Here's how it works in the scenario you described:
1. Geographic Isolation: The earthquake creates a physical barrier (the chasm) that prevents gene flow between the two squirrel populations. This is a classic example of allopatric speciation, where speciation occurs due to geographic separation.
2. Genetic Divergence: Over time, the two squirrel populations experience different selective pressures in their isolated environments. This could include differences in food availability, predators, or climate. These pressures favor different traits, leading to genetic changes in each population.
3. Reproductive Isolation: As the genetic differences between the two populations accumulate, they may eventually become so different that they can no longer interbreed. This is called reproductive isolation, and it marks the point at which they are considered separate species.
Examples of reproductive isolation mechanisms:
* Behavioral Isolation: The squirrels may develop different mating rituals or calls that make them incompatible.
* Temporal Isolation: The squirrels might breed at different times of the year.
* Mechanical Isolation: Physical differences in reproductive organs may prevent successful mating.
Important Note: The rate of speciation can vary depending on the size of the original population, the severity of the environmental differences, and the amount of time that passes.