7.10 Speciation

Describe the conditions under which new species may arise.

• Speciation occurs when two populations become reproductively isolated from each other.
• The biological species concept provides a commonly used definition of a species for sexually reproducing organisms. It states that species can be defined as a group capable of interbreeding and exchanging genetic information to produce viable, fertile offspring.

Describe the rate of evolution and speciation under different ecological conditions.

• Punctuated equilibrium is when evolution occurs rapidly after a long period of stasis. Gradualism is when evolution occurs slowly over hundreds of thousands or millions of years.
• Divergent evolution occurs when adaptation to new habitats results in phenotypic diversification. Speciation rates can be especially rapid during times of adaptive radiation as new habitats become available.
• Convergent evolution occurs when similar selective pressures result in similar phenotypic adaptations in different populations or species.

Explain the processes and mechanisms that drive speciation.

• Sympatric speciation occurs in populations with geographic overlap. Allopatric speciation occurs in populations that are geographically isolated.
• Various pre-zygotic and post-zygotic mechanisms can maintain reproductive isolation and prevent gene flow between populations.