SPECIES CONCEPT-Definitions of Species given by different Taxonomist

(A) John Ray Definition of Species :

"On the basis of reproduction".

" Alt the animals that originated by same parents belongs to the same species"

 Note - Above definition of species can't define species exactly and accurately because in nature there is continuous evolutionary process so that one species may changed to other species.

(B) Linnaeus Definition of Species : On the basis of morphology (Traditional species concept or morphological species concept or static specie: concept)

" All the animals that are same in shape, size, colour belongs to Same species"

Linnaeus believed that the species are fixed and unchangeable means consistency of species.

Note -Above definition of species is not fit because in a species population they can vary in shape, size and colour so that asexual organism may be assigned to species only on grouping of clones that have tht same morphology and biochemistry.

Objection of Static species concepts: by Lamark

Book - Philosophic zoologique

He was the first to discard the idea of "fixity of species" and " static species concept" as proposed earlier by Aristotle and Linnaeus

(C) Mayr Definition of Species :

 "On the basis of interbreeding" (Biological species concept) 1940.

" population of interbreeding individuals with common gene pool" and are reproductively isolated.

Support of biological species concept -

Lumpers: Taxonomist who propounded morpho species concept had separated some of the same species

in to two or more different species, now made biological tests to cross fertilize. Morphologically and geographically separated species have led the scientist to unify different group into single species.

For ex. varrious species of North American sparrow has been united with the multiple geographical races of song sparrow.

Note - Above definition is only applicable for sexually reproducing organism and asexually reproducing organism or for a fossil we get, could not be defined by above definition

Objection of biological species concept: Many different species could interbreed that is against Mayr's definition-

For eg.

Ø      Female lion + Male tiger > Tiglion

Ø      Male lion + Female tiger > Liger

Ø      Female Donkey + Male Horse >-Hinny

Ø      Male Donkey + Female Horse >-Mule

(D) De Candolle Definition of Species :

“Specles is a collection of individuals witch resembles with each other more than they resembles anything which can by natural fecundation produce fertile individuals and which reproduce themselves by generation such a  manner that we may form analogy  Consider that all how spring from single individuals"

Objection: Candolle tried to improve Mayor’s  definition by announcing "Produce fertile offspring and define a species as above but here are many different species that can interbreed and produce fertile offspring”.

Examples of fertile hybrid offspring –

• African lioness (Panthera leo) +Asian Tiger (Panthera tigris)- Fertile hybrid Tigon
• Mallard duck + Pintail duck - Fertile hybrid
• Polar bear + Aiaskan brown bear - Feriile hybrid
• Platy tail fish + Sward tail iish - Fertile hybrid

(E) K Jordon Definition of Species (1909) :

He define species by Behavior, Embryology, Ecology, Cytology, Biochemistry, Anatomy

(F) Modern definition of species:

(1) lt is difficult to give a definition of a species which can be applied both in plants and animals but a species may be defined as –“A population of individuals with similar structure and functional characters, which has common ancestry and In nature, breed only with each other to produces fertile offspring"

It should be noted that the phenomenon of interbreeding in species is applicable only to sexually reproducing organisms. But only criteria for identification of species in asexually reproducing organism is their physical  appearance and some characteristic proposed by K. Jordon, many species have been identified by their morphological and anatomical characters Some time such comparison are made from dead and preserved specimens placed in herbaria and museums. Thus is due to reason that to study of sexual behavior in certain organism needs much time patience and effort or some organism that never reproduce sexually

Species concept

Ø      Static species concept - Linnaeus, Aristotle, Plato

Ø      Nominalistic species concept

Ø      Biological species concept - by Mayer

Ø      Polytypic species concept - K. Jordon

(a) Static species concept :

Given by Linnaeus on the basis of external morphology like Shape,size and color-All animals that are same in shape, size, colour belongs to same specles"

Exception : ln some cases the member of a species are not morphologically similar but it cannot be said that they are different species. For eg.

(i) Ova, pupa, larva of Silk worm are not identical in morphology but it can not be said

that they are different sPecies

(ii) Pollymorphism in Termites and Honey bees

(iii) Sexual dimorphism in coelentrate like Polyp and medusa.

(iv) Sibling species that are same in shape, size, colour but can not interbreed.

(b) Nominalistic species concept:

According to this concept there is no existance of species in nature and it is (species) only imagination of human brain.

(c) Biological species concept:

"Populations of interbreeding individuals with common gene pool"

(i) lt form reproductive community

(ii) lt is an ecological unit

(iii) lt is also a genetical unit

(d) Polytypic species concept :

Type of species is determind by Behavior, Embryology, Ecology, cytology, Biochemistry

(i) lt form population that have gene pool with free gene flow

(ii)Adaptation and natural selection occur

(iii) They have power of evolution.

(iv)Eeach species has the capacity to give rise new species.

Ø      Sympatric species : The species inhabiting a same geographical area.

Ø      Allopatric species : The species inhabiting in different geographical area.

Ø      Sibling species : Group of very similar and closely related species which can not interbreed but it is difficult to separate them on the basis of morphological characters alone

Ø      Ex: Drossophila pseudobscura and D. Persimilis

Ø      Polytypic species : species which consist of two or more sub - species

                   Ex: Carvcus splendanse splendanse , Carvcus splendense isolances

(5) Monotypic species - " lt consists of single sub - species" or "species without differentiation of subspicies"

Ex: Hippopotamaus amphibicus

(6) Biological species or genetic species - there are the group of actually or potentially interbreeding natural populations which are reproductively isolated from one another

(7) Morphospecies : "These are characte,',r cy morphological resemblances only" or "species erected on ii, :is of morphological characters only"

(8) Macrospecies : A large polymarphic species rnrith several sub-divisions

Ex: Phylum chordata contain several macro species

Class mammalia contain several macro species

Order primates contain ;t ?ve[3] macrospecies

Family hominidae contain several macrospecies

(9) Microspecies : A interbreeding genetic unit below the rank of species (sub species)

Ex: Carvus splendense splendense (micro)

Carvus splendense isolances (micro)

(10) Taxonomic species : A species have definite binomial name

(11) Endemic species : Species restricted in a particular area

(12) Epidemic : Cosmopolitan species.

(13) Key stone species : The dominant species are mainaly responsible for environmental modification and alternation in community composition act as key stone species. Their critical impact on community and

environment is more important than their abundance or dominance.

Ex: Oak - Key stone species of tropical rain forest

Fig - Key stone species of temperate rain forest

Kangaroo Rat - Key stone species of desert

(14) Synchronic species : Species originated or present in same geographical time period

Ex. Dinosaur and Archaeopteryx

(15) Allochronic species : Species originated and present in different geog graphical time period

Ex : Dinusour and human

(16) Neontological species : Living or surviving species in present time.

Ex: Human, Cow, Cat, Pigeon etc.

(17) palaeospecies or Palaeontospecies: Fossil species means those species which were existing ir

ancient geographical time period but presently they are found in fossil form

Ex: Dinusour, ArchaeoPteryx, Mammoth

(18) Evolutionary Species: lt is a lineage (an ancester - descendant sequence of population) evolving separately from others and with its own unitary evolutionary role and tendencies.

Speciation

• Allopatric speciation 'When a population formerly continuous in a range , splits in to two or more geographically isolated population and form new species. Eg. Darwin finches,Marsupial radiation
• Sympatric speciation 'When a population reproductively isolated in midst of its parent population and form new species . Ex. Quated example of sympatric speciation comes from polyploidy (when chromosome fails to segregate at meiosis or replicate with out undergoing mitosis)