Encyclopedia of Global Resources part 37 pptx

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

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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 variation and to make genealogical connections

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 the conservation 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-speagen-cies

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 Conservaproduc-tion

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 ecology mainly

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, et al Population Genetics for Animal Conservation New York: Cambridge University

Press, 2009

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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

efits and support are 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 biogeochembiogeochem-ical

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,

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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 milmil-lion 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

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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 for useful 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 genetically modified varieties

pro-duce their own insecticide As further advances 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 largely on 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 stores and 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 terms of 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 on land 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 to groundwater, 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 vegetapreserva-tion 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

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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 of ecosystem 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 inventory and valuation of ecosystem

ser-vices, monitoring, investment in management,

educa-tion programs, and cooperaeduca-tion at all scales

A M Mannion

Further Reading

Botkin, Daniel B., and Edward A Keller Environmen-tal Science: Earth as a Living 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

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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 affect aquatic habitat for a considerable

dis-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 alterations of the phys-ical environment affect root 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 governed by 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 physichemi-cal weathering of parent material; plants are competing with one another for light, water, and

Taiga, featuring coniferous forests and located in the northern portion of the Northern Hemisphere, is one type of ecosystem (©Irina

Bekulova/Dreamstime.com)

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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 anan-other

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 or more 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

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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 formation of

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-successional conditions at the expense of

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-early-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 natural disturbance 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 to its 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 that require 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

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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 of ecosystem properties and

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

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