Question

a female rabbit can give birth to over 40 baby rabbits a year. suppose all of her offspring survived and reproduced, and so on. if that happened, the mass of rabbits would exceed the mass of earth! so, why arent we overrun with rabbits? what keeps the rabbit population in check?

Explanation:

There are multiple factors that keep rabbit populations in check. Predation by animals like foxes, wolves, and birds - of - prey reduces their numbers. Limited food resources such as grass, herbs, and vegetables can't support an unlimited population. Diseases and parasites also play a role in controlling rabbit populations. Competition for space and mates within the rabbit population itself can limit growth.

Answer:

Predation, limited food resources, diseases/parasites, and competition for space/mates keep the rabbit population in check.