Concept of Species :: essays papers

Concept of SpeciesOver the last few decades the Biological Species Concept (BSC) hasbecome predominately the dominant species definition used. This conceptdefines a species as a reproductive community.This though has had much refinement through the years. Theearliest precursor to the concept is in Du Rietz (1930), then laterDobzhansky added to this definition in 1937.But so far after this thedefinition was highly restrictive. The definition of a species that is accepted as the Biological species concept was founded by Ernst Mayr (1942) ..groups of actually or potentially interbreeding born(p)populations which atomic number 18 reproductively isolated from other such groupsHowever, this is a definition on what happens in nature. Mayrlater amended this definition to include an ecological component ..a reproductive community of populations (reproductively isolated fromothers) that occupies a specific niche in natureThe BSC is greatly accepted amongst vertebrate zoologists &entomologi sts. Two reasons account for this .Firstly these are the groupsthat the authors of the BSC worked with. (Mayr is an ornithologist &Dobzhansky has worked in the first place with Drosophila). More importantly Sexual reproduction is the predominate form of reproduction in these groups. It is not coincidental that the BSC is less widely used amongst botanists. Terrestrial plants process much more greater diversity in their mode of reproduction than vertebrates and insects.There has been many criticisms of the BSC in its theoreticalvalidity and practical utility. For example, the application of the BSC toa number of groups is problematic because of interspecific hybridisationbetween clearly delimited species.(Skelton).It cant be applied to species that reproduce asexually ( e.gBdelloid rotifers,eugelenoid flagellates ).Asexual forms of normallysexual organisms are also known. Prokaryotes are also left out by theconcept because sexuality as defined in the eukaryotesis unknown.The Biol ogical species concept is also indefinite in those landplants that primarily self-pollinate.(Cronquist 1988).Practically the BSC has its limitations in the most obvious formof fossils.-It cant be applied to this evolutionary distinct group becausethey no longer mate.( Do homo Erectus and homo sapiens represent the sameor different species?)It also has limitations when practically applied to delimitspecies. The BSC suggests breeding experiments as the test of whether a norganism is a distinct species. But this is a test rarely made, as thenumber of crosses needed to delimit a species can be massive. So the time, effort and money needed to carry out such tests is prohibitive. Not only this but the experiment carried out are often inconclusive.In practice even strong believers of the BSC use pheneticsimilarities and discontinuties for delimiting species.