Question

What prevents speciation from occurring in sympatric populations?

Answer 1

Interbreeding.

Speciation can occur only when such interbreeding stops between two sub-populations, i.e. a natural reproductive barrier is erected.

Explanation:

Sympatric population occupies one habitat, where organisms interbreed. Thus there is no physical barrier working to separate sub-populations. As long as random interbreeding between all members continue, sympatric speciation will not occur.

Speciation in sympatric population is rare and may occur by different means: e.g.

• Habitat selection- This includes separation and mate choice preference, ultimately leading to establishment of separate sub-populations (=demes). When gene flow between these demes completely stop, speciation is achieved. This is seen in many marine fauna.

• Instantaneous genetic isolation- This is very common in plants due to appearance of polyploidy, etc. due to abnormal meiosis. Chromosome doubling in accidentally generated flora immediately establishes a new species in same habitat.