Regulating factors
（重定向自Regulating factor）
In population ecology, a regulating factor is something that keeps a population at equilibrium (neither increasing nor decreasing in size over time).
An example of a regulating factor would be food supply. If the population increases to a certain size, there will be less food for each organism. This will lead to fewer births (a decrease in fecundity) and more deaths, making a negative growth rate. As there are now fewer animals, the amount of food for each organism will increase, meaning the growth rate will become positive. This would lead to a large population size again, and the cycle would start over. Therefore, food is a regulating factor in this scenario, as food supply keeps the population at relative equilibrium.