Environmental Encyclopedia

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Environmental Encyclopedia 3

Ecological risk assessment

ESOURCES

OOKS

Freedman, B. Environmental Ecology, 2nd ed. San Diego: Academic

Press, 1995.

Woodley, S., J. Kay, and G. Francis, eds. Ecological Integrity and the Manage-

ment of Ecosystems. Boca Raton, FL: St. Lucie Press, 1993.

ERIODICALS

Karr, J. “Defining and assessing ecological integrity: Beyond water quality.”

Environmental Toxicology and Chemistry 12 (1993): 1521-1531.

Ecological productivity

One of the most important properties of an

ecosystem

its productivity, which is a measure of the rate of incorpora-

tion of energy by plants per unit area per unit time. In

terrestrial ecosystems, ecologists usually estimate plant pro-

duction as the total annual growth—the increase in plant

biomass

over a year. Since productivity reflects plant

growth, it is often used loosely as a measure of the organic

fertility of a given area.

The flow of energy through an ecosystem starts with

the fixation of sunlight by green plants during

photosynthe-

sis

. Photosynthesis supplies both the energy (in the form of

chemical bonds) and the organic molecules (glucose) that

plants use to make other products in a process known as

biosynthesis. During biosynthesis, glucose molecules are re-

arranged and joined together to become complex carbohy-

drates (such as cellulose and starch) and lipids (such as fats

and plant oils). These products are also combined with

nitro-

gen

phosphorus

, sulfur, and magnesium to produce the

proteins, nucleic acids, and pigments required by the plant.

The many products of biosynthesis are transported to the

leaves, flowers, and roots, where they are stored to be

used later.

Ecologists measure the results of photosynthesis as

increases in plant biomass over a given time. To do this more

accurately, ecologists distinguish two measures of assimilated

light energy: gross primary production (GPP), which is the

total light energy fixed during photosynthesis, and net pri-

mary production (NPP), which is the chemical energy that

accumulates in the plant over time.

Some of this chemical energy is lost during plant

respi-

ration

(R) when it is used for maintenance, reproduction,

and biosynthesis. The proportion of GPP that is left after

respiration is counted as net production (NPP). In an ecosys-

tem, it is the energy stored in plants from net production

that is passed up the

food chain/web

when the plants are

eaten. This energy is available to consumers either directly

as plant tissue or indirectly through animal tissue.

One measure of ecological productivity in an ecosys-

tem is the production efficiency. This is the rate of accumula-

417

tion of biomass by plants, and it is calculated as the ratio of

net primary production to gross primary production. Produc-

tion efficiency varies among plant types and among ecosys-

tems. Grassland ecosystems which are dominated by non-

woody plants are the most efficient at 60-85%, since grasses

and annuals do not maintain a high supporting biomass. On

the other end of the efficiency scale are forest ecosystems;

they are dominated by trees, and large old trees spend most of

their gross production in maintenance. For example, eastern

deciduous forests have a production efficiency of about 42%.

Ecological productivity in terrestrial ecosystems is in-

fluenced by physical factors such as temperature and rainfall.

Productivity is also affected by air and water currents,

nutri-

ent

availability, land forms, light intensity, altitude, and

depth. The most productive ecosystems are tropical rain

forests, coral reefs, salt marshes and estuaries; the least pro-

ductive are deserts,

tundra

, and the open sea. See also Eco-

logical consumers; Ecology; Habitat; Restoration ecology

[Neil Cumberlidge Ph.D.]

Ecological risk assessment

Ecological

risk assessment

is a procedure for evaluating

the likelihood that adverse ecological effects are occurring,

or may occur, in ecosystems as a result of one or more human

activities. These activities may include the alteration and

destruction of

wetlands

and other habitats, the introduction

of herbicides, pesticides, and other toxic materials into the

environment

oil spills

, or the cleanup of contaminated

hazardous waste

sites. Ecological risk assessments con-

sider many aspects of an

ecosystem

, both the biotic plants

and animals and the abiotic water, soils, and other elements.

Ecosystems can be as small as a pond or stretch of a river

or as large as thousands of square miles or lengthy coastlines

in which communities exist.

Although closely related to human health risk assess-

ment, ecological risk assessment is not only a newer discipline

but also uses different procedures, terminology, and con-

cepts. Both human health and ecological risk assessment

provide frameworks for collecting information to define a

risk and to help make risk management or regulatory deci-

sions. But human health risk assessment follows four basic

steps that were defined in a 1983 by the

National Research

Council

: hazard assessment,

dose response

assessment, ex-

posure assessment, and risk characterization. In contrast,

ecological risk assessment relies on a Framework for Ecological

Risk Assessment published by

Environmental Protection

Agency

in 1992 as part of a long-term plan to develop

ecological risk assessment guidelines. The Framework de-

fines three steps: problem formulation, analysis, and risk

characterization.

