evolutionary history, developmental processes, and behavioral adaptations and interactions of organisms from all over the world for the purpose of studying biodiversity. This type of study operates mainly at the levels of population, species, and communities and utilizes many subsets of ecology. Scientists employ pa- leoecology to establish historic patterns of biodiver- sity; genetic ecology, especially DNA techniques, to study variationand tomake genealogicalconnections among organisms; telemetry and satellites to study patterns in distribution of various species; and com- puter simulations and field experimentation to test out hypotheses. Both genetic and evolutionary ecol- ogy are important for theconservation of biodiversity and for developing applications to solve biological problems. Applied Ecology Ecology also involves many aspects of applied science in which the results of scientific study are applied to real-life situations, from natural resource manage- ment to urban planning. Biotic natural resources have been managed at the individual and population levels since the agricultural revolution occurred eight thousand to ten thousand years ago. Until the 1960’s, forestry, fish, and wildlife management techniques were aimed at increasing the productivity of single species—usually game species, such as quail and trout, or commercial tree species, such as loblolly pine. As community ecology and ecosystem ecology matured, and as popular concern for the loss of species arose in the 1960’s, natural resource management agen- cies began to look at the effects of single-species man- agement techniques on the entire community. Range management has always taken the community ecology perspective in managing native grass and shrub com- munities for livestock forage production. However, range conservationists also manage forage produc- tion for wildlife as well as for livestock. Conservation biology applies the understanding of all ecological levels in the attempt to prevent species extinction, to maintain species genetic diversity, and to restore self- sustaining populations of rare species or entire com- munities. Population ecology remains the core of these ap- plied ecological disciplines. Population ecologymainly deals with mortality rates, birthrates, and migration into and out of local populations. These are the biotic factors that influence population size and productiv - ity. The goal of consumptive natural resource man - agement is the harvesting of population or community productivity. The goal of nonconsumptive natural resource management is to manage for natural aes- thetic beauty, for the maintenance of diverse commu- nities, for the stability of communities and ecosystems, and for a global environment that retains regional bi- otic processes. Issues in Ecology Among the applications of ecological studies are some of the following: • climate change; and global warming; • loss of species populations and concomitant loss of biodiversity, including threatened species and endangered species (such as the collapse of bee colonies important for pollination) and the intro- duction of exotic invasive species into unnatural habitats; • changes in global ocean currents and their effect on terrestrial biomes such as forests and deserts; • human activities, including the release of pollut- ants and their impact on the food chain and animal species, and global resource consumption levels and their impact on ecosystems, land conversion and habitat loss, infrastructure development, and overexploitation; • blockage of solar energy and holes in the ozone layer; and • the potential impact of space debris on the global environment. Internationally, environmental scientists and oth- ers are entering into treaties, conducting serious dis- cussions at global conferences, and collaborating on solutions to resolve these and many other issues— including the availability of food and other re- sources—that may affect future survival. Making hu- mans aware of the many ecological concerns and gaining their support in protecting, conserving, and preserving the environment and global resources for future generations, thus enhancing the health of the Earth, may be the most important goal of the study of ecology. James F. Fowler, updated by Carol A. Rolf Further Reading Bertorelle, Giorgio, etal. PopulationGenetics for Animal Conservation. New York: Cambridge University Press, 2009. 330 • Ecology Global Resources Cain, Michael L., William D. Bowman, and Sally D. Hacker. Ecology. Sunderland, Mass.: Sinauer Associ- ates, 2008. Morin, Peter Jay. Community Ecology. 