Concept of species-Morphological, Biological and Phylogenetic

Concept of species-Morphological, Biological and Phylogenetic

Species is the fundamental unit of taxonomic classification. Greek philosopher Plato proposed concept of “eidos” or species and believed that all objects are shadows of the “eidos”. According to Stebbins (1977) species is the basic unit of evolutionary process. Species is a group of individual organisms which have the following characters.

1.        A population of organisms which closely resemble each other more than the other population.

2.        They descend from a common ancestor.

3.        In sexually reproducing organisms, they interbreed freely in nature, producing fertile offspring.

4.        In asexually reproducing organisms, they are identified by their morphological resemblance.

5.        In case of fossil organisms, they are identified by the morphological and anatomical resemblance.

Species concepts can be classified into two general groups. Concept emphasizing process of evolution that maintains the species as a unit and that can result in evolutionary divergence and speciation.

Another concept emphasises the product of evolution in defining a species.

Types of Species

There are different types of species and they are as follows:

1. Process of evolution - Biological Species

2.   Product of evolution - Morphological Species and Phylogenetic Species

Morphological Species (Taxonomic species)

When the individuals are similar to one another in one or more features and different from other such groups, they are called morphological species. These species are defined and categorized with no knowledge of phylogenetic history, gene flow or detailed reproductive mechanisms.

Biological Species (Isolation Species)

According to Ernest Mayr 1963,“ these are groups of populations that interbreed and are reproductively isolated from other such groups in nature”.

Phylogenetic Species

This concept was developed by Meglitsch (1954), Simpson (1961) and Wiley (1978). Wiley defined phylogenetic species as “an evolutionary species is a single lineage of ancestor descendent populations which maintains its identity from other such lineages which has its own evolutionary tendencies and historical fate”.