Question

Compare and contrast the mechanisms of how populations evolve over time. Discuss how new species can evolve with an emphasis on allopatric speciation. Be sure to define all terms you use

Answer 1

Speciation is the evolutionary process by which populations evolve to become new species. There are four modes of geographic speciation in nature:

• Allopatric speciation: In this kind of speciation, a population splits into two geographically isolated populations. When the populations come back into contact, they become reproductively isolated and are no longer capable of exchanging genes.
• Peripatric speciation: It is a subform of allopatric speciation. new species are formed in small isolated populations that are prevented from exchanging genes with the main population. Genetic drift plays a very important role in this regard.
• Parapatric speciation: Speciation in which there is partial separation of zones of two diverging populations. They may come in contact or cross habitats from time to time. But, the fitness of the population is reduced considerably; so this prevents interbreeding.
• Sympatric speciation:It is the formationof two or more descendant species from a single ancestral species which occupies the same geographic location.

They can be tabulated as under:

Allopatric Speciation	Peripatric Speciation	Parapatric speciation	Sympatric Speciation
The first step in species formation involves the formation of barriers,	It results as a population enters a new niche.	Same as peripatric speciation.	This results out of genetic polymorphism.
The reproductive isolation takes place within.	It takes place in the niche which becomes reproductively isolated.	It takes place in adjacent niche.	The isolation occurs within the population.

For allopatric speciation, the geographically isolated populations undergo divergence in genotypic or phenotypic arrangements. This happens due to the influence of selective pressures,genetic drift, occurence of mutations in the populations Genetic drift is the variation in the relative frequency of different genotypes in a population; here particular genes tend to disappear as individuals die or do not reproduce . When they come back into contact, they become reproductively isolated and hence cannot interbreed among themselves and thus leads to speciation. Examples include Finches of Galapagos Islands.