPT OF SPECIES

Following a critical review of the species concepts and stressing the need for a single, general classification system to serve both systematists and evolutionary biologists, the author seeks to identify a conceptual framework where matching of taxonomic characters to the biological properties of species is maximized. Sympatric and synchronic populations of amphigonic organisms can almost unequivocally be identified as species when reproductive gaps occur between them. In such situations species are recognized by appropriate descriptors (characters) as genetic units and ecological units. Multivariate statistical methods provide a powerful tool to analyse more complex situations where non-amphigonic organisms and/or allopatric populations are investigated, on condition that appropriate character sets are considered. The increasing availability of molecular data for analysis certainly enhances the recognition of species as genetic unities, whilst much of the ecological role of an organism may be read from a careful choice of morphometric and ethological descriptors. On these premises it is suggested that species can be defined as groups of individuals (populations) which are discretely separated from other such groups in the character space. This definition is phenetical in its form but biological in its meaning since character sifting and weighting are considered essential features at the operational level.