Encyclopedia of Global Resources part 28 doc

During the Great Depression of the 1930’s, the Franklin Delano Roosevelt administration instituted a number of programs in the United States that ad-dressed natural resource problems and

Trang 1

The planet Earth may be unable to support future

in-creases in population unless, on a worldwide scale,

humans begin to conserve and reduce their rates of

consumption and increase efforts to recycle resources

for new uses Moreover, the current global economy is

no longer sustainable and is destroying the

environ-ment and providing little to support the globally

im-poverished Internationally, governments and social

activists have begun to work together to establish

poli-cies that protect the environment and the

sustain-ability of life while concomitantly fostering

harmoni-ous economic growth

“Conservation” generally refers to the use of

re-sources found in the natural environment in such a

way that the resources will serve humans effectively

and will be available to humans for as long as possible

Therefore, it does not refer to the indefinite

“preser-vation” of resources in their natural state

Quantita-tively, effective conservation could be said to involve

obtaining the maximum use for the maximum

num-ber of people

The Earth can be viewed as a life-support system

composed of four major subsystems through which

energy flows and matter cycles The subsystems are

the atmosphere, biosphere, lithosphere, and

hydro-sphere, referring to gases, life systems, rock and

min-eral materials, and water, respectively As energy flows

and matter cycles within and among these subsystems,

they interact as component parts to compose the

Earth’s ecosystem (an ecosystem may be defined as a

community of plants, animals, and other organisms

interacting in an environment) Humans alter the

natural cycling of energy and flow of matter in the

Earth’s ecosystem We extract things from natural

systems, convert them into what we perceive as more

useful products, and then return them to the natural

environment in different forms and physical states

In order to achieve more desirable energy

conver-sions, we also use energy from the environment

Natu-ral resources are all of the things that humans take

from the environment to help satisfy their needs and

wants

Resources and Reserves

All the matter and energy on Earth make up its

“stock.” Natural resources are subsets of this stock that

help humans meet their energy and material needs

Those natural resources that are available in a usable

form and at an affordable price under prevailing

tech-nology and socioeconomic conditions make up “re-serves.” For example, uranium was not a part of hu-man energy reserves until the technology to capture and control the flow of nuclear energy was developed Agrofuels produced from plant resources and biofuels developed from recently lifeless plant and an-imal materials are other examples of the marriage be-tween natural resources and technology to meet en-ergy demands for such uses as powering vehicles and heating buildings

Natural resources may be classified as renewable, nonrenewable, and perpetual Renewable resources are those that can be reproduced at a rate equal to or greater than the rate of consumption Renewable re-sources are replenished through natural, physical, and biogeochemical cycles Examples of renewable resources are forest and soil They are conserved when they are used and reused at a rate, and in such a way, that does not destroy their sustainability This does not mean that they cannot be depleted; it means that the rate of consumption does not exceed the rate at which they are replenished over an extended period

Nonrenewable resources, on the other hand, are those for which the rate of consumption exceeds the rate of renewal They are exhaustible, cannot be re-plenished, and exist in fixed amounts Nonrenewable resources, such as minerals and fossil fuels, are con-served by more thorough exploitation of their depos-its and more efficient use Some can be recycled or reused Recycling involves collecting and reprocess-ing a resource, while reuse involves usreprocess-ing a resource again in the same form The reprocessing of used alu-minum cans into new cans is an example of recycling Washing beverage bottles before using them again is

an example of reuse Other nonrenewable resources, such as coal and oil, are gone forever once they are used

Perpetual resources, such as water, wind, tides, and solar energy, continue to flow throughout the Earth’s ecosystem whether humans use them or not There-fore, they are sometimes called flow resources Even when their quality is altered they generally continue

to flow within the Earth’s ecosystem, making them in-exhaustible However, man is affecting the flow of some of these resources, such as water, and the recent harnessing of wind resources to produce energy is leading some scientists to suggest that altering the flow of wind with multiple, large turbines may lead to climate change

