SPECIES CONCEPTS (DIFFERENT SPECIES CONCEPTS)

SPECIES CONCEPTS (DIFFERENT SPECIES CONCEPTS)

Introduction

What is a species?

According to the most widely used species definition, the biological species concept, a specie is a group of organisms that can potentially interbreed, or mate, with each other to produce viable, fertile offspring.

A group or class of animals or plants (usually constituting a subdivision of a genus) having a certain common and permanent characterstics which clearly distinguish it from other groups.

CONCEPT OF SPECIES

Species Concepts

  • An idea of what kind of entity is represented by the word SPECIES.
  • There are several concepts recognizing the special reality of species
  • SPECIES CRITERIA= standards used for species recognition=operationalism

Biological Species Concept

  • Given by Mayr in 1942.
  • Species are groups of interbreeding natural population that are reproductively isolated from other such groups.
  • Species are designated on absence of gene flow.
  • Emphasis on REPRODUCTIVE ISOLATION.

Reproductive Isolating Mechanism

PRE-ZYGOTIC :- 

  • ECOLOGICAL
  • TEMPORAL
  • BEHAVIORAL (barriers to isolation)

2. POST-ZYGOTIC :-

  • HYBRID INVIABILITY
  • STERLITY
  • REDUCED FITNESS OF HYBRID OFFSPRING
CONCEPT OF SPECIES

Phylogenetic Species Concept

“Species is a group of organism whose members are descended from common ancestor and have unique evolutionary history.” Subspecies not recognized
STRENGTH : considers ancestry, genetic similarity, evolutionary process
WEAKNESS : does not consider reproductive habitats

CONCEPT OF SPECIES

Evolutionary Species Concept

  • Given by Simpson in 1951.
  • An Evolutionary species is a single lineage of ancestor-descendant populations that maintains its identify from other such lineages and that has its own evolutionary tendencies and historical fate.
  • This definition accomodates both sexual and asexual forms as well as fossils. 

Nominalistic Species Concept

  • Given by Occan and his followers
  • Nature produces individuals only and nothing more, species have no actual existence in nature

DRAWBACKS -: Nominalist misinterpreted the relation between similarity and relationship

It is a established fact that species are products of evolution.

Recognition Species Concept

  • A Species is a set of organism that recognize one another as potential mates, they have a shared recognition system.”
  • Emphasis on reproductive isolationing mechanism to keep species apart
  • Sometimes referred to as REPRODUCTIVE SPECIES CONCEPT
  • EXAMPLE: AMERICAN CRICKET

Morphological Species Concept

  • Given by Cronquist in 1978.
  • “A species is a community, or a number of related communities, whose distinctive morphological characters are, in the opinion of a competent systematist, sufficiently definite to entitle it, or them to a specific name.”
  • May be applied to both sexual and asexual organisms.

Ecological Species Concept

  • Focus of species characterization is on similarity of niche and ecological role.

-> Strength : considers species role in an ecosystem.

 -> Weakness : geographically widespread populations that don’t actually interbreed may be considered the species.                              

Conclusion

  • The categorization and maintenance of species records is important for science and conservation.
  • For identifying an individual species, typically scientists will first consider Biological Species Concept, then descent from common ancestry and genotypic and phenotypic cohesion.
  • Species concepts are still subject to debate.

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