Which event can result in a bottleneck effect?

The bottleneck effect occurs when a population's size is significantly reduced for at least one generation, which leads to a decrease in genetic diversity. The correct choice, pertaining to individuals dying in large numbers due to a natural disaster, illustrates this phenomenon effectively. When a large proportion of a population is suddenly lost, such as during an earthquake, flood, or other catastrophic event, the surviving population may not represent the genetic diversity of the original group.

This reduction in size can lead to a limited gene pool and may result in increased inbreeding and a loss of adaptability in subsequent generations. The consequence is that the genetic make-up of the population becomes skewed, potentially making it more vulnerable to diseases or changes in the environment.

The other choices pertain to scenarios that do not produce a bottleneck effect. Migration might introduce new genes into a population, increasing genetic diversity rather than leading to a reduction. Increased gene flow between populations serves to exchange genetic material, thereby enhancing diversity. Lastly, an environmental change that favors one species might lead to competitive advantages but does not inherently reduce population size to cause a bottleneck effect. Thus, the event that results in a population bottleneck specifically is the large number of individuals dying due to a natural disaster.