Environmental Encyclopedia 3

Ecological Society of America

The problems that human health risk assessments seek

to address are clearly defined:

cancer

birth defects

mortal-

ity

, and the like. But the problems that ecological risk assess-

ments tries to understand and deal with are less straightfor-

ward. For instance, a major challenge ecological

risk

assessors

face is distinguishing natural changes in an eco-

system from changes caused by human activities and defining

what changes are unacceptable. As a result, the initial prob-

lem formulation step of an ecological risk assessment requires

extensive discussions between risk assessors and risk manag-

ers to define “ecological significance,” a key concept in eco-

logical risk assessment. Because it is not immediately clear

whether an ecological change is positive or negative—unlike

cancer or birth defects, which are known to be adverse—

judgments must be made early in the assessment about

whether a change is significant and whether it will alter a

socially valued ecological condition. For example,

Lake Erie

was declared “dead” in the 1960s as a result of phosphorous

loadings from cities and farms. But, in fact, there were more

fish in the lake after it was “dead” than before; however,

these fish were carp, suckers, catfish, not the walleyed pike,

yellow perch, and other fish that had made Lake Erie one

of the highest valued freshwater sport fishing lakes in the

United States. More recently, with

pollution

inputs greatly

reduced, the lake has recovered much of its former productiv-

ity. Choosing one ecological condition over the other is

a social value of the kind fundamental to ecological risk

assessment problem formulation. Once judgments have been

made about what values to protect, analysis can proceed to

examine the “stressors” that ecosystems are exposed to and

a characterization can be made of the “ecological effects”

likely from such stressors.

Since 1989, EPA has held workshops on “ecological

significance” and other technical issues pertaining to ecologi-

cal risk assessment and has published the results of its work-

shops in a series of reports and case studies. In 1996, EPA

proposed its first ecological risk assessment guidelines, with

final guidelines published in May of 1998. Overall, the direc-

tion of ecological protection priorities has been away from

earlier concerns with narrow goals (e.g., use of commercially

valuable

natural resources

) toward broader interest in pro-

tecting natural areas such as National Parks and Scenic Riv-

ers for both present and

future generations

to enjoy.

[David Clarke]

ESOURCES

OOKS

Ecological Risk Assessment Issues Papers. Washington, D.C.: United States

Environmental Protection Agency, Risk Assessment Forum, 1994.

Framework for Ecological Risk Assessment. Washington, D.C.: United States

Environmental Protection Agency, Risk Assessment Forum, 1992.

418

Priorities for Ecological Protection: An Initial List and Discussion Document

for EPA. Washington, D.C. United States Environmental Protection

Agency, 1997.

ERIODICALS

Lackey, R. T. “The Future of Ecological Risk Assessment.” Human and

Ecological Risk Assessment, An International Journal 1, no. 4 (October 1995):

339-343.

Ecological Society of America

The Ecological Society of America (ESA), representing

7,500 ecological researchers in the United States, Canada,

Mexico, and 62 other countries, was founded in 1915 as a

non-profit, scientific organization and today is the nation’s

leading professional society of ecologists. Members include

ecologists from academia, government agencies, industry,

and non-profit organizations. In pursuing its goal of promot-

ing “the responsible application of ecological principles to the

solution of environmental problems,” the Society publishes

reports, membership research, and three scientific journals

a year, and it provides expert testimony to Congress. In

addition, ESA holds a conference every summer attended

by more than 3,000 scientists and students at which members

present the latest ecological research. The Society’s three

journals are: Ecology (eight issues per year), Ecological Mono-

graphs (four issues per year), and Ecological Applications (four

issues per year). ESA also publishes a bimonthly member

newsletter.

A milestone in the Society’s development was its 1991

proposal for a

Sustainable Biosphere

Initiative (SBI),

which was published in a 1991 issue of Ecology as a “call-to-

arms for ecologists.” Based on research priorities identified in

the proposal, ESA chartered the SBI Project Office in the

same year to focus on global change,

biodiversity

, and

sustainable ecosystems. The SBI marked a commitment by

the Society to more actively convey its members’ findings

to the public and to policy makers, and, as such, included

research, education, and environmental decision-making

components. The three-pronged SBI proposal grew out of

a “period of introspection” during which ESA led its mem-

bers to examine “the whole realm of ecological activities” in

the face of decreasing funds for research, an urgent need

to set priorities, and “the need to ameliorate the rapidly

deteriorating state of the

environment

and to enhance its

capacity to sustain the needs of the world’s population.”

Since the SBI Project Office was chartered, it has

focused on linking the ecological scientific community to

other scientists and decision makers through a multi-disci-

plinary 12-member Steering Committee and five-member

staff. For instance, in 1995, the SBI began a series of semi-

annual meetings with federal government officials to discuss

“overlapping areas of interest and possible collaborative op-

Environmental Encyclopedia 3

Ecological economics

portunities.” In addition, SBI has hosted discussions of key

ecological topics, such as a symposium on “ The Effects of

Fishing Activities on Benthic Habitats” that SBI and the

American Fisheries Society, the Ecological Society of

America, the

National Oceanic and Atmospheric Admin-

istration

, and the US

Geological Survey

organized in 2002

and another SBI-hosted discussion on “Ecosystem Simplifi-

cation: Why a Patchwork Quilt is More Valuable than a

Burlap Sack” at the ESA’s 2002 Annual Meeting.

In 1993 ESA chartered a Special Committee on the

Scientific Basis of

Ecosystem Management

to establish the

scientific grounds for discussing the increasingly prominent

ecosystem approach to addressing land and natural resource

management problems. The committee published its find-

ings in the August 1996 issue of Ecological Applications.

Articles discussed the emerging consensus on essential ele-

ments of ecosystem management, including its “holistic”

nature—incorporating the biological and physical elements

of an ecosystem and their interrelationships—and the con-

cept of “sustainability” as the “essential element and precon-

dition” of ecosystem management.

ESA’s headquarters in Washington, D.C., consistent

with the SBI’s goal of broader public education, includes a

Public Affairs Office. Its Publications Office is in Ithaca,

New York.

[David Clarke]

ESOURCES

ERIODICALS

“Forum: Perspectives on Ecosystem Management". Ecological Applications,

6, no. 3 (August 1996): 694–747.

“The Sustainable Biosphere Initiative: An Ecological Research Agenda".