2d ed. Oxford, Oxfordshire, England: Blackwell, 2008. Sherratt, Thomas N., and David M. Wilkinson. Big Questions in Ecology and Evolution. New York:Oxford University Press, 2009. Weisman, Alan. The World Without Us. New York: Pica- dor, 2008. Web Sites Cell Press Trends in Ecology and Evolution http://www.trends.com/tree/default.htm Ecology Global Network http://ecology.com/index.php The Global Education Project http://www.theglobaleducationproject.org/earth/ global-ecology.php See also: Aggregates; Conservation biology; Deep ecology; Ecosystems; Ecozones and biogeographic realms; Fisheries; Food chain; Forest management; Overgrazing; Species loss; Wildlife; Wildlife biology. Ecosystem services Category: Ecological resources Ecosystem services are the means by which societal ben- efits and supportare provided by ecosystems. Such ben- efits and support are also known as natural capital. They include climate regulation, water availability, the maintenance of wildlife and their habitats, fodder, and the production of raw materials such as wood, fi- ber, medicines, and a range of foods. All are funda- mental components in people-environment relation- ships, given their necessity for human well-being, and all contribute to the provision and/or maintenance of global resources. Background Ecosystem services are closely linked with biogeochem- ical cycles and energy transfer. In biogeochemical cy - cles nutrients are continuously transferred between the constituent parts of the Earth’s surface: rocks, soils, water (freshwater and marine), plants, animals, and the atmosphere. These processes are vital in en- ergy transfers within food chains and webs. The spa- tial and temporal distribution of these processes is de- termined to a large extent by climatic characteristics but also influences global climate via the carbon cycle. Such processes affect the quality of the “commons” (air, water, oceans), the maintenance of which is es- sential to human well-being. These processes also control the natural capital that accrues within all eco- systems and that is used for society’s needs. Ecosystem services underpin all human activity through the con- tinuous generation of resources and the environmen- tal processes that are essential to that generation. In- evitably, ecosystem services are complex, are under pressure from a growing global population, and re- quire careful management. The Millennium Ecosystem Assessment (MEA), compiled as a collaborative effort by 1,360 scientists worldwide between 2001 and 2005, summarizes the state of and major trends in global ecosystems and their services under the four headings used below. Supporting Services The primary supporting services are nutrient cycling, soil formation, and primary production. Nutrient, or biogeochemical, cycling involves the transfer of ele- ments and compounds within and between the bio- sphere (organisms and their environment), atmo- sphere, and pedosphere (soils). They consist of pools or stores between which fluxes occur. For example, in the carbon cycle the major pools are living organisms, dead organic matter, the oceans, and the atmosphere. Fluxes occur between these pools at rates that vary ac- cording to factors such as climate. Nutrient cycles also link the inorganic and organic components of the en- vironment and operate at various spatial and tempo- ral scales. For example, photosynthesis, respiration, and decomposition link microbes, plants, and ani- mals with water, soils, and the atmosphere through carbon, hydrogen, nitrogen, phosphorus, and many other elemental cycles. Most major nutrients—carbon is the most obvious example—have a pool in the at- mosphere and are thus an influence on climate. These are gaseous biogeochemical cycles. Those nutrients without an atmospheric pool—for example, phos- phorus, iron, and calcium—are sedimentary biogeo- chemical cycles. Soil formation involves the breakdown of solid bedrock into small particles by biological, chemical, Global Resources Ecosystem services • 331 and physical processes known collectively as weather - ing. Dead organic matter from microbes, insects, and pioneer plants is mixed with the particles to create new habitats for organisms; this aids water retention, which continues the weathering process and con- tributes to the release of nutrients for use by plants. Many factors—the most important being climate— influence the processes and rates of soil formation, water availability, and degree of acidity or alkalinity. Primary production is the amount of organic mat- ter produced per unit area per unit time by organisms that can photosynthesize (green plants on land and algae in the oceans). These organisms have the ability to absorb solar energy and convert it to chemical en- ergy through the generation of complex organic com- pounds such as sugars and carbohydrates. Although less than 1 percent of the solar energy that reaches Earth is used in photosynthesis, this small amount fu- els the biosphere. Primary production is the first stage in energy transfer through ecosystems and is thus the basis of all food chains and webs. All animals, includ- ing humans, depend on primary production for sur- vival—not only for food and shelter but also for a wide range of goods, including fiber, wood, and medicine. Rates of primary production (primary productivity) are influenced by environmental factors such as water availability, annual temperature regimes, soil types, and nutrient availability. Nutrient cycling, soil forma- tion, and primary production are vital for the ecosys- tem services described below. Provisioning Services Provisioning services encompass food, wood, fiber, genetic resources, fuel, and fresh water. Primary pro- duction on land and in the oceans underpins the gen- eration and replenishment of many resources on which humanity depends. Apart from