Concept of Species

Biological Species Concept

The biological species concept defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species.

• Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups.

• A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.

• Species are the members in aggregate of a group of populations that breed or potentially interbreed with each other under natural conditions.

Evolutionary species concept

• A species is a lineage (an ancestral-descendant sequence of populations) evolving separately from others and with its own unitary evolutionary roles and tendencies.
• A species is a single lineage of ancestor-descendant populations which maintain its identity from other such lineages and which has it own evolutionary tendencies and historical fate.
• A species is a population or group of populations that shares a common evolutionary fate through time .

For further study:

http://www.ucl.ac.uk/taxome/jim/Sp/species.pdf