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The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. In population biology, carrying capacity is defined as the environment's maximal load, which is different from the concept of population equilibrium. Its effect on population dynamics may be approximated in a logistic model, although this simplification ignores the possibility of overshoot which real systems may exhibit. For the human population, more complex variables such as sanitation and medical care are sometimes considered as part of the necessary establishment. As population density increases, birth rate often decreases and death rate typically increases. The difference between the birth rate and the death rate is the "natural increase". The carrying capacity could support a positive natural increase, or could require a negative natural increase. Thus, the carrying capacity is the number of individuals an environment can support without significant negative impacts to the given organism and its environment. Below carrying capacity, populations typically increase, while above, they typically decrease. A factor that keeps population size at equilibrium is known as a regulating factor. Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight. The carrying capacity of an environment may vary for different species and may change over time due to a variety of factors, including: food availability, water supply, environmental conditions and living space. The origins of the term "carrying capacity" are uncertain, with researchers variously stating that it was used "in the context of international shipping" or that it was first used during 19th-century laboratory experiments with micro-organisms.〔Zimmerer, K.S., ("Human Geography and the "New Ecology": The Prospect of Promise and Integration" ), ''Annals of the Assoc. of American Geo.'', 84(1), 108–125, (1994)〕 A recent review finds the first use of the term in an 1845 report by the US Secretary of State to the Senate.〔 ==Humans== (詳細はresource depletion and increased consumption are considered. The application of the concept of carrying capacity for the human population has been criticized for not successfully capturing the multi-layered processes between humans and the environment, which have a nature of fluidity and non-equilibrium, and for sometimes being employed in a blame-the-victim framework.〔Cliggett, L., "Carrying Capacity's New Guise: Folk Models for Public Debate and Longitudinal Study of Environmental Change", ''Africa Today'', 48(1), 2-19, (2001)〕 Supporters of the concept argue that the idea of a finite carrying capacity is just as valid when applied to humans as when applied to any other species. Animal population size, living standards, and resource depletion vary, but the concept of carrying capacity still applies. The carrying capacity of Earth has been studied by computer simulation models like World3. Numbers of people are not the only factor. Waste and over-consumption, especially by wealthy people and nations, is putting more strain on the environment than overpopulation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carrying capacity」の詳細全文を読む スポンサード リンク
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