Answer:
The correct answer is bottleneck effect.
Explanation:
An ecosystem can change dramatically when a disaster strikes. When an event leads to a dramatic reduction in a population, it can result in a kind of genetic drift known as a bottleneck effect. A bottleneck effect can be a result of a natural calamity like a volcanic eruption or an earthquake.
When the majority of the individuals in a population die unexpectedly, genetic variation reduces and the frequencies at which distinct alleles are witnessed in the population can modify drastically. The individuals that survive were lucky as they didn't do much to survive, it was just a matter of a chance.
The surviving members do not completely demonstrate the original population, they actually under-represent or over-represent the alleles of the original population. Thus, the given case is an illustration of the bottleneck effect.
