CHOOSING AMONG ALTERNATIVE PHYLOGENETIC SPECIES CONCEPTS

Several different ''phylogenetic'' species concepts have been proposed, and we consider how to choose among them. There appear to be two main approaches. ''Character-based'' concepts define species on the possession of characters, whereas ''history-based'' concepts are based on historical. relatedness. Under the latter view, characters may be used to discover species in practice but they are not viewed as defining attributes of species. To illustrate the distinction we discuss a character-based approach utilizing ''diagnostic'' characters and a history-based approach using genetic coalescence. We argue that the choice between character- and history-based concepts is primarily determined by one's understanding of systematics. If the goal of systematics is simply to describe the hierarchical distribution of characters (''pattern cladistics''), a character-based definition of species is required. In contrast, if systematics is concerned with inferring the evolutionary relationships of organisms (''evolutionary phylogenetics''), a history-based definition of species is needed. We hold the view that phylogenetic systematics is concerned with evolutionary history and therefore we maintain that a phylogenetic species concept should be history-based.