There are several factors affecting populations of wildlife.
All life needs food, cover, water and space to survive.
A species' habitat is an area that provides food, cover and water in the appropriate forms, proportion and arrangement for that species' adaptations. The physical space required by an individual animal of a species is affected by amount of food, cover and water present. The maximum number of individuals of a species that can be supported by an ecosystem over time is called its carrying capacity. It is a function of the quantity, quality, distribution and seasonal variation of food, water and cover in the ecosystem. When the carrying capacity of a species' habitat is high, but the population there is low, the number of live births per female per year is high.