Species is the fundamental biological unit of classification. John Ray, an English naturalist coined the term species.

(i) Morphological Species Concept:

Taxonomist defined species as a group of individuals that resemble each other in most of their visible characters or morphological characters. This concept is not applicable to some animals. E.g. Males of some birds are colourful with beautiful plumage than the females.

(ii) Biological Species Concept:

The most influential species concept has been the biological species concept has been the biological species concept advanced by Dobzhansky (1937) and propagated Mayr. Mayr (1942) states that species is group of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. The above concept can be summarized below.

A species is a biological unit. They possess distinct morphological characters. They interbreed among themselves. They are reproductively isolated from other species. They have a common gene pool. There is free flow of genes among themselves and each species has the capacity to give rise to new species.

(iii) Ecological Species Concept:

The species can share same ecological niche which is not utilized by another species.

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Genetic Species Concept:

Species is group of organisms, which has a close genetic similarity.

Phylogenetic Species Concept:

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Cracraft (1983) defined the phylogenetic species concept as a monophyletic group composed of a smallest group of individual organism within which there is a parental pattern of ancestry and descent.