Ecology, 72, no. 2 (1991): 371–412,

RGANIZATIONS

Ecological Society of America, 1707 H St, NW, Suite 400, Washington,

D.C. USA 20006 (202) 833-8773, Fax: (202) 833-8775, Email:

esahq@esa.org, <http://www.esa.org>

Ecological economics

Although

ecology

and economics share the common root

“eco-” (from Greek Oikos or household), these disciplines

have tended to be at odds with each other in recent years

over issues such as the feasibility of continued economic

growth and the value of

natural resources

and environmen-

tal services.

Economics deals with resource allocation or trade-offs

between competing wants and needs. Economists ask, “what

shall we produce, for whom, or for what purpose?” Further-

more, they ask, “when and in what manner should we pro-

duce these goods and services?” In mainstream, neoclassical

419

economics, these questions are usually limited to human

concerns: what will it cost to obtain the things we desire

and what benefits will we derive from them?

According to classical economists, the costs of goods

and services are determined by the interaction of supply and

demand in the marketplace. If the supply of a particular

commodity or service is high but the demand is low, the

price will be low. If the commodity is scarce but everyone

wants it, the price will be high. But high prices also encourage

invention of new technology and substitutes that can satisfy

the same demands. The cyclic relationship of scarce resources

and development of new technology or new materials, in this

view, allows for unlimited growth. And continued economic

growth is seen as the best, perhaps the only, solution to

poverty and

environmental degradation

Ecologists, however, view the world differently than

economists. From their studies of the interactions between

organisms and their

environment

, ecologists see our world

as a dynamic, but finite system that can support only a

limited number of humans with their demands for goods and

services. Many ecological processes and the nonrenewable

natural resources on which our economy is based have no

readily available substitutes. Further, much of the natural

world is being degraded or depleted at unsustainable rates.

Ecologists criticize the narrow focus of conventional eco-

nomics and its faith in unceasing growth, market valuation,

and endless substitutability. Ecologists warn that unless we

change our patterns of production and consumption to ways

that protect natural resources and ecological systems, we will

soon be in deep trouble.

Ecological economics

Ecological or

environmental economics

is a rela-

tively new field that introduces ecological understanding into

our economic discourse. It takes a transdisciplinary, holistic,

contextual, value-sensitive approach to economic planning

and resource allocation. This view recognizes our depen-

dence on the natural world and the irreplaceable life-support

services it renders. Rather than express values solely in market

prices, ecological economics pays attention to intangible val-

ues, nonmarketed resources, and the needs and rights of

future generations

and other

species

. Issues of equitable

distribution of access to resources and the goods and services

they provide need to be solved, in this perspective, by means

other than incessant growth.

Where neoclassical economics sees our environment

as simply a supply of materials, services, and waste sinks,

ecological economics regards human activities as embedded

in a global system that places limits on what we can and

cannot do. Uncertainty and dynamic change are inherent

characteristics of this complex natural system. Damage

caused by human activities may trigger sudden and irrevers-

ible changes. The precautionary principle suggests that we

Environmental Encyclopedia 3

Ecological economics

should leave a margin for error in our use of resources and

plan for

adaptive management

policies.

Natural capital

Conventional economists see wealth generated by hu-

man capital (human knowledge, experience, and enterprise)

working with manufactured capital (buildings, machines,

and infrastructure) to transform raw materials into useful

goods and services. In this view, economic growth and effi-

ciency are best accomplished, by increasing the throughput

of raw materials extracted from

nature

. Until they are trans-

formed by human activities, natural resources are regarded

as having little value. In contrast, ecological economists see

natural resources as a form of capital equally important with

human-made capital. In addition to raw materials such as

minerals, fuels, fresh water, food, and fibers, nature provides

valuable services on which we depend. Natural systems as-

similate our wastes and regulate the earth’s energy balance,

global

climate

, material

recycling

, the chemical composi-

tion of the

atmosphere

and oceans, and the maintenance

biodiversity

. Nature also provides aesthetic, spiritual,

cultural, scientific and educational opportunities that are

rarely given a monetary value but are, nevertheless, of great

significance to many of us.

Ecological economists argue that the value of natural

capital should be taken into account rather than treated as

a set of unimportant externalities. Our goal, in this view,

should be to increase our efficiency in natural resource use

and to reduce its throughput. Harvest rates for renewable

resources (those like organisms that regrow or those like

fresh water that are replenished by natural processes) should

not exceed regeneration rates. Waste emissions should not

exceed the ability of nature to assimilate or recycle those

wastes.

Nonrenewable resources

(such as minerals) may

be exploited by humans, but only at rates equal to the creation

of renewable substitutes.

Accounting for natural capital

Where neoclassical economics seeks to maximize pres-

ent value of resources, ecological economics calls for recogni-

tion of the real value of those resources in calculating eco-

nomic progress. A market economist, for example, once

argued that the most rational management policy for

whales

was to harvest all the remaining ones immediately and to

invest the proceeds in some profitable business. Whales re-

produce too slowly, he claimed, and are too dispersed to

make much money in the long run by allowing them to

remain wild. Ecologists reject this limited view of whales as

only economic units of production. They see many other

values in these wild, beautiful, sentient creatures. Further-

more whales may play important roles in marine ecology

that we don’t yet fully understand.

Ecologists are similarly critical of Gross National

Product (GNP) as a measure of national progress or well-

420

being. GNP measures only the monetary value of goods and

services produced in a national economy. It doesn’t attempt

to distinguish between economic activities that are beneficial

or harmful. People who develop

cancer

from smoking, for

instance, contribute to the GNP by running up large hospital

bills. The pain and suffering they experience doesn’t appear

on the balance sheets. When calculating GNP in conven-

tional economics, a subtraction is made, for capital deprecia-

tion in the form of wear and tear on machines, vehicles, and

buildings used in production, but no account is made for

natural resources used up or ecosystems damaged by that

same economic activity.

