Answer:
sympatric speciation
Explanation:
Different sympatric species have the same closest ancestor and live in the same area but inhabiting different niches.
The steps for sympatric speciation are:
- An ancestral species inhabit a geographic area.
- With time, different populations of the same species occupy different niches or microhabitats in this general area.
- As the microhabitats are different, they have different environmental pressures that are acting on each population.
- These pressures lead to the origin of differences between groups, which need to adapt to each environment
- Each population suffers genetic changes due to environmental conditions. These changes are inheritable.
- With time, these differences drive to the final complete divergence of populations, becoming different species and reproductively isolated.
In sympatric speciation, the interruption of genetic flow must be fast, and there must be differences in niches so no species can compete and displace the other species. Speciation occurs in the same distribution area of the original species. The new species originate in a place with no physical barriers but different environmental pressures.
In the exposed example,
- The introduced Cichlid fishes 200 years ago → Original species and the common ancestor between the new derivated species
- The lake → general geographic area
- The main lake and the streams → Microhabitats or niches with different pressures each
- The groups are splitting into two genetically and physically different types of fishes. They do not mate. There is no genetic flow between groups. → Speciation process.