Fluctuations in the , density, or of a species living in a particular area.

These fluctuations can be as occur over short, medium, or long time scales. They also can be due to versus factors impacting the population involved. Included among extrinsic factors are other species (e.g., predators or prey) and intrinsic factors include a population's maximum (i.e., ).

See, e.g., exponential growth, logistic growth, or the .