When predation is particularly heavy, as in deer hunting, they will even overadapt and produce surplus offspring as insurance. It is a scientific fact that a pair of guppies in a tank will reproduce until they have achieved a population as large as the tank can support. Additional young will be eaten by the adults as soon as they are born. If a portion of the population is removed, subsequent young will be allowed to live until the maximum population the tank can support has again been reached. Other animals have evolved different means of controlling their numbers.
Communal birds are limited in breeding by the number of available nesting sites.
The breeding of other birds and territorial animals like wolves is limited by the amount and quality of territory open to them. Even rabbits, famous for rapid reproduction, have the ability to reabsorb embryos into their womb when conditions get crowded. The embryos of kangaroos remain in a state of arrested development in a dry season when food is scarce. In the case of the white-tailed deer, many does simply fail to ovulate when the population is above its optimum level. When the population falls below this level, however, production speeds up.