A density-dependent factor is a limiting factor that depends on the population size. These factors are only effective when the population reaches a certain density. Examples of density-dependent factors include competition, parasitism, disease and predation.
Density-dependent factors have the greatest effect in large, dense populations. Where an area is overcrowded, for example, competition for food, water and sunlight is much more severe. Competition between species may lead to evolutionary changes over time.
The predator-prey relationship, predation, is one of the most well-known forms of population control.
Limiting factors are those factors that cause the population growth to stop or decrease.