fossil fuels, these are all renewable resources and are all organic or biological in origin. The provision of fresh water is renewable but is inorganic in essence, though influ- enced by ecosystem (biological) characteristics. Global food production is a vast enterprise that es- sentially processes carbon and is a major generator of wealth. It involves crop and animal agriculture at vari- ous scales (subsistent or commercial); may have a fos- sil-fuel subsidy, as in the case of “industrialized” agri- culture; and requires a reliable supply of fresh water. An indication of the magnitude of this production is reflected in the Food and Agriculture Organization’s (FAO’s) 2006 data for the major staple crops: 695 mil - lion metric tons of maize, 634 million metric tons of rice, and 605 million metric tons of wheat. A propor- tion of this is used as animal feed to create secondary productivity such as meat and milk products. These and other crops, including cotton fiber, are produced on about 15 million square kilometers of cropland. An increasing proportion of crop production— notably that of corn, soybean, and canola—is used to generate biofuels, while several crops are grown spe- cifically as biofuels. However, the value of growing ma- terials to use as biofuels is controversial because the crops take up land that could be used for food produc- tion. An additional roughly 28 million square kilome- ters of pasture support a large proportion of the world’s cattle and sheep. Cotton is the world’s major fiber; about 25 million metric tons were produced in 2005. Fish derived from inland and marine waters form an important component of human diets. According to FAO statistics, some 141.4 million metric tons of fish were produced in 2005, about 35 percent of which was from inland waters, where aquaculture pre- dominates, and about 65 percent of which was from marine waters, where the harvesting of wild popula- tions is predominant. Some 97 percent of this is con- sumed directly by humans; the remainder is pro- cessed for animal feed. However, the global fishing industry is facing problems because fish stocks have been seriously depleted. The reduction or loss of this service illustrates the difficulties that arise when con- servation and management are inadequate: Marine ecosystems are altered and social consequences arise. The world’s natural forests and plantations are an- other major resource with a host of uses, the most im- portant of which are as materials for construction, furniture, fencing, pulp and paper, garden products, and fuel. Forests are also a source of nonwood re- sources, including nuts, berries, fodder, and game. In 2007, about 3.6 billion cubic meters of roundwood was produced globally. The chief producers were India, China, the United States, Brazil, and Canada. The proportion removed for wood fuel is unknown. However, the loss of forest cover because of agricul- ture, logging, and poor management reduces the capacity of the terrestrial biosphere to store carbon. FAO indicates that between 1990 and 2005 carbon stocks in forest biomass decreased by 1.1 billion met- ric tons of carbon annually; this reflects impairment of an ecosystem service. The organisms in the world’s ecosystems contain a 332 • Ecosystem services Global Resources wealth of genetic resources with vast potential. Biodi - versity prospecting is the term given to programs de- signed to tap this resource by identifying species and screening them foruseful properties such as crop pro- tection chemicals and pharmaceuticals.About 25 per- cent of prescription medicines are plant based, in- cluding the widely used aspirin, while the bacterium Bacillus thuringiensis is the basis of insect pest control in a range of crops. The bacterium itself is produced as a commercial spray, but the gene component re- sponsible for insect mortality has been identified and inserted into a number of crops, notably cotton and maize, so that these geneticallymodified varieties pro- duce their own insecticide. Asfurtheradvances in bio- technology and genetic modification ensue, further opportunities to harness genetic resources will arise. Fossil fuels are also generated through primary productivity but relate to geological eras many mil- lions of years in the past, when the carbon cycle in- volved the storage or sequestration of huge volumes of plant-based carbon in reservoirs that eventually be- came rocks. For example, coal formed in wetlands, and limestone formed in the oceans. These processes continue to operate but at such slow rates that fossil fuels cannot be considered renewable. Fresh water, a vital resource for human well-being, is renewable. It is a component of the hydrological cycle, a fundamental facilitating factor in ecosystem and society functioning. Water from precipitation reaches the Earth’s surface and its subsequent pas- sage depends largelyon how evaporation, recharge of groundwater reservoirs, and runoff are affected by the ecosystems through which it passes. Forest and mountain ecosystems are especially important in this context, accounting for about 85 percent of total run- off, which supports approximately 4 billion of the world’s estimated 6.7 billion people. Cultivated land