Robert Repeto of the

World Resources Institute

esti-

mates that

soil erosion

in Indonesia reduces the value of

crop production about 40% per year. If natural capital were

taken into account, total Indonesian GNP would be reduced

by at least 20% annually. Similarly, Costa Rica experienced

impressive increases in timber, beef, and banana production

between 1970 and 1990. But decreased natural capital during

this period represented by soil erosion, forest destruction,

biodiversity losses, and accelerated water

runoff

add up to

at least $4 billion, or about 25%, of annual GNP. Ecological

economists call for a new System of National Accounts that

recognizes the contribution of natural capital to economic

activity.

Valuation of natural capital

Ecological economics requires new tools and new ap-

proaches to represent nature in GNP. Some categories in

which natural capital might fit include:

use values: the price we pay to use or consume a resource

option value: preserving options for the future

existence value: those things we like to know still exist

even though we may never use or even see them

aesthetic value: things we appreciate for their beauty

cultural value: things important for cultural identity

scientific and educational value: information or experience-

rich aspects of nature.

How can we measure this value of natural resources

and ecological services not represented in market systems?

Ecological economists often have to resort to “shadow pric-

ing” or other indirect valuation methods for natural re-

sources. For instance, what is the worth of a day of canoeing

on a

wild river

? We might measure opportunity costs such

as how much we pay to get to the river or to rent a canoe.

The direct out-of-pocket costs might represent only a small

portion, however, of what it is really worth to participants.

Another approach is contingent valuation in which potential

resource users are asked, “how much would you be willing

to pay for this experience?” or “what price would you be

willing to accept to sell your access or forego this opportu-

nity?” These approaches are controversial because people

Environmental Encyclopedia 3

Ecology

may report what they think they ought to pay rather than

what they would really pay for these activities.

Carrying capacity and sustainable ddevelopment

Carrying capacity

is the maximum number of organ-

isms of a particular species that a given area can sustainably

support. Where neoclassical economists believe that technol-

ogy can overcome any obstacle and that human ingenuity

frees us from any constraints on population or economic

growth, ecological economists argue that nature places limits

on us just as it does on any other species.

One of the ultimate limits we face is energy. Because

of the limits of the second law of thermodynamics, whenever

work is done, some energy is converted to a lower quality,

less useful form and ultimately is emitted as waste heat. This

means that we require a constant input of external energy.

Many fossil fuel supplies are nearing exhaustion, and contin-

ued use of these sources by current technology carries untena-

ble environmental costs. Vast amounts of

solar energy

reach the earth, and this solar energy already drives the

generation of all renewable resources and ecological services.

By some calculations, humans now control or directly con-

sume about 40% of all the solar energy reaching the earth.

How much more can we monopolize for our own purposes

without seriously jeopardizing the integrity of natural sys-

tems for which there is no substitute? And even if we had

an infinite supply of clean,

renewable energy

, how much

heat can we get rid of without harming our environment?

Ecological economics urges us to restrain growth of

both human populations and the production of goods and

services in order to conserve natural resources and to protect

remaining natural areas and biodiversity. This does not nec-

essarily mean that the billion people in the world who live

in absolute poverty and cannot, on their own, meet the basic

needs for food, shelter, clothing, education, and medical care

are condemned to remain in that state. Ecological economics

calls for more efficient use of resources and more equitable

distribution of the benefits among those now living as well

as between current generations and future ones.

A mechanism for attaining this goal is

sustainable

development

, that is, a real improvement in the overall

welfare of all people on a long-term basis. In the words of

the World Commission on Economy and Development,

sustainable development means “meeting the needs of the

present without compromising the ability of future genera-

tions to meet their own needs.” This requires increased reli-

ance on renewable resources in harmony with ecological

systems in ways that do not deplete or degrade natural capital.

It doesn’t necessarily mean that all growth must cease. There

are many human attributes such as knowledge, kindness,

compassion, cooperation, and creativity that can expand infi-

nitely without damaging our environment. While ecological

economics offers a sensible framework for approaches to

421

resource use that can be in harmony with ecological systems

over the long term, it remains to be seen whether we will

be wise enough to adopt this framework before it is too late.

[William P. Cunningham Ph.D.]

ESOURCES

OOKS

Jansson, A.M., et al., eds. Investing in Natural Capital: the Ecological Econom-

ics Approach to Sustainability. Washington, D.C.: Island Press, 1994.

Krishnan, R., J.M. Harris, and N.R. Goodwin, eds. A Survey of Ecological

Economics. Washington, D.C.: Island Press, 1995.

Prugh, T. Natural Capital and Human Economic Survival. Solomons, MD:

International Society for Ecological Economics, 1995.

Turner, R.K., D. Pearce, and I. Bateman. Environmental Economics: an

Elementary Introduction. Baltimore: The Johns Hopkins University Press,

1993.

Ecological succession

see

Succession

Ecology

The word ecology was coined in 1870 by the German zoolo-

gist Ernst Haeckel from the Greek words oikos (house) and

logos (logic or knowledge) to describe the scientific study of

the relationships among organisms and their

environment

Biologists began referring to themselves as ecologists at the

end of the nineteenth century and shortly thereafter the first

ecological societies and journals appeared. Since that time

ecology has become a major branch of biological science.

The contextual, historical understanding of organisms as

well as the systems basis of ecology set it apart from the

reductionist, experimental approach prevalent in many other

areas of science.

