Final answer:
Inbreeding depression is the decrease in reproductive success and survival of offspring due to mating between closely related individuals. It is caused by the increased likelihood of genetic disorders and abnormalities in the offspring. This phenomenon is more common in small and isolated populations.
Step-by-step explanation:
Inbreeding depression is the reduction in reproductive success and survival of offspring resulting from mating between close relatives. When closely related individuals mate, there is an increased likelihood of genetic disorders and abnormalities in the offspring. This phenomenon is observed in small and isolated populations where there is limited genetic variation.