Trang 2

Conservation vs Preservation

“Conser vation” of natural resources

means using things found in the natural

environment wisely In a more quantitative

sense, it means sustainability of the natural

resources by obtaining the maximum use

for the maximum number of people

with-out compromising future needs It does

not imply that resources should be entirely

preserved for use later; rather, it means

that they should be employed in a way that

serves humans as well and as long as

possi-ble Although preservation is closely

asso-ciated with some aspects of conservation,

the two approaches are different, as

“pres-ervation” means the complete protection

of natural resources from human

distur-bance It is true that to conserve some

re-sources is to preserve them: We conserve

natural resources such as ecosystems, for

example, by restricting their use and

pro-tecting them from being altered, because

their value is diminished if they are not

re-tained in their original state However, we

conserve most resources when we use

them in a certain way, not when we leave

them idle

Historical Perspective

Not until technology developed

signifi-cantly, and the world’s human population

reached a certain size, did human

exploi-tation of the environment begin to have

significant effects Until that time,

conser-vation of resources was simply not an issue

For most of humankind’s existence,

peo-ple lived a simpeo-ple hunter-gatherer

exis-tence, obtaining just enough food to

survive Most people lived in small groups—fifty or

fewer people—that had little effect on resources or

the environment They made simple tools and

weap-ons Many groups were nomadic, migrating with the

seasons and following game animals The shift from a

hunting-and-gathering society to a sedentary one

be-gan about ten thousand years ago People bebe-gan

breeding animals and cultivating wild plants, thereby

having a greater impact on the environment

Slash-and-burn cultivation involved cutting down trees and

other vegetation, leaving the cut vegetation on the

ground to dry, and then burning it to enrich the soil

Farmers were “subsistence farmers,” producing only enough to feed their families

With the invention of the metal plow about seven thousand years ago, agriculture could be practiced on

a larger scale Animals were used to pull the plows, in-creasing crop productivity and making the cultivation

of new soils possible Forests were cut and grasslands were plowed—soil erosion and degradation of wild-life habitats inevitably began to follow on a small scale Occasional food surpluses were produced for sale or storage Surpluses allowed the development of urban cultures by releasing people from the farm By the

A primary concern of the modern environmental movement is the abandonment of polluting fuels In 2009, these protesters called for the plant that provides power to the U.S Capitol to cease its practice of burning coal for electricity (Roger L.

Wollenberg/UPI/Landov)

Trang 3

nineteenth century, urbanization and the Industrial

Revolution were having profound impacts on the

en-vironment and the rate of resource consumption

History of the Conservation Movement

In 1864, George Perkins Marsh published Man and

Nature: Or, Physical Geography as Modified by Human

Ac-tions Marsh’s book, which claimed that humanity

could no longer afford to continue wastefully

exploit-ing natural resources, is thought by some to mark the

beginning of the conservation movement However,

American Indians must also be given credit as one of

the first peoples to practice sustainable natural

re-source use In 1878, John Wesley Powell completed A

Report on the Lands of the Arid Region of the United States.

Powell’s study of the geomorphology and arid

land-scape transformations in the Colorado River basin

was grounded in scientific methodology and called

for the creation of a federal agency to survey and map

all U.S lands In 1879, the United States Geological

Survey was created for this purpose At the beginning

of the twentieth century there was growing concern

that resource mismanagement could have tragic

fu-ture consequences These concerns were based on

sci-entific findings associated with the exploitation and

depletion of timber In 1907, the Inland Waterways

Commission, headed by U.S Forest Service chief

Gifford Pinchot, reported that the use and control of

water would have an impact on other resources,

in-cluding timber, soil, wildlife, and minerals Pinchot’s

views on resource management greatly influenced

forest and water management policies in the United

States

During the Great Depression of the 1930’s, the

Franklin Delano Roosevelt administration instituted

a number of programs in the United States that

ad-dressed natural resource problems and helped create

employment In the wake of the severe drought and

wind erosion in the Dust Bowl, the Public Works

Ad-ministration initiated the Prairie States Forestry

Proj-ect Its goal was to establish a shelter belt of trees and

shrubs from the Texas panhandle to the Canadian

border in North Dakota This project was designed to

reduce wind erosion on rangeland and cropland

Other efforts included the creation of the Tennessee

Valley Authority (TVA) and the Civilian Conservation

Corps (CCC) The TVA was an innovative water

re-source management program that involved

compre-hensive regional planning Though confined to the

Tennessee River and its tributaries, it provided a model

for total resource management The aim of the CCC was to provide employment while repairing some of the damage that had resulted from past exploitation

of natural resources and neglect of the environment Workers constructed bridges, roads, and fire lanes for the development of recreational facilities; con-ducted tree-planting programs; instituted soil- and water-erosion control projects; made lake and stream improvements; and participated in flood control proj-ects