This broad ecological view is gaining significance today

as modern resource-intensive lifestyles consume much of

nature’s supplies. Although intuitive ecology has always been

a part of some cultures, current environmental crises make

a systematic, scientific understanding of ecological principles

especially important.

For many ecologists the basic structural units of eco-

logical organization are

species

and populations. A biologi-

cal species consists of all the organisms potentially able to

interbreed under natural conditions and to produce fertile

offspring. A population consists of all the members of a

single species occupying a common geographical area at

the same time. An ecological community is composed of a

number of populations that live and interact in a specific

region.

Environmental Encyclopedia 3

Ecology

This population-community view of ecology is

grounded in natural history—the study of where and how

organisms live—and the Darwinian theory of natural selec-

tion and

evolution

. Proponents of this approach generally

view ecological systems primarily as networks of interacting

organisms. Abiotic forces such as weather, soils, and

topog-

raphy

are often regarded as external factors that influence

but are apart from the central living core of the system.

In the past three decades the emphasis on species,

populations, and communities in ecology has been replaced

by a more quantitative, thermodynamic analysis of the pro-

cesses through which energy flows and the cycling of nutri-

ents and

toxins

are carried out in ecosystems. This process-

functional approach is concerned more with the

ecosystem

as a whole than the particular species or populations that

make it up. In this perspective, both the living organisms

and the abiotic physical components of the environment are

equal members of the system.

The feeding relationships among different species in

a community are a key to understanding ecosystem function.

Who eats whom, where, how, and when determine how

energy and materials move through the system. They also

influence natural selection, evolution, and species

adapta-

tion

to a particular set of environmental conditions. Ecosys-

tems are open systems, insofar as energy and materials flow

through them. Nutrients, however, are often recycled ex-

tremely efficiently so that the annual losses to sediments or

through surface water

runoff

are relatively small in many

mature ecosystems. In undisturbed tropical rain forests, for

instance, nearly 100% of leaves and

detritus

are decomposed

and recycled within a few days after they fall to the forest

floor.

Because of thermodynamic losses every time energy is

exchanged between organisms or converted from one form

to another, an external energy source is an indispensable

component of every ecological system. Green plants capture

solar energy

through

photosynthesis

and convert it into

energy-rich organic compounds that are the basis for all

other life in the community. This energy capture is referred

to as “primary productivity.” These green plants form the

first trophic (or feeding) level of most communities.

Herbivores (animals that eat plants) make up the next

trophic level

, while carnivores (animals that eat other ani-

mals) add to the complexity and diversity of the community.

Detritivores

(such as beetles and earthworms) and

decom-

posers

(generally bacteria and

fungi

) convert dead organ-

isms or waste products to inorganic

chemicals

. The

nutrient

recycling

they perform is essential to the continuation of

life. Together, all these interacting organisms form a

food

chain/web

through which energy flows and nutrients and

toxins are recycled. Due to intrinsic inefficiencies in transfer-

ring material and energy between organisms, the energy

422

content in successive trophic levels is usually represented as

a pyramid in which primary producers form the base and

the top consumers occupy the apex.

This introduces the problem of persistent contami-

nants in the food chain. Because they tend not to be broken

and metabolized in each step in the food chain in the way

that other compounds are, persistent contaminants such as

pesticides and

heavy metals

tend to accumulate in top

carnivores, often reaching toxic levels many times higher

than original environmental concentrations. This

biomag-

nification

is an important issue in

pollution control

policies.

In many lakes and rivers, for instance, game fish have accu-

mulated dangerously high levels of

mercury

and

chlori-

nated hydrocarbons

that present a health threat to humans

and other fish-eating species.

Diversity, in ecological terms, is a measure of the num-

ber of different species in a community, while abundance is

the total number of individuals. Tropical rain forests, al-

though they occupy only about five% of the earth’s land

area, are thought to contain somewhere around half of all

terrestrial plant and animals species, while coral reefs and

estuaries are generally the most productive and diverse

aquatic communities. Community complexity refers to the

number of species at each trophic level as well as the total

number of trophic levels and ecological niches in a com-

munity.

Structure describes the patterns of organization, both

spatial and functional, in a community. In a

tropical rain

forest

, for instance, distinctly different groups of organisms

live on the surface, at mid-levels in the trees, and in the

canopy, giving the forest vertical structure. A patchy mosaic

of tree species, each of which may have a unique community

of associated animals and smaller plants living in its branches,

gives the forest horizontal structure as well.

For every physical factor in the environment there are

both maximum and minimum tolerable limits beyond which

a given species cannot survive. The factor closest to the

tolerance limit for a particular species at a particular time is

the critical factor that will determine the abundance and

distribution of that species in that ecosystem. Natural selec-

tion is the process by which environmental pressures—in-

cluding biotic factors such as predation,

competition

, and

disease, as well as physical factors such as temperature, mois-

ture,

soil

type, and space—affect survival and reproduction

of organisms. Over a very long time, given a large enough

number of organisms, natural selection works on the ran-

domly occurring variation in a population to allow evolution

of species and adaptation of the population to a particular

set of environmental conditions.

Habitat

describes the place or set of environmental

conditions in which an organism lives;

niche

describes the

role an organism plays. A yard and garden, for instance, may

Environmental Encyclopedia 3

Ecology

provide habitat for a family of cottontail rabbits. Their niche

is being primary consumers (eating vegetables and herbs).

Organisms interact within communities in many ways.

Symbiosis

is the intimate living together of two species;

commensalism

describes a relationship in which one species

benefits while the other is neither helped nor harmed.

Li-

chens

, the thin crusty plants often seen on exposed rocks,

are an obligate symbiotic association of a fungus and an alga.

