Bottleneck describes what happens to these populations genetically. Hence the correct option is d.
The term that describes what happens to populations genetically when human activities, such as overhunting and habitat destruction, lead to sudden drops in animal populations like buffalo and elephant seals is "bottleneck."
A bottleneck occurs when a population is sharply reduced in size, typically due to a dramatic event or human interference. In this scenario, the genetic diversity of the population is significantly diminished because only a small subset of individuals survive and reproduce. The surviving individuals may carry a limited set of genetic variations, leading to a reduction in allelic diversity.
As a result, the population that rebounds from the bottleneck may have lower genetic diversity compared to the original population, making it more vulnerable to diseases, environmental changes, and other challenges. The term "bottleneck" thus accurately captures the genetic consequences of human-induced population declines in species like buffalo and elephant seals. Hence the correct option is d.