Carrying capacity

Organizations: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. 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. Carrying capacity was originally used to determine the number of animals that could graze on a segment of land without destroying it. Later, the idea was expanded to more complex populations, like humans. 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 increases and death rate typically decreases. 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. A recent review finds the first use of the term in an 1845 report by the US Secretary of State to the US Senate. Several estimates of the carrying capacity have been made with a wide range of population numbers. A 2001 UN report said that two-thirds of the estimates fall in the range of 4 billion to 16 billion with unspecified standard errors, with a median of about 10 billion. More recent estimates are much lower, particularly if non-renewable resource depletion and increased consumption are considered. Changes in habitat quality or human behavior at any time might increase or reduce carrying capacity. Research conducted by the Australian National University and Stockholm Resilience Centre mentioned that there is a risk for the planet to cross the planetary thresholds and reach “Hothouse Earth” conditions.. In this case, the Earth would see its carrying capacity severely reduced. In the view of Paul and Anne Ehrlich, 'for earth as a whole (including those parts of it we call Australia and the United States), human beings are far above carrying capacity today.' 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. Supporters of the concept argue that the idea of a limited carrying capacity is just as valid 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 number of people is not the only factor in the carrying capacity of Earth. Waste and over-consumption, especially by wealthy and near-wealthy people and nations, are also putting significant strain on the environment together with human overpopulation. Population and consumption together appear to be at the core of many human problems. Some of these issues have been studied by computer simulation models such as World3. When scientists talk of global change today, they are usually referring to human-caused changes in the environment of sufficient magnitude eventually to reduce the carrying capacity of much of Earth (as opposed to local or regional areas) to support organisms, especially Homo sapiens. Some aspects of a system's carrying capacity may involve matters such as available supplies of food, water, raw materials, and/or other similar resources. In addition, there are other factors that govern carrying capacity which may be less instinctive or less intuitive in nature, such as ever-increasing and/or ever-accumulating levels of wastes, damage, and/or eradication of essential components of any complex functioning system. Eradication of, for example, large or critical portions of any complex system (envision a space vehicle, for instance, or an airplane, or an automobile, or computer code, or the body components of a living vertebrate) can interrupt essential processes and dynamics in ways that induce systems failures or unexpected collapse. (As an example of these latter factors, the 'carrying capacity' of a complex system such an airplane is more than a matter of available food, or water, or available seating, but also reflects total weight carried and presumes that its passengers do not damage, destroy, or eradicate parts, doors, windows, wings, engine parts, fuel, and oil, and so forth.) Thus, on a global scale, food and similar resources may affect planetary carrying capacity to some extent so long as Earth's human passengers do not dismantle, eradicate, or otherwise destroy critical biospheric life-support capacities for essential processes of self-maintenance, self-perpetuation, and self-repair. Thus, carrying capacity interpretations that focus solely on resource limitations alone (such as food) may neglect wider functional factors. If the humans neither gain nor lose weight in the long-term, the calculation is fairly accurate. If the quantity of food is invariably equal to the 'Y' amount, carrying capacity has been reached. Humans, with the need to enhance their reproductive success (see Richard Dawkins' The Selfish Gene), understand that food supply can vary and also that other factors in the environment can alter humans' need for food. A house, for example, might mean that one does not need to eat as much to stay warm as one otherwise would. Over time, monetary transactions have replaced barter and local production, and consequently modified local human carrying capacity. However, purchases also impact regions thousands of miles away. For example, carbon dioxide from an automobile travels to the upper atmosphere. This led Paul R. Ehrlich to develop the I = PAT equation.