In biology, the carrying capacity pertains to the number of a species that an environment can sustain, considering the limiting factors at play (e.g. food, water, competition, etc.). Hui defined carrying capacity as the maximal load of a particular environment.1 McGinley also defined carrying capacity in relation to population biology. Accordingly, the carrying capacity is the population size at which the population growth rate equals zero.2 It should not be confused with the term, equilibrium population, which is defined as a population in which the gene frequencies have reached an equilibrium between mutation pressure and selection pressure.3
Food supply, water supply, habitat space, and competition with other species are some of the limiting factors affecting the carrying capacity of a given environment. But in human population, other variables such as sanitation, diseases, and medical care are also at play.
1 Hui, C (2006). "Carrying capacity, population equilibrium, and environment's maximal load".Ecological Modelling 192: 317–320.
2 McGinley, M. (2013). Carrying capacity. Retrieved from [|Link]
3 equilibrium population. (n.d.) McGraw-Hill Dictionary of Scientific & Technical Terms, 6E. (2003). Retrieved from [|Link]