What is a species?

– groups of actually or potentially interbreeding individuals within an area, which are reproductively isolated from other such groups (Mayr 1942).  

Biological Species Concept

Phylogenetic Species Concept

(Cladistic Species Concept) – the smallest diagnosable cluster of individual Organisms within which there is a parental pattern of ancestry and descent (Cracraft 1983).Genetically distinct population with a monophyletic lineage.

Evolutionary Species Concept

- a lineage which occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from all other lineages outside of its range (Van Valen 1976).

Recognition Species Concept

– defines species from the basis of gene recombination (Paterson 1985).

Cohesion Species

– emphasizes the mechanisms (gene flow, natural selection) that results in species cohesion (Tempelton 1989).

Evolutionary Significant Unit (ESU)

• a population of organisms that is considered distinct for purposes of conservation.

- Definitions of an ESU generally include at least one of the following criteria:

1. Current geographic separation 2. Genetic differentiation at neutral markers among

ESUs caused by past restriction of gene flow 3. Locally adapted phenotypic traits caused by

differences in selection.

The definition of a species is a static concept while the process that generate species is dynamic – here lies the major problem with the concept of the species!