What major factor threatens small populations by decreasing genetic diversity?

Inbreeding is a major concern for small populations because it leads to a decrease in genetic diversity. When individuals within a small population breed with one another, the likelihood of inheriting identical alleles increases. This can result in a higher probability of expressing harmful recessive traits and reducing the population's overall fitness.

Small populations have limited genetic variation, which means they lack the necessary genetic diversity required to adapt to changing environmental conditions or resist diseases. A decrease in genetic diversity can lead to inbreeding depression, where the population becomes more susceptible to extinction due to reduced reproductive success and increased vulnerability to various stressors.

While habitat destruction, global warming, and genetic drift can also impact populations, they do not directly result in the immediate decrease of genetic diversity caused by inbreeding. Habitat destruction leads to population fragmentation, which can exacerbate inbreeding as small groups become isolated. Global warming affects ecosystems and can lead to species loss, but its connection to genetic diversity is more indirect. Genetic drift affects allele frequencies in small populations, but it does so randomly and does not specifically involve mating between closely related individuals as inbreeding does.