accounts for most of the remainder. Wetlands are also important as water storesand hydrological regulators. Regulating Services Climate, flood, and disease regulation, water purifica- tion, and pollination are major regulating services. Climate and the Earth’s ecosystems have been inter- dependent throughout geologic time; the major link between the two is the global carbon cycle, though other biogeochemical cycles are also involved. This mutual development has manifested in various ways but is especially significant in termsof global tempera - ture regimes and atmospheric composition. The Earth and its atmosphere form a closed sys - tem, or nearly so, in terms of chemical constitution. The redistribution of atoms and molecules between the Earth’s core, lithosphere, biosphere, and atmo- sphere has been, and continues to be, mediated by life-forms onland and in the oceans.Overall, this rela- tionship has maintained life in the biosphere and helped to spur evolution. It also has caused major shifts in the carbon cycle as carbon is removed from the atmosphere into the biosphere and, eventually, the lithosphere. The evolution of photosynthesis, for example, was particularly important because it not only fixed carbon from the atmosphere but also re- leased oxygen, paving the way for the evolution of mammals, including humans. Beginning with the Industrial Revolution, humans began to alter the carbon cycle profoundly through fossil-fuel consumption and deforestation. Evidence indicates that these may contribute to global warm- ing. The speed of the alteration in the carbon cycle is more rapid than the gradual processes that charac- terize the geological past; thus, concerns about seri- ous consequences for human well-being seem to be justified. Flood regulation is a function of all ecosystems but is most important in forests, grasslands, and wetlands. Following receipt of high rainfall or snowfall such eco- systems store water in the vegetation and soils and temper its release togroundwater, streams, and rivers. This reduces the impact of floodwaters on ecosystems and society in built-up areas like river valleys, estuar- ies, and deltas. Degradation of upstream ecosystems can impair this capacity and imperils millions of peo- ple. Erosion control is also linked with the preserva- tion of an adequate vegetation cover in river catch- ments and safeguards downstream land use and settlements. The passage of water through ecosys- tems—in which vegetation, microorganisms, and soils act as filters—contributes to water purification. Pol- lutants such as metals, excess nutrients such as nitro- gen, and sediments are removed, which improves conditions for downstream ecosystems and land use. Many diseases experienced by crops and animals (including humans) are influenced by ecosystem di- versity; pest and disease outbreaks are not likely in biodiverse regions because the passage of viruses is made difficult by the buffering capacity of non-host species. The natural control of vectors is also en - hanced with high biodiversity. Pollination is another vital ecosystem service. It fa - Global Resources Ecosystem services • 333 cilitates the sexual reproduction of many plants, in - cluding crops, with genetically diverse offspring as a result. Without such fertilization, fruiting would not occur. Many animal species—bats, birds, and insects such as bees, butterflies, flies, moths, and beetles— are involved in pollination. About 33 percent of hu- man food production depends on these wild pollina- tors; thus, the service is of economic importance. Cultural Services Cultural services—aesthetic, spiritual, educational, and recreational—do not provide immediately tangi- ble resources akin to food, for example, but they con- tribute to human well-being in many ways. Further- more, in the context of education, they may improve understanding of ecosystem form and function and contribute to sustainable management strategies. Dis- tinct types ofecosystem provide a sense of place, influ- ence culture, inspire art forms, and are important in many religions. Wealth generation—through the value of landscape, wildlife, and recreation—is an- other cultural ecosystem service. Other forms of em- ployment, such as forestry, conservation, and man- agement, also contribute to wealth generation. Future Context Global population is estimated to increase to 8 billion by 2030. This will compound pressure on already stretched ecosystem services and require an increase in food production by at least 25 percent. According to the MEA, humans have altered global ecosystems more substantially since the mid-twentieth century than at any other time in history. This happened be- cause of a threefold growth in population, rapid con- version of forests and grasslands to agricultural land, technologies such as automobiles requiring fossil fu- els, and rising standards of living that encompass in- creased resource use. More than half of the services provided are being degraded mostly at the expense of the poorest people. One aspect of this degradation is the high rate of plant and animal extinction such as the loss of genetic resources, a process that, unlike many other environmental problems, is irreversible. Unsustainable practices and resulting inequity require immediate attention from local, national, and inter- national political and environmental institutions. Each requires the inventoryand valuationof ecosystem ser- vices, monitoring, investment in management, educa - tion programs, and cooperation at all scales. A. M. Mannion Further Reading Botkin, Daniel B., and Edward A. Keller. Environmen- tal Science: Earth as aLiving Planet. 