Many of these early conservation practices in the United States spread to other countries and, over time, several international conservation organizations were formed, including the United Nations Envi-ronment Programme, the International Union for the Conservation of Nature, and the World Wild-life Fund After World War II, nations focused on resource-related problems, many times creating agen-cies to assess the impact that the war had on forest and natural resources Moreover, the use of atomic bombs

in the war—and the widespread nuclear testing that occurred in the 1950’s—exposed ecosystems to signif-icant levels of radiation This situation marked the beginning of the modern conservation movement

The Modern Conservation Movement Although the United States is credited as the front-runner of the early conservation movement through its linking of ecology with conservation and resource management practices on public lands, during the modern conservation movement, especially in the 1980’s, the United States focused on economic growth and deregulation, sacrificing conservation Neverthe-less, the efforts of the Worldwatch Institute and older organizations such as the Sierra Club, the Audubon Society, and Friends of the Earth kept the general citi-zenry aware of environmental and resource-related issues and their consequences

In 1962, Rachel Carson, in her book Silent Spring,

cautioned the public against the indiscriminate use of chemical pesticides She argued that persistent sub-stances released into the environment move through-out the food chain, concentrating over time, while pests may develop a resistance to the poisons By the 1960’s, pollution from industrial and vehicular sources was beginning to be recognized as a global issue, as industrialized nations increased their spolia-tion and deplespolia-tion of natural resources In the United States, President John F Kennedy introduced a num-ber of natural resource initiatives aimed at preserving

Trang 4

wilderness areas, developing marine resources,

re-serving shorelines for public use, expanding outdoor

recreation, formulating plans for developing water

resources and developing actions against water

pollu-tion, and encouraging the development of substitutes

for resources in short supply Also, he organized the

Youth Conservation Corps to provide a workforce

to implement the program By the 1970’s, during the

administration of President Richard M Nixon, the

United States had begun to adopt environmental laws

such as the Clean Air Act and created the

Environ-mental Protection Agency as its enforcement agency

The first Earth Day to celebrate sustainable use of

nat-ural resources was in 1970

The international community came together to

discuss the environment for the first time in 1972

The United Nations held the Conference on the

Hu-man Environment in Stockholm, Sweden This

con-ference, which came to be known as the Stockholm

Convention, resulted in the creation of the United

Nations Environment Programme The 1987

publica-tion of the Brundtland Report (also known as the

Our Common Future) by the United Nations World

Commission on Environment and Development was

one of the first documents to take on the issue of

sustainable global development in modern times in

a manner similar to that espoused by Pinchot in

earlier times The goal of the Brundtland Report

was to foster global economic development that is

conservation-oriented and economically balanced

In 1980, another international organization

be-came active in conservation The International Union

for Conservation of Nature (IUCN) published World

Conservation Strategy The purpose of this publication,

and one of the ongoing goals of the IUCN, was to

assist developing nations in conservation planning to

protect and maintain natural resources: air, water,

soil, forests, and animals

Since 1992, the international community and world

leaders have continued to come together regularly to

discuss global environmental problems At the 1992

United Nations Conference on Environment and

De-velopment held in Rio de Janeiro, Brazil, much of the

discussion concerned the Brundtland Report This

conference, which came to be known as the “Rio

Earth Summit,” focused on dire predictions

concern-ing global warmconcern-ing, climate change, the ozone hole;

concerns about the depletion of natural resources,

loss of habitats, and biodiversity; and continued

con-cerns with resource pollution and depletion,

espe-cially forests and marine resources Some experts at the Rio Summit suggested that society had to choose between economic development and conserving the environment Although governments have been un-willing to make an either/or choice, one outcome of the Rio Earth Summit was the ratification by many na-tions of various international agreements to resolve some of the issues discussed at the Summit For exam-ple, the Summit led to the ratification of the 1987 Montreal Protocol, which concerns depletion of ozone

by man-made chemicals, and the 1992 Kyoto Proto-col, to limit industrial emissions that may be affecting global climate change

Sustainable development became the main topic

of discussion at the U.N 2002 Earth Summit held

in Johannesburg, South Africa Many world leaders came together to promulgate international regula-tions to address such environmental problems as im-proving air and water quality; imim-proving food access, agricultural productivity, and sanitation in develop-ing countries; and developdevelop-ing strategies and economic incentives to cope with international environmental issues related to war, poverty, and disease

