Abstract

In both folk taxonomy and science, the idea of species is based on the observation that phenotypic variation is discrete and not continuous. The definition of the species category, the "what," must therefore be restricted to these empirically demonstrable facts. To avoid circularity, concepts about the biological nature of species, the "whys," must be kept separate from the criteria by which individual species are circumscribed. Such ideas are models and can only be judged in terms of their capacity to bring observations into a meaningful context. The Biological Species Concept (BSC), the Evolutionary Species Concept (EvSC) and the Ecological Species Concept (EcSC) are models, not definitions. The BSC has its principal flaw in its inability to deal with uniparentally reproducing organisms. It fails to identify the driving force of speciation. It therefore fails to predict diversity and to explain why different species have different reproductive strategies. The EvSC fails to explain why different lineages are phenetically different. It fails, therefore, to explain why species arise, and why there are differences in diversity and reproductive strategies. The EcSCh as the potential to make a direct connection between environment and phenetic variation patterns. It provides a useful conceptual framework for experimentation and observation at the interface between taxonomy and ecology and has the potential to explain on a universal basis variation in diversity and reproductive patterns. In some taxonomically difficult cases it also sheds light on the nature of variation patterns and might therefore help in taxonomic judgment where the BSC is conceptually inapplicable and the EvSC fails to provide useful concepts.