SPECIES CONCEPTS (DIFFERENT SPECIES CONCEPTS)
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.
- 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
- BEHAVIORAL (barriers to isolation)
2. POST-ZYGOTIC :-
- HYBRID INVIABILITY
- REDUCED FITNESS OF HYBRID OFFSPRING
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
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.
- 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.