XSIQ
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Biology - Speciation

Speciation

If gene flow between different populations of a species becomes
interrupted, the allele frequencies in the populations may become different
enough to give rise to sub-species or races of the species. Different
selective pressures operate. This is apparent in populations of people who
are distinctly different in different parts of the world. Their differences
have been attributed to different selective pressures in their particular
habitats.

The crimson Rosella was originally classified as three distinct species
according to colour:

* the crimson Rosella;

* the Adelaide Rosella;

* the yellow Rosella.

The Rosella's are distributed differently in Australia in distinctly
different habitats (forest, woodland and river red gums respectively). The
birds between the localities were intermediate in colour and size and were
able to interbreed with the adjacent distinct populations. However, yellow
and crimson Rosellas in the same district do not inter-breed with each
other. Biologists reclassified them into the same species. Another example
of controversy over classification is that of the Australian tree creeper.

Subspecies of a species have a third part added to the scientific name of
the species for example, Homo sapiens sapiens.

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