Speciation is the biological process which describes the creation of new species. It is known that genetics plays a large part in speciation and currently, there is debate over whether genetic drift is the largest driver in this process.
Basically there are three common models which are used to explain how speciation takes place. In these models, geographic isolation is greatly involved, along with genetic drift. Furthermore, it is important to realize that speciation is always the result of reproductive isolation.
The three models are as follows:
- Allopatric Speciation: This type of speciation occurs when there is a physical barrier which causes geographic separation (for example, habitat fragmentation) and this makes it impossible for a species to cross over to the other side. Allopatric speciation creates two separate groups which become reproductively isolated from each other. Genetic drift and natural selection play a large part in changing the allele frequencies in each of the groups over time, creating new species. Furthermore, the geography of each location may present new challenges which favour different genes. The finches observed by Charles Darwin are an example of this type of speciation.
- Parapatric Speciation: This occurs because of habitat expansion in a fairly large population. Parapatric speciation results when part of the population splits off into its own distinct group, in a new area of the pre-existing range of the total habitat.
- Sympatric Speciation: This model is largely theoretical because there isn't much evidence for it. It occurs when a population just starts to subdivide into different groups due do a certain change, such as a new food source, and is likely driven by natural selection for a specific trait. For example, the Madeiran petrel is a bird from tropical/subtropical regions, in which the same habitats house distinct populations of this species, separated by their different breeding times. Some breed during hot times and others during cold times. There is no gene flow between the hot and cold populations living on the same island, indicating reproductive isolation.