Species Concept Term paper

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Over the last few decades the Biological Species Concept (BSC) has

become predominately the dominant species definition used. This concept

defines a species as a reproductive community.

This though has had much refinement through the years. The

earliest precursor to the concept is in Du Rietz (1930), then later

Dobzhansky added to this definition in 1937.But even after this the

definition was highly restrictive. The definition of a sp

ecies that is accepted as the Biological species concept was founded by

Ernst Mayr (1942);

“..groups of actually or potentially interbreeding natural

populations which are reproductively isolated from other such groups”

However, this is a definition on what happens in nature. Mayr

later amended this definition to include an ecological component;

“..a reproductive community of populations (reproductively isolated from

others) that occupies a specific niche in nature

The BSC is greatly accepted amongst vertebrate zoologists &

entomologists. Two reasons account for this .Firstly these are the groups

that the authors of the BSC worked with. (Mayr is an ornithologist &

Dobzhansky has worked mainly 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 exhibit much more greater diversity

in their mode of reproduction than

vertebrates and insects.

There has been many criticisms of the BSC in its theoretical

validity and practical utility. For example, the application of the BSC to

a number of groups is problematic because of interspecific hybridisation

between clearly delimited species.(Skelton).

It cant be applied to species that reproduce asexually ( e.g

Bdelloid rotifers,eugelenoid flagellates ).Asexual forms of normally

sexual organisms are also known. Prokaryotes are also left out by the

concept because sexuality as defined in the eukaryotes

is unknown.

The Biological species concept is also questionable in those land

plants that primarily self-pollinate.(Cronquist 1988).

Practically the BSC has its limitations in the most obvious form

of fossils.-It cant be applied to this evolutionary distinct group because

they no longer mate.( Do homo Erectus and homo sapiens represent the same

or different species?)

It also has limitations when practically applied to delimit

species. The BSC suggests breeding experiments as the test of whether a n

organism is a distinct species. But this is a test rarely made, as the

number of crosses needed to delimit a species ca

n 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 phenetic

similarities and discontinuties for delimiting species.

Although more widely known ,several alternatives to the biological

species concept exist.

The Phenetic (or Morphological / Recognition) Species Concept

proposes an alternative to the BSC (Cronquist) that has been called a

"renewed practical species definition". This defines species as;

"... the smallest groups that are consistently and persistently

distinct and distinguishable by ordinary means."

Problems with this definition can be seen ,once again depending on

the background of the user. For example "ordinary means" includes any

techniques that are widely available, cheap and relatively easy to apply.

These means will differ among different gr

oups of organisms. For example, to a botanist working with angiosperms

ordinary means might mean a hand lens; to an entomologist working with

beetles it might mean a dissecting microscope; to a phycologist working

with diatoms it might mean a scanning electron microscope. What means are

ordinary are determined by what is needed to examine the organisms in

question.

So once again we see that it is a Subjective view depending on how

the biologist wants to read the definition. It also has similar

difficulties to the BSC in defining between asexual species and existence

of hybrids.

There are several phylogenetic species...

You should cite this paper as follows:

MLA Style
. EssayMania.com. Retrieved on 25 May, 2012 from
    <http://essaymania.com/415/species-concept>

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