Definition

A limiting factor is something that keeps a population from growing any bigger, whether too little food, water, or space, or too many predators, and it is whatever runs out first, since a plant with plenty of water and light will still stop growing if the soil lacks nitrogen; a bird that nests only in tree holes can raise only as many families as there are holes, no matter how much food is available. More formally, a limiting factor is an environmental condition or resource, biotic such as competition, predation, disease, and parasites, or abiotic such as light, water, temperature, nutrients, and space, that restricts a population's growth, abundance, or distribution; density-dependent factors like competition and disease strengthen as a population grows, while density-independent factors like floods and cold snaps hit regardless of population size, and together limiting factors set an environment's carrying capacity, with removing one factor typically just revealing the next. At the systems level, a limiting factor follows Liebig's law of the minimum, which holds that growth is controlled by the scarcest resource relative to need, and Shelford's law of tolerance, which adds that too much of a factor can limit as effectively as too little; density-dependent limitation regulates populations through negative feedback into logistic dynamics, colimitation by two resources at once is common, and identifying the limiting factor is central to agriculture, fisheries, conservation, and managing eutrophication.