Normally in nature populations are controlled by multiple limiting factors so that populations do not get out of control. There are two main kinds of limiting factors that do this; density-dependent and density-independent. Density-dependent limiting factors are those that affect a population when the population becomes large. They cause the reproductive rates to decrease, mortality rates to increase, or both. This is often because populations reach their carrying capacity and the environments can no longer support any larger of a population. Density-independent limiting factors cause changes in the population that do not go along with the logistic growth pattern of density-dependence. These are usually things that come from outside of the environment. This can be things like extreme seasons, drought, or natural disasters, which reduce a population.