Neither can survive without the other. Some orchids and

bromeliads (air plants), on the other hand, live commensally

on the branches of tropical trees. The orchid benefits by

having a place to live but the tree is neither helped nor hurt

by the presence of the orchid.

Predation—feeding on another organism—can in-

volve pathogens,

parasites

, and herbivores as well as carniv-

orous predators. Competition is another kind of antagonistic

relationship in which organisms vie for space, food, or other

resources. Predation, competition, and natural selection of-

ten lead to niche specialization and resource partitioning

that reduce competition between species. The principle of

competitive exclusion

states that no two species will remain

in direct competition for very long in the same habitat be-

cause natural selection and adaptation will cause organisms

to specialize in when, where, or how they live to minimize

conflict over resources. This can contribute to the evolution

of a given species into new forms over time.

It is also possible, on the other hand, for species to

co- evolve, meaning that each changes gradually in response

to the other to form an intimate and often highly dependent

relationship either as predator and prey or for mutual aid.

Because individuals of a particular species may be widely

dispersed in tropical forests, many plants have become de-

pendent on insects, birds, or mammals to carry pollen from

one flower to another. Some amazing examples of

coevolu-

tion

and mutual dependence have resulted.

Ecological

succession

, the process of ecosystem devel-

opment, describes the changes through which whole com-

munities progress as different species colonize an area and

change its environment. A typical successional series starts

with pioneer species such as grasses or fireweed that colonize

bare ground after a disturbance. Organic material from these

pioneers helps build soil and hold moisture, allowing shrubs

and then tree seedlings to become established. Gradual

changes in shade, temperature, nutrient availability, wind

protection, and living space favor different animal communi-

ties as one type of plant replaces its predecessors. Primary

succession starts with a previously unoccupied site. Second-

ary succession occurs on a site that has been disturbed by

external forces such as fires, storms, or humans. In many

cases, succession proceeds until a mature “climax” commu-

nity is established. Introduction of new species by natural

processes, such as opening of a land bridge, or by human

423

intervention can upset the natural relationships in a commu-

nity and cause catastrophic changes for indigenous species.

Biomes consist of broad regional groups of related

communities. Their distribution is determined primarily by

climate

, topography, and soils. Often similar niches are

occupied by different but similar species (called ecological

equivalents) in geographically separated biomes. Some of

the major biomes of the world are deserts,

grasslands

wetlands

, forests of various types, and

tundra

The relationship between diversity and

stability

ecosystems is a controversial topic in ecology. F. E. Clem-

ents, an early biogeographer, championed the concept of

climax communities: stable, predictable associations towards

which ecological systems tend to progress if allowed to follow

natural tendencies. Deciduous, broad-leaved forests are cli-

max communities in moist, temperate regions of the eastern

United States according to Clements, while grasslands are

characteristic of the dryer western plains. In this view,

ho-

meostasis

(a dynamic steady-state equilibrium), complexity,

and stability are endpoints in ecological succession. Ecologi-

cal processes, if allowed to operate without external interfer-

ence, tend to create a natural balance between organisms

and their environment.

H. A. Gleason

, another pioneer biogeographer and

contemporary of Clements, argued that ecological systems

are much more dynamic and variable than the climax theory

proposes. Gleason saw communities as temporary or even

accidental combinations of continually changing biota rather

than predictable associations. Ecosystems may or may not

be stable, balanced, and efficient; change, in this view, is

thought to be more characteristic than constancy. Diversity

may or may not be associated with stability. Some communi-

ties such as salt marshes that have only a few plant species

may be highly resilient and stable while species-rich commu-

nities such as coral reefs may be highly sensitive to distur-

bance.

Although many ecologists now tend to agree with the

process-functional view of Gleason rather than the popula-

tion-community view of Clements, some retain a belief in

the

balance of nature

and the tendency for undisturbed

ecosystems to reach an ideal state if left undisturbed. The

efficacy and ethics of human intervention in natural systems

may be interpreted very differently in these divergent under-

standings of ecology. Those who see stability and constancy

nature

often call for policies that attempt to maintain

historic conditions and associations. Those who see greater

variability and individuality in communities may favor more

activist management and be willing to accept change as

inevitable.

In spite of some uncertainty, however, about how to

explain ecological processes and the communities they create,

we have learned a great deal about the world around us

Environmental Encyclopedia 3

EcoNet

through scientific ecological studies in the past century. This

important field of study remains a crucial component in our

ability to manage resources sustainably and to avoid or repair

environmental damage caused by human actions.

[William P. Cunningham Ph.D.]

ESOURCES

OOKS

Ricklefs, R. E. Ecology. 3rd ed. New York: W. H. Freeman, 1990.

Ecology, deep

see

Deep ecology

Ecology, human

see

Human ecology

Ecology, restoration

see

Restoration ecology

Ecology, social

see

Social ecology

EcoNet

EcoNet is a computer network that focuses on environmental

topics and, through the Institute for Global Communica-

tions, has links to the international community. Several

thousand organizations and individuals have accounts on

the network. EcoNet’s electronic conferences contain press

releases, reports, and electronic discussions on hundreds of

topics, ranging from clean air to pesticides. Subscribers can

also send e-mail to other users throughout the country and

around the world. EcoNet is a branch of ICG Internet, as

are PeacNet, WomensNet, and AntiRacismNet.