7th ed.New York: John Wiley & Sons, 2009. Mannion, Antoinette M. Carbon and Its Domestication. Dordrecht, Netherlands: Springer, 2006. Melillo, Jerry, and Osvaldo Sala. “Ecosystem Ser- vices.” In Sustaining Life: How Human Health De- pends on Biodiversity, edited by Eric Chivian and Aaron Bernstein. New York: Oxford University Press, 2008. Ninan, K. N., ed. Conserving and Valuing Ecosystem Ser- vices and Biodiversity: Economic, Institutional and So- cial Challenges. Sterling, Va.: Earthscan, 2008. Web Sites Food and Agriculture Organization of the United Nations FAOSTAT http://faostat.fao.org/default.aspx Millennium Ecosystem Assessment Millennium Assessment 2009 http://www.millenniumassessment.org/en/ index.aspx See also: Agriculture industry; Biosphere; Carbon cy- cle; Ecology; Ecosystems; Ecozones and biogeo- graphic realms; Fisheries; Geochemical cycles; Green- house gases and global climate change; Hydrology and the hydrologic cycle; Natural capital; Nitrogen cycle; Phosphorus cycle. Ecosystems Category: Ecological resources An ecosystem is formed by the complex interactions of a community of individual organisms of different spe- cies with one another and with their abiotic (nonliv- ing) environment. Background A biological community consists of a mixture of popu- lations of individual species; a population consists of potentially interbreeding members of a species. Indi - vidual organisms interact with members of their own species as well as with other species. An ecosystem is 334 • Ecosystems Global Resources formed by this web of interactions among species along with the physical, chemical, and climatic condi- tions of the area. Abiotic environmental conditions include temper- ature, water availability, soil nutrient content, and many other factors that depend on the climate, soil, and geology of an area. Living organisms can alter their environment to some degree. A canopy formed by large forest trees, for example, will change the light, temperature, and moisture available to herba- ceous plants growing near the forest floor. The envi- ronmental conditions in a particular area can also be affected by the conditions of neighboring areas; the disturbance of a stream bank can lead to erosion, which will affectaquatic habitat for a considerabledis- tance downstream. It can be difficult to anticipate the wide-ranging affects of ecosystem disturbance. Species and individuals within an ecosystem may interact directly with one another through the ex - change of energy and material. Predators, for exam - ple, obtain their energy and nutritional needs through consumption of prey species. Organisms also interact indirectly through modification of their surrounding environment. Earthworms modify soil structure phys- ically, affecting aeration and the transport of water through the soil. In turn,these alterationsof thephys- ical environment affectroot growth and development as well as the ability of plants to secure nutrients. Ecosystems are not closed systems: Energy and ma- terial are transferred to and from neighboring sys- tems. The flow of energy or material between the components of an ecosystem, and exchanges with neighboring ecosystems, are governedby functions of the abiotic and biotic ecosystem components. These ecological processes operate simultaneously at many different temporal and spatial scales. At the same time that a microorganism is consuming a fallen leaf, the process of soil formation is occurring through chemi - cal and physical weathering of parent material; plants are competing with one another for light, water, and Global Resources Ecosystems • 335 Taiga, featuring coniferous forests and located in the northern portion of the Northern Hemisphere, is one type of ecosystem. (©Irina Bekulova/Dreamstime.com) nutrients; and weather may be changing—a storm front, for example, may be approaching. Ecosystem Boundaries and Temporal Scales Because of the exchange of energy and material, it is not possible to draw clear boundaries around an eco- system. A watershed is formed by topographic condi- tions forming physical barriers guiding the gravita- tional flow of water, yet wind carries seeds and pollen over these barriers, and animals can still move from watershed to watershed. The strength of the interac- tions among neighboring systems is the basis on which humans delineate ecosystem boundaries. In truth, all ecosystems around the world interact with one an- other to some degree or another. Ecological processes operate at many different timescales. Some operate over such long timescales that they are almost imperceptible to human observa- tion. The process of soil formation occurs over many human life spans. Other processes operate over ex- tremely short time intervals. The reproduction of soil bacteria, the response