The carrying capacity of an environment is the maximum population size of a species that the environment can support sustainably over a long period of time.When a population grows, resources such as food, water, shelter and space eventually become limited. Competition increases, and predation and disease become more common as individuals live closer together. The death rate rises (and the birth rate may fall) until they are equal. The population then stops growing and levels off at the carrying capacity, which is the stationary phase of the growth curve.
In reality, a population does not stay exactly at the carrying capacity. It fluctuates around it:• if the population rises above the carrying capacity, resources become too scarce, so deaths increase and the population falls
• if the population falls below it, resources become more available, so births exceed deaths and the population rises again.The carrying capacity is not fixed. It is set by limiting factors, and changes if they change. For example, a mild winter, an increase in food supply or the removal of a predator can raise the carrying capacity, while a drought, habitat loss or the arrival of a new competitor can lower it.Example: if an island's vegetation can feed about 300 deer, the carrying capacity is about 300. If a fire destroys half the vegetation, the carrying capacity falls to roughly 150 and the deer population declines towards that level.
In reality, a population does not stay exactly at the carrying capacity. It fluctuates around it:• if the population rises above the carrying capacity, resources become too scarce, so deaths increase and the population falls• if the population falls below it, resources become more available, so births exceed deaths and the population rises again.The carrying capacity is not fixed. It is set by limiting factors, and changes if they change. For example, a mild winter, an increase in food supply or the removal of a predator can raise the carrying capacity, while a drought, habitat loss or the arrival of a new competitor can lower it.Example: if an island's vegetation can feed about 300 deer, the carrying capacity is about 300. If a fire destroys half the vegetation, the carrying capacity falls to roughly 150 and the deer population declines towards that level.