Final answer:
The bottleneck effect is when a sudden environmental change like a fire or flood drastically reduces a population's size and causes a change in its genetic structure.
Step-by-step explanation:
The event described, such as a fire, flood, or other natural disaster that drastically reduces the size of a population, is known as the bottleneck effect. This phenomenon occurs when there is a sudden change in the environment that causes a significant decrease in a population's size, resulting in a loss of genetic diversity as the genetic structure of the surviving population becomes different from the original population. It is particularly pronounced in small, isolated populations that are more vulnerable to such environmental disturbances.
Examples of events that can cause a bottleneck effect include wildfires, volcanic eruptions, earthquakes, and hurricanes. These environmental disturbances can lead to a dramatic shift in the population's genetic make-up and potentially impact its long-term survival and evolution.