What primarily affects a population after a significant founder event?

A founder event occurs when a small number of individuals from a larger population establish a new population in a different location. This event can lead to a significant reduction in genetic variation because the new population is started by only a few individuals. As a result, the genetic makeup of the new population may not represent the full diversity of the original population.

Genetic drift becomes particularly influential in this context. Since the new population is derived from a limited number of founders, random fluctuations in allele frequencies can have a large impact. Over time, certain alleles may become more or less common purely by chance rather than through selective pressures. This drift can lead to increased differences between the new population and the original population.

Natural selection can also act on a population, but its effects depend on the variation already present in the population and the selective pressures in the new environment. In the immediate aftermath of a founder event, genetic drift tends to have a more pronounced effect because the population is small and may have low genetic variability.

Disruptive selection refers to a specific type of natural selection that favors individuals at both extremes of a trait distribution, which is a more nuanced process that typically requires a relatively stable population structure and is not as directly associated with the immediate aftermath of a founder event