ESOURCES

RGANIZATIONS

Institute for Global Communications, P.O. Box 29904, San Francisco, CA

USA 94129-0904 Email: support@igc.apc.org, <http://www.igc.org/igc/

gateway/enindex.html>

Economic growth and the

environment

The issue of economic growth and the

environment

essen-

tially concerns the kinds of pressures that economic growth,

424

at the national and international level, places on the environ-

ment over time. The relationship between

ecology

and the

economy has become increasingly significant as humans

gradually understand the impact that economic decisions

have on the sustainability and quality of the planet.

Economic growth is commonly defined as increases

in total output from new resources or better use of existing

resources; it is measured by increased real incomes per capita.

All economic growth involves transforming the natural

world, and it can effect environmental quality in one of

three ways. Environmental quality can increase with growth.

Increased incomes, for example, provide the resources for

public services such as

sanitation

and rural electricity. With

these services widely available, individuals need to worry less

about day-to-day survival and can devote more resources to

conservation

. Second, environmental quality can initially

worsen but then improve as the growth rate rises. In the

cases of

air pollution

water pollution

, and

deforestation

and encroachment there is little incentive for any individual

to invest in maintaining the quality of the environment.

These problems can only improve when countries deliber-

ately introduce long-range policies to ensure that additional

resources are devoted to dealing with them. Third, environ-

mental quality can decrease when the rate of growth in-

creases. In the cases of emissions generated by the disposal of

municipal solid waste

, for example, abatement is relatively

expensive and the costs associated with the emissions and

wastes are not perceived as high because they are often borne

by someone else.

The

World Bank

estimated that, under present pro-

ductivity trends and given projected population increases,

the output of developing countries would be about five times

higher by the year 2030 than it is today. The output of

industrial countries would rise more slowly, but it would

still triple over the same period. If environmental

pollution

were to rise at the same pace, severe environmental hardships

would occur. Tens of millions of people would become sick

or die from environmental causes, and the planet would be

significantly and irreparably harmed.

Yet economic growth and sound environmental man-

agement are not incompatible. In fact, many now believe

that they require each other. Economic growth will be under-

mined without adequate environmental safeguards, and en-

vironmental protection will fail without economic growth.

The earth’s

natural resources

place limits on eco-

nomic growth. These limits vary with the extent of resource

substitution, technical progress, and structural changes. For

example, in the late 1960s many feared that the world’s

supply of useful metals would run out. Yet, today, there is

a glut of useful metals and prices have fallen dramatically.

The demand for other natural resources such as water, how-

ever, often exceeds supply. In

arid

regions such as the Middle

Environmental Encyclopedia 3

Economic growth and the environment

East and in non-arid regions such as northern China, aqui-

fers have been depleted and rivers so extensively drained that

not only

irrigation

and agriculture are threatened but the

local ecosystems.

Some resources such as water, forests, and clean air

are under attack, while others such as metals, minerals, and

energy are not threatened. This is because the

scarcity

metals and similar resources is reflected in market prices.

Here, the forces of resource substitution, technical progress,

and structural change have a strong influence. But resources

such as water are characterized by open access, and there

are therefore no incentives to conserve. Many believe that

effective policies designed to sustain the environment are

most necessary because society must be made to take account

of the value of natural resources and governments must

create incentives to protect the environment. Economic and

political institutions have failed to provide these necessary

incentives for four separate yet interrelated reasons: 1) short

time horizons; 2) failures in property rights; 3) concentration

of economic and political power; and 4) immeasurability and

institutional uncertainty.

Although economists and environmentalists disagree

on the definition of sustainability, the essence of the idea is

that current decisions should not impair the prospects for

maintaining or improving future living standards. The eco-

nomic systems of the world should be managed so that

societies live off the dividends of the natural resources, always

maintaining and improving the asset base.

Promoting growth, alleviating poverty, and protecting

the environment may be mutually supportive objectives in

the long run, but they are not always compatible in the short

run. Poverty is a major cause of

environmental degrada-

tion

, and economic growth is thus necessary to improve the

environment. Yet, ill-managed economic growth can also

destroy the environment and further jeopardize the lives of

the poor. In many poor but still forested countries, timber

is a good short-run source of foreign exchange. When de-

mand for Indonesia’s traditional commodity export—petro-

leum—fell and its foreign exchange income slowed, Indone-

sia began depleting its hardwood forests at non-sustainable

rates in order to earn export income.

In developed countries, it is competition that can

shorten time horizons. Competitive forces in agricultural

markets, for example, induce farmers to take short-term

perspectives for financial survival. Farmers must maintain

cash flow to satisfy bankers and make a sufficient return on

their land investment. They therefore adopt high-yield

crops,

monoculture

farming, increased

fertilizer

and

pesti-

cide

use, salinizing irrigation methods, and more intensive

tillage practices which cause

erosion

“The Tragedy of the Commons” is the classic example

of property rights failure. When access to a grazing area, or

425

commons is unlimited, each herdsman knows that grass

not eaten today will not be there tomorrow. As a rational

economic being, each herdsman seeks to maximize his gain

and adds more animals to his herd. No herdsman has an

incentive to prevent his livestock from grazing the area.

Degradation follows and the loss of a common resource. In

a society without clearly defined property rights, those who

pursue their own interests ruin the public good.

In Indonesia, political upheaval can void property

rights overnight, and so any individual with a concession to

harvest trees is motivated to harvest as many and as quickly

as possible. The government-granted timber-cutting conces-

sion may belong to someone else tomorrow. The same is

true of some developed countries. For example, in Louisiana

mineral rights revert to the state when

wetlands

become

open water and there has been no mineral development on

the property. Thus, the cheapest methods of avoiding loss

of mineral revenues has been to hurry the development of oil

and gas in areas which might revert to open water, thereby,

hastening erosion and saltwater intrusion, or putting up

levies around the property to maintain it as private property,

thus interfering with normal estuarine processes.

