Final answer:
In small populations, the influence of genetic drift is more pronounced, causing a quicker decline in heterozygosity and genetic diversity. This can lead to alleles being lost more readily compared to larger populations, making small populations more vulnerable to chance events that can significantly alter their genetic structure.
Step-by-step explanation:
In a scenario with a small initial population size, we often observe that heterozygosity will decline more rapidly due to genetic drift. This phenomenon occurs because small populations are more exposed to random fluctuations in allele frequencies, leading to a reduced genetic variety. Larger populations have a more diverse gene pool, which helps buffer against these random changes.
For example, if a storm were to kill the only individuals carrying a particular allele in a small population, that allele could be lost forever, impacting the population's genetic structure. Such chance events have a more significant impact on smaller populations, while larger populations are more resistant to the random loss of alleles due to their greater number of individuals.
Genetic drift is likely to occur more rapidly on an island than on the mainland because island populations are typically smaller. Therefore, each individual's genetic contribution is more critical to the overall gene pool. Additionally, island populations often have limited opportunities for new individuals to migrate into the population, thus increasing the susceptibility to genetic drift.