What term describes the phenomenon when genetic diversity is reduced due to a significant drop in population size?

The term that describes the phenomenon when genetic diversity is reduced due to a significant drop in population size is known as a genetic bottleneck. This occurs when a population experiences a dramatic decline due to events such as natural disasters, habitat loss, or human activities. When the population size is severely reduced, only a small number of individuals contribute to the gene pool, which can lead to a loss of genetic variation. The surviving individuals may not represent the genetic diversity of the original population, resulting in a limited genetic foundation for future generations.

This clarifies why species that undergo a genetic bottleneck may struggle in adapting to environmental changes or diseases, as they possess a diminished set of genetic variations that could otherwise enable them to thrive under varying conditions.