Global or transnational problems such as

ozone layer

depletion

acid rain

produce a similar problem. Countries

have little incentive to reduce damage to the global environ-

ment unilaterally when doing so will not reduce the damag-

ing behavior of others or when reduced fossil fuel use would

leave that country at a competitive disadvantage. Interna-

tional agreements are thus needed to impose order on the

world’s nations that would be analogous to property rights.

Concentration of wealth within the industrialized

countries allows for the exploitation and destruction of eco-

systems in

less developed countries

(LDC) through, for

example, timber harvests and mineral extraction. The con-

centration of wealth inside a less developed country skews

public policy toward benefiting the wealthy and politically

powerful, often at the expense of the

ecosystem

on which

the poor depend. Local sustainability is dependent upon the

goals of those who have power—goals which may or may

not be in line with a healthy, sustainable ecosystem. Further-

more, when an exploiting party has substitute ecosystems

available, it can exploit one and then move to the next.

Japanese lumber firms harvest one country and then move

on to another. Here the benefits of sustainability are low

and exploiters have shorter time horizons than local interests.

This is also an example of how the high discount rates in

developed countries are imposed on the management of

developing countries’ assets.

Environmental policy-making is always more compli-

cated than merely measuring the effects that a proposed

policy on the environment. But because of scientific uncer-

tainty about biophysical and geological relations and a gen-

Environmental Encyclopedia 3

Ecosophy

eral inability to measure a policy’s effect on the environment,

economic rather than ecological effects are more often relied

upon to make policy. Policy-makers and institutions are

often unable to grasp the direct and indirect effects of policies

on ecological sustainability, nor do they know how their

actions will affect other areas not under their control.

Many contemporary economists and environmental-

ists argue that the value of the environment should nonethe-

less be factored into the economic policy decision-making

process. The goal is not necessarily to put monetary values

environmental resources

; it is rather to determine how

much environmental quality is being given up in the name

of economic growth, and how much growth is being given

up in the name of the environment. A danger always exists

that too much income growth may be given up in the future

because of a failure to clarify and minimize tradeoffs and to

take advantage of policies that are good for both economic

growth and the environment. See also Energy policy; Envi-

ronmental economics; Environmental policy; Environmen-

tally responsible investing; Exponential growth; Sustainable

agriculture; Sustainable biosphere; Sustainable development

[Kevin Wolf]

ESOURCES

OOKS

Farber, S. “Local and Global Incentives for Sustainability: Failures in Eco-

nomic Systems.” In Ecological Economics: The Science and Management of

Sustainability, edited by R. Constanza. New York: Columbia University

Press, 1991.

World Bank. World Development Report 1992: Development and the Environ-

ment. New York: Oxford University Press, 1992.

Ecopsychology

see

Roszak, Theodore

Ecosophy

A philosophical approach to the

environment

which em-

phasizes the importance of action and individual beliefs.

Often referred to as “ecological wisdom,” it is associated

with other

environmental ethics

, including

deep ecology

and

bioregionalism

Ecosophy originated with the Norwegian philosopher

Arne Naess. Naess described a structured form of inquiry

he called ecophilosophy, which examines

nature

and our rela-

tionship to it. He defined it as a discipline, like philosophy

itself, which is based on analytical thinking, reasoned argu-

ment, and carefully examined assumptions. Naess distin-

guished ecosophy from ecophilosophy; it is not a discipline

in the same sense but what he called a “personal philosophy,”

426

which guides our conduct toward the environment. He de-

fined ecosophy as a set of beliefs about nature and other

people which varies from one individual to another. Every-

one, in other words, has their own ecosophy, and though

our personal philosophies may share important elements,

they are based on norms and assumptions that are particular

to each of us.

Naess proposed his own ecophilosophy as a model for

individual ecosophies, emphasizing the

intrinsic value

nature and the importance of cultural and natural diversity.

Other discussions of ecosophy concentrate on similar issues.

Many environmental philosophers argue that all life has a

value that is independent of human perspectives and human

uses, and that it is not to be tampered with except for the

sake of survival. Human

population growth

threatens the

integrity of other life systems; they argue that our numbers

must be reduced substantially and that radical changes in

human values and activities are required to integrate humans

more harmoniously into the total system. See also Zero popu-

lation growth

[Gerald L. Young and Douglas Smith]

ESOURCES

OOKS

Naess, A. Ecology, Community and Lifestyle: Outline of an Ecosophy. Trans-

lated and revised by D. Rothenberg. Cambridge: Cambridge University

Press, 1989.

ERIODICALS

Hedgpeth, J. W. “Man and Nature: Controversy and Philosophy.” The

Quarterly Review of Biology 61 (March 1986): 45-67.

Ecosystem

The term ecosystem was coined in 1935 by the Oxford

ecologist Arthur Tansley to encompass the interactions

among biotic and abiotic components of the

environment

at a given site. It was defined in its presently accepted form

by Eugene Odum as follows: “Any unit that includes all of

the organisms (i.e, the community) in a given area interacting

with the physical environment so that a flow of energy leads

to clearly defined trophic structure, biotic diversity, and ma-

terial cycles (i.e., exchange of materials between living and

non-living parts) within the system.” Tansley’s concept had

been expressed earlier in 1913 by the Oxford geographer A.

J. Herbertson, who suggested the term “macroorganism” for

such a combined biotic and abiotic entity. He was, however,

too far in advance of his time and the idea was not taken

up by ecologists. On the other hand Tansley’s concept—

elaborated in terms of the transfer of energy and matter

across ecosystem boundaries–was utilized within the next