In which situation might the bottleneck effect occur?

The bottleneck effect occurs when a population's size is significantly reduced for at least one generation, leading to a loss of genetic diversity. This typically happens due to catastrophic events that drastically reduce the number of individuals in a population.

In the case of a natural disaster, such as a flood, earthquake, or wildfire, a large portion of the population may perish, leaving only a small number of survivors. The genetic makeup of the remaining individuals may not represent the genetic diversity of the original population, thus affecting future generations. This reduction in genetic diversity can hinder the population's ability to adapt to environmental changes and increase its risk of extinction.

Other options detail situations that do not lead to the bottleneck effect. For example, migration or gene flow between populations can increase genetic diversity rather than reduce it, while stable populations with normal reproductive cycles maintain genetic variance.