of leaves to changing tempera- ture over the length of a day, and the time required for chemical reactions in the soil are all very short when compared to a human life span. Usually the timescale of a process is related to its spatial scale; processes that operate at short timescales also tend to operate over short distances. Ecosystem Disturbance Ecosystems are subject to disturbance, or perturba- tion, when one ormore ecosystem processes are inter- rupted. Disturbance is a natural ecological process, and the character of many ecosystems is shaped by natural disturbance patterns. The successful repro- duction of many prairie species may be dependent on 336 • Ecosystems Global Resources Gazelles graze on an African savanna, one type of ecosystem. (©Birute Vijeikiene/Dreamstime.com) periodic fire. Suppression of fire as a means of pro - tecting an ecosystem may lead to the local extinction of small plants, which depend on periodic fires to in- crease light availability by removing larger grasses and providing nutrients to the soil. The formationof sand- bars in streams may be controlled by periodic flood events that remove great amounts of sediment from stream banks. Protection of existing ecosystems can depend on the protection or simulation of natural dis- turbances. This is even true of old-growth forests; the natural disturbance interval due to fire or windstorm may be centuries, and yet interruption of the natural disturbance pattern may lead to shifts in species com- position or productivity. Increasing the frequency of disturbance can also affect ecosystem structure and function. Repeated vegetation removal will favor species that take advan- tage of early-successionalconditions atthe expenseof species that are more adapted to late-successional conditions. In order to ensure continued functioning of ecosystem processes and the survival of all species, it is necessary to have a mix of systems in early- successional and late-successional stages in a land- scape. Human resource utilization must be managed within this context in order to ensure the long-term sustainability of all ecosystem components and to re- duce the chances of extinction of some species be- cause of human alteration of natural disturbance in- tervals. Ecosystem Stability A system is stable if it can return to its previous condi- tion at some time after disturbance. The length of time required to return to the original condition is the recovery time. Stability is an important property of ecosystems that are utilized by humans. The recov- ery of fish populations,the reestablishment of a forest following harvesting, and the renewed production of forage following grazing all depend on the inherent stability of the affected ecosystem. The stability of an ecosystem is dependent on its components and their interrelationships. Disturbance may primarily affect one component of an ecosystem, as with salmon fish- ing in the Pacific Ocean. The ability of the entire eco- system to adjust to this disturbance depends on the complexities of the interrelationships between the sal- mon, their predators and prey, and their competitors. The length of the recovery time varies with the type of system, the naturaldisturbance interval,and the se - verity of the disturbance. The population of algae along the bottom of a streambed may be severely dis - turbed by spring flooding, yet may be resilient and re- turn toits pre-disturbance condition in a short time.A forest containing one-thousand-year-old mature trees may be extremely resilient and able eventually to rees- tablish itself following a windstorm or harvesting, but the recovery time extends over many human life- times. There are species thatrequire disturbance in order to regenerate themselves. These species may be pres- ent in great abundance following a disturbance. Their abundance then decreases over time, and if there is no disturbance to renew the population, they will eventually die out and no longer be present in the ecosystem. A system is usually stable only within some bounds. If disturbed beyond these recovery limits the system may not return to its previous state but may settle into a new equilibrium. There are examples in the Medi- terranean region of systems that were overgrazed in ancient times and that have never returned to their previous species composition and productivity. Forest managers, farmers, fishermen, and others must un- derstand the natural resiliency of the systems within which they work and stay within the bounds of stability in order to ensure sustainable resource utilization into the future. Matter and Energy Cycles Ecological processes work through the cycling of mat- ter and energy within the system. Nutrient cycling consists of the uptake of nutrients from the soil and the transfer of these nutrients through plants, herbi- vores, and predators until their eventual return to the soil to begin the cycle anew. Interruption of these cy- cles can have far-reaching consequences in the sur- vival of different ecosystem components. These cycles also govern the transport and fate of toxic substances within a system. It took many years before it was real- ized that persistent pesticides such as dichloro- diphenyl-trichloroethane (DDT) would eventually be concentrated in top predators, such as raptors. The decline in populations of birds of prey because of reproductive failure caused by DDT was a conse- quence of the transport of the chemical through eco- system food webs. Likewise, radionucleides from the disaster at the Chernobyl nuclear reactor have be- come concentrated in certain components of the eco - systems where they were deposited. This is particu - larly true of fungi, which take radionucleides and Global Resources Ecosystems • 337 heavy metals from their food sources but do not shed the substances. Humans eating mushrooms from these forests can receive larger than expected doses of radi- ation, since the concentration in the fungi is much greater than in the surrounding system. A basic understanding ofecosystem propertiesand processes is critical in designing management meth- ods to allow continued human utilization of systems while sustaining ecosystem structure and function. With increasing human population and advancing liv- ing standards, more and more natural ecosystems have been pushed to near their limits of stability. It is therefore critical for humans to understand how eco- systems are structured and function in order to en- sure their sustainability in the face of continued, and often increasing, utilization. David D. Reed Further Reading Aber, John D., and Jerry M. Melillo. Terrestrial Ecosys- tems. 2d ed. San Diego, Calif.: Harcourt Academic Press, 2001. Allen, T. F. H., and Thomas W. Hoekstra. Toward a Unified Ecology. New York: Columbia University Press, 1992. Bormann, F. Herbert,and Gene E. Likens. Pattern and Process in a Forested Ecosystem: Disturbance, Develop- ment, and the Steady State Based on the Hubbard Brook Ecosystem Study. New York: Springer, 1979. Dickinson, Gordon, and Kevin Murphy. Ecosystems.2d ed. New York: Routledge, 2007. Golley, Frank Benjamin. A History of the Ecosystem Con- cept in Ecology: More than the Sum of the Parts. NewHa- ven, Conn.: Yale University Press, 1993. H. John Heinz IIICenter forScience, Economics, and the Environment. The State of the Nation’s Ecosystems 2008: Measuring the Lands, Waters, and Living Re- sources of the United States. Washington, D.C.: Island Press, 2008. Hobbs, Richard J., and Katharine N. Suding, eds. New Models for Ecosystem Dynamics and Restoration. Wash- ington, D.C.: Island Press, 2009. Schilthuizen, Menno. The Loom of Life: Unravelling Eco- systems. Berlin: Springer, 2008. Trudgill, Stephen. The Terrestrial Biosphere: Environ- mental Change, Ecosystem Science, Attitudes, and Values. New York: Prentice Hall, 2001. Williams, R.J. P., andJ. J.R. Fraústo da Silva. The Chem - istry of Evolution: The Development of Our Ecosystem. Boston: Elsevier, 2006. See also: Biodiversity; Biosphere; Carbon cycle; Con - servation; Ecology; Ecosystem services; Ecozones and biogeographic realms; Endangered Species Act; Ni- trogen cycle; Species loss; Sustainable development. Ecozones and biogeographic realms Categories: Ecological resources; environment, conservation, and resource management; plant and animal resources Ecozones and biogeographic realms are large-scale classifications that help scientists assess population sizes, histories, and locations of plant and animal spe- cies worldwide. The information aids the manage- ment and conservation of biological resources and is used to guide the choices of natural United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage sites. It also provides clues to how species evolved. Background Biogeography is the study of the distribution of living organisms in the world, past and present. “Ecozone” (short for “ecological zone”), “biogeographic realm,” “life zone,” and “biogeographic zone”are broadly syn- onymous terms for the major physical demarcations in this distribution. These terms are similar to the concept of the biome. However, whereas a biome is generally held to be a major community defined by principal vegetation and animal groups adapted to a particular environment, the ecozone takes into ac- count the geological and evolutionary history of a region. The idea for dividing the biosphere into distinct re- gions based on biological criteria dates to scientist- explorers of the eighteenth and early nineteenth cen- turies. In 1778, after sailing around the world with Captain James Cook, the English scientist J. R. Forster claimed that the world was composed of belts of simi- lar vegetation, each fostered by a distinct climate. In 1804, German scientist Alexander von Humboldt, considered by many to be the father of biogeography, built upon Forster’s conclusions to demonstrate that vegetation varied regularly in accordance with alti - tude just as it did with distance from the equator. 338 • Ecozones and biogeographic realms Global Resources Biogeographic Realms Miklos D. F. Udvardy proposed the modern biogeo- graphic realm schema in a 1975 paper, “A Classifica- tion of the Biogeographic Provinces of the World.” He defined a biogeographic realm as a continental or subcontinent region with unifying features of geogra- phy and plant and animal life. Each realm could be further divided into subrealms, or biogeographic provinces, and these into subprovinces, districts, and subdistricts, in order to define more precisely local variations in species types and distribution. Udvardy recognized eight major biogeographic realms. Each represents a region in which life-forms have adapted as a community to climatic conditions. The realms draw upon the established five classes of biomes to identify vegetation-climate interrelations: tropical humid rain forests, subtropical and temper- ate rain forests, temperate needle-leaf forests, tropical dry or deciduous forests, and temperate broad-leaf forests and subpolar deciduous thickets. TheNearctic Realm, comprising 22.9 million square kilometers of the Earth’s surface, includes most of North America. The Palearctic Realm, comprising 54.1million square kilometers, covers most of Eurasia and North Africa. The Afrotropical Realm, comprising 22.1 million square kilometers, contains sub-Saharan Africa. The Indomalayan Realm, comprising 7.5 million square kilometers, includes Afghanistan-Pakistan, South Asia, and Southeast Asia. The Oceanic Realm, comprising 1 million square kilometers, groups together Polyne- sia, Fiji, and Micronesia. The Australian Realm, which is 7.7 million square kilometers, similarly groups to- gether Australia, New Guinea, and associated islands. The Antarctic Realm, 0.3 million square kilometers, comprises the continent Antarctica. Finally, the Neo- tropical Realm, 19 million square kilometers, includes South America and the Caribbean. Ecozones Although the terms “ecozone” and “ecological zone” are used with varying meanings by others, Jürgen Schultz supplied the definitive treatment of the con- cept. In The Ecozones of the World (2005), he defines an ecozone as a large region of land where physical char- acteristics, such as climate, soil type, landscape, and geology, create a distinctive environment that sup- ports a mixture of plant life that in turn supports a mixture of animal species. As do other classification schemes, Schultz’s recognizes that vegetation is the salient feature of a region, and he organizes the eco - zones spatially by relating vegetation to climate and (as some classification schemes do not) seasonal varia- tions in climate. Schultz emphasizes that no strict bor- ders separate the ecozones; rather, they are concen- trations of highly uniform life and landscape. Shultz recognizes nine ecozones. The polar subpo- lar zone includes the areas between the North and South Poles and their respective polar tree lines, 22 million square kilometers. All of it lies within the area of permafrost; some parts are ice-covered (polar deserts), and some are tundra or bare rock. It is quite barren, characterized by very low average tempera- ture, precipitation, and biological production; ashort growing season; and low total biomass. The boreal zone, found only in the Northern Hemi- sphere, covers 20 million square kilometers and gen- erally extends from the polar tree line to the central steppes (grassy plains). It is best known as a region of coniferous forests. Most of the temperate midlatitudes zone also is lo- cated in the Northern Hemisphere—in eastern and western Eurasia and North America—although there are small areas of it in South America, Australia, and New Zealand. It includes 14.5 million square kilome- ters in narrow corridors between boreal evergreen forests and steppes. It is moderate in most of its char- acteristics, such as average temperature, precipita- tion, growing season, and total biomass. The dry midlatitudes zone occupies small areas of North America, large swaths of east-central Eurasia, the eastern part of Patagonia in South America, and part of New Zealand, for a total area of 16.5 million square kilometers. Although this zone has various subdivisions, it is arid, with at most five months of plant growth and widely dispersed plants, such as cac- tus, adapted to dry, salty soils. The subtropics with winter rain zone includes 2.5 million square kilometers, most of it along the Medi- terraneancoasts of Europe and western North Africa, but it also includes areas in southern Australia. Be- cause the Euro-African and the Australia areas are so far apart,theirplant and animal life vary considerably. The subtropics with year-round rain zone includes 6 million square kilometers total; parts of it occur in the south of the UnitedStates, southernChina, south- eastern South America, eastern South Africa, and eastern Australia. The zone sees high average temper- ature and precipitation, a long growing season, and very large biomass. The dry tropics and subtropics zone is the largest: Global Resources Ecozones and biogeographic realms • 339 . tons of carbon annually; this reflects impairment of an ecosystem service. The organisms in the world’s ecosystems contain a 332 • Ecosystem services Global Resources wealth of genetic resources. in certain components of the eco - systems where they were deposited. This is particu - larly true of fungi, which take radionucleides and Global Resources Ecosystems • 337 heavy metals from their. interactions of a community of individual organisms of different spe- cies with one another and with their abiotic (nonliv- ing) environment. Background A biological community consists of a mixture of