Quick questions on Speciation - TCE Biology (Tasmania)

Speciation usually follows a sequence:

Allopatric speciation happens when a physical (geographic) barrier separates populations. The barrier might be a mountain range, a river, an ocean, or new land formed by geological change. With gene flow blocked, the two populations evolve independently. This is thought to be the most common form of speciation.

Sympatric speciation happens without geographic separation, while populations still share the same area. Gene flow is interrupted by biological factors instead. Examples of how this can occur include:

Speciation does not always happen at a steady pace. Two models describe how fast it can occur. Gradualism proposes that species change slowly and steadily over very long periods, with new species emerging through the gradual accumulation of small changes. Punctuated equilibrium proposes that species stay much the same for long periods (stasis) and then change rapidly over a relatively short time, often when the environment changes quickly or a small population becomes isolated.

Once divergence begins, isolating mechanisms keep gene pools separate. They are grouped by whether they act before or after mating.