Although the United States has not been a signa-tory to some of the latter-day environmental proto-cols, environmental conservation organizations, in-cluding the Sierra Club, and individuals, such as former U.S vice president Al Gore, alert the public to environmental issues Gore won the 2007 Nobel Peace Prize together with the U.N Intergovernmental Panel

on Climate Change for their efforts in getting out the conservation message on global climate change International organizations continued the conserva-tion movement in preparaconserva-tion for the 2012 Earth Summit

Population and Resource Consumption Population growth is a major factor when considering the time it will take to deplete the Earth’s nonrenew-able resources A resource is considered economically depleted after 80 percent of its known reserves have been exploited, because at that point the resource becomes too expensive for wide use As the world’s population grows, the rate of resource exploitation grows More production is necessary to satisfy the needs and wants of larger populations: More materi-als are needed, more energy is consumed, and more pollution is created

Ecologists have come to realize that the Earth is a huge ecosystem with a definite carrying capacity That

Trang 5

is, there is a limit to the number of people that can be

supported by the Earth The rate of resource

deple-tion is a funcdeple-tion both of the rate of populadeple-tion

growth and of the rate of consumption of resources

per person More resources are consumed per

indi-vidual in wealthy countries than in poor countries As

poor countries strive to develop, greater pressures are

placed on the Earth to provide resources and to

assim-ilate wastes Overpopulation occurs when there are

too many people for the available resources or when

population growth exceeds economic growth; such

conditions ultimately begin to cause damage to the

Earth’s life-support system

Water Resources: The Next Great Conflict

The availability and purity of water may be the next

great natural resource issue facing the world, and

control of water resources could lead to serious

con-flict Water not only is necessary to sustain life and

health but also is needed for food production and

various industrial uses Water resources continue to

be polluted; rivers have dried up and have been

dammed, thus reducing downriver flows to wetlands

and floodplains; underground water supplies from

aquifers have been used faster than they are

replen-ished with rainfall; and development is destroying

wetlands and other water resources and converting

them, in some cases, to deserts Because the global

so-ciety has always relied on water as a renewable

re-source, it has continued using management policies

that are no longer viable In order to maintain human

and wildlife populations, habitats, and health, and in

order to ensure that there are sufficient water

re-sources to sustain food production, water resource

management policies must change

Other Natural Resource Issues

Other global natural-resource issues concern

extrac-tions from the Earth: minerals, precious metals, and

gems such as diamonds; oil and gas drilling; and coal

mining Some of the methods used for these

extrac-tions and the consequences of accidents and spills

have raised the global consciousness about their

im-pact on the environment A search for renewable

sources to replace many of these nonrenewable

re-sources is under way within the global community

Also controversial is the negative environmental

impact of outdated rangeland management

tech-niques, uncontrolled timber harvesting, forest

de-struction, and mismanaged disposal and dumping

Many developed nations suffer from wasteful consum-erism and overuse of natural resources, such as those that provide energy Government structures to foster conservation are lacking in most developing coun-tries, and in many industrialized nations government leaders and the public are unwilling to make genuine efforts to conserve vital and dwindling natural re-sources, especially if they negatively impact economic growth Scientists predict that these abuses of the en-vironment and overuse of natural resources can no longer continue at their present rate if we want to pre-serve the future of humanity

Economics and Conservation Economics plays an important part in the balancing

of resource conservation and resource exploitation Continued growth in the use of a nonrenewable re-source can occur only for a number of years before the resource is depleted As a resource becomes scarce, the price increases, making it less affordable and reduc-ing the rate of consumption This is a self-regulatreduc-ing process that makes conservation more practical as resources become more scarce in a market-driven system

Effective conservation programs often require gov-ernmental influence, regulation, or incentives Since most resources are associated with property, govern-mental agencies that regulate land, businesses, and private citizens all make decisions that affect resource consumption The general aim of many decision mak-ers is to maximize the return on investments; conser-vation must therefore be profitable within a

reason-Mammoth Hot Springs in Yellowstone National Park (Photo

courtesy PDPhoto.org)

Trang 6

able time for people to practice it voluntarily In a free

enterprise system, resource exploitation produces

in-come from the land and provides much of the

incen-tive for land ownership Thus, resource exploitation is

likely to win out over conservation if there are no

in-centives to conserve

Conservation practices must be congruent with

economics Conservation programs are not effectively

executed when economic necessity or opportunity

in-tervenes For the most