Carrying capacity

It has been suggested that Optimum population be merged into this article or section. (Discuss) The carrying capacity of a biological species in an environment is the 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,1 which is different from the concept of population equilibrium. 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"2 or that it was first used during 19th Century laboratory experiments with micro-organisms.3 A recent review finds the first use of the term in an 1845 report by the US Secretary of State to the Senate.4 Contents 1 Examples 2 Mathematics 3 Humans 3.1 Food supply and consumption 3.2 Ecological footprint 4 In tourism 5 See also 6 Notes 7 References 8 External links Examples One of the world's best-studied predator-prey relationships is the moose and wolf population of Isle Royale National Park [1] in Lake Superior. Without the wolves, the moose would overgraze the island's vegetation.5 Without the moose, the wolves would die. The first scientists who studied the issue thought that the wolves would eventually overpopulate and kill all the moose calves, then die from faminecitation needed. This has not occurred as inbreeding,5 disease and environmental factors6 have limited the wolf population naturally. Easter Island has been cited as an example of a human population crash. When fewer than 100 humans first arrived, the island was covered with trees with a large variety of food types. In 1722, the island was visited by Jacob Roggeveen, who estimated a population of 2000 to 3000 inhabitants with very few trees, "a rich soil, good climate" and "all the county was under cultivation". Half a century later, it was described as "a poor land" and "largely uncultivated". The ecological collapse which followed has been variously attributed to overpopulation, slave traders, European diseases (including a smallpox epidemic which killed so many so quickly, the dead were left unburied and a tuberculosis epidemic which wiped out a quarter of the population), social upheaval and invasive species (such as the Polynesian rats which may have wiped out the ground nesting birds and eaten the palm tree seeds). Whatever the combination of factors, only 111 inhabitants were left on the island in 1877. For whatever reasons (whether Moai worship, survival, status or sheer ignorance), the question of how many humans the island could realistically support never seems to have been answered. This example, and others, are discussed at length in Jared Diamond's Collapse and subsequent literature (see Easter Island article for a thorough discussion). The Chincoteague Pony Swim [2] is a human-assisted example. Both herds are managed differently. The National Park Service owns and manages the Maryland herd while the Chincoteague Volunteer Fire Company owns and manages the Virginia herd. The Virginia herd, referred to as the "Chincoteague" ponies, is allowed to graze on Chincoteague National Wildlife Refuge, through a special use permit issued by the U.S. Fish and Wildlife Service. The size of both herds is restricted to approximately 150 adult animals each in order to protect the other natural resources of the wildlife refuge. A further example is the Island of Tarawa,7 where the finite amount of space is evident, especially since landfills cannot be dug to dispose of solid waste, due to constraints in the subsurface rock and lack of topographic elevations. With colonial influence and an abundance of food (relative to life before the year 1850), the population has expanded to the extent that overpopulation is transparently present.8 Mathematics The Lotka-Volterra equations are simple mathematical model of population dynamics which show how in a closed system, like that of the wolves and moose on Isle Royale, limited prey will cause the predator population to decline rapidly. An extended example can be used where multiple species are competing for the same resources, or single species feed on multiple prey. Humans The application 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 that it often has a blame-the-victim framework.9 Supporters of the concept argue that humans, like every species, have a finite carrying capacity. 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. Food supply and consumption Carrying capacity, at its most basic level, is about organisms and food supply, where "X" amount of humans need "Y" amount of food to survive. If the humans neither gain or lose weight in the long run, 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 Geneverification needed), 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 IPAT equation10 I = P * A * T where: I is the impact on the environment resulting from consumption P is the population number A is the consumption per capita (affluence) T is the technology factor Technology is an important factor in the dynamics of carrying capacity. For example, the Neolithic revolution increased the carrying capacity of the world relative to humans through the invention of agriculture. Currently, the use of fossil fuels has artificially increased the carrying capacity of the world by the use of stored sunlight, albeit at many other expenses. Other technological advances that have increased the carrying capacity of the world relative to humans are: polders, fertilizer, composting, greenhouses, land reclamation, and fish farming.citation needed Agricultural capability on Earth expanded in the last quarter of the 20th century. But now there are many projections of a continuation of the decline in world agricultural capability (and hence carrying capacity) which began in the 1990s. Most conspicuously, China's food production is forecast to decline by 37% by the last half of the 21st century, placing a strain on the entire carrying capacity of the world, as China's population could expand to about 1.5 billion people by the year 2050.11 This reduction in China's agricultural capability (as in other world regions) is largely due to the world water crisis and especially due to mining groundwater beyond sustainable yield, which has been happening in China since the mid-20th century.12 Ecological footprint One way to estimate human demand compared to ecosystem's carrying capacity is "Ecological Footprint" accounting. Rather than speculating about future possibilities and limitations imposed by carrying capacity constraints, Ecological Footprint accounting provides empirical, non-speculative assessments of the past. It compares historically regeneration rates (biocapacity) against historical human demand (Ecological Footprint) in the same year.1314 One result shows that humanity's demand for 1999 exceeded the planet's biocapacity for 1999 by over 20 percent.13 In tourism Main article: Tourism carrying capacity Tourism carrying capacity is a now antiquated approach to managing visitors in protected areas and national parks which evolved out of the fields of range, habitat and wildlife management. In these fields, managers attempted to determine the largest population of a particular species that could be supported by a habitat over a long period of time.15 See also Arable land Asymmetry Principle Biocapacity Ecological footprint Environmental space List of countries by fertility rate Lotka–Volterra equation Over-consumption Overpopulation Overpopulation in wild animals Population Population ecology Population growth Simon–Ehrlich wager Thomas Malthus Tourism carrying capacity Notes ^ Hui, C. (2006) Carrying capacity, population equilibrium, and envrionment's maximal load. Ecological Modelling, 192, 317-320. http://dx.doi.org/10.1016/j.ecolmodel.2005.07.001 ^ Sayre, N.F., "The Genesis, History, and Limits of Carrying Capacity", Annals of the Assoc. of American Geo., 98(1), 120-134, (2008) ^ 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) ^ Sayre, N.F., "The Genesis, History, and Limits of Carrying Capacity", Annals of the Assoc. of American Geo., 98(1), p. 122 (2008) ^ a b Vucetich, J.A., and Peterson R.O., Long-term population and predation dynamics of wolves on Isle Royale, Biology and Conservation of Wild Canids, Macdonald, D. and Sillero-Zubiri, C. (ed), OUP, 281-292, (2004) ^ Wilmers, C.C., Post, E.S., Peterson, R.O. and Vucetich, J.A., "Disease mediated switch from top-down to bottom-up control exacerbates climatic effects on moose population dynamics", Ecology Letters, 9(4), 383-389, (2006) ^ Pacific Magazine: Tarawa Tackles Growing Waste Crisis ^ Troost, J.M., The Sex Lives of Cannibals: Adrift in the Equitorial Pacific, Broadway, (2004) ^ 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) ^ Ehrlich, P.R., Holdren, J.P., "Impact of Population Growth", Science, 171(3977), 1212–1217, (1971) ^ Economy, E., China vs. Earth, The Nation, May 7, 2007 issue ^ Nielsen, R., The Little Green Handbook, Picador, (2006) ISBN 0-312-42581-3 ^ a b Wackernagel, M., Schulz, N.B., et al, “Tracking the ecological overshoot of the human economy,” Proc. Natl. Acad. Sci. USA, 99(14), 9266-9271, (2002) ^ Rees, W.E. and Wackernagel, M., Ecological Footprints and Appropriated Carrying Capacity: Measuring the Natural Capital Requirements of the Human Economy, Jansson, A., Folke, C., Hammer, M. and Costanza R. (ed.), Island Press,(1994) ^ Jurrasic Coast References Gausset Q., M. Whyte and T. Birch-Thomsen (eds.) (2005) Beyond territory and scarcity: Exploring conflicts over natural resource management. Uppsala: Nordic Africa Institute Tiffen, M, Mortimore, M, Gichuki, F. (1994) More people, less erosion: Environmental recovery in Kenya. London: Longman. Sayre, N.F. (2008) "The Genesis, History, and Limits of Carrying Capacity". Annals of the Association of American Geographers 98(1), pp. 120–134. Shelby, Bo and Thomas A. Heberlein (1986) "Carrying capacity in recreation settings." Corvallis, OR: Oregon State University Press. Karl S. Zimmer (1994) Human geography and the “new ecology”: the prospect and promise of integration. Annals of the Association of American Geographers 84, p. XXX. External links http://www.unfpa.org/public/ http://www.isleroyalewolf.org/ http://www.optimumpopulation.org http://www.DieOff.org http://www.hartford-hwp.com/archives/24/042.html http://www.carryingcapacity.org http://atlas.aaas.org/index.php?part=1&sec=trends v · d · eTopics on human population Major articles World population · Family planning · Green revolution · Overpopulation · Over-consumption (water crisis) · Reproductive rights  · Sustainable development Biological topics Population biology · Population control (one-child policy · Immigration reduction) · Population decline · Population density (physiological density) · Population growth · Population pyramid Population ecology Carrying capacity · Ecological footprint · I = P • A • T · Malthusian growth model · World3 model · Food security · World energy resources and consumption · Habitat destruction · Optimum population Literary works A Modest Proposal · An Essay on the Principle of Population · Operating Manual for Spaceship Earth · How Much Land Does a Man Need? · The Limits to Growth · The Population Bomb · The Ultimate Resource · The Skeptical Environmentalist Lists Most highly populated countries · Metropolitan areas by population Events and organizations International Conference on Population and Development  · Optimum Population Trust  · United Nations Population Fund · World Population Foundation Related articles World Population Day · "The Day of Six Billion" · Easter Island downfall · Classic Maya collapse · Holocene extinction · Fertility and intelligence  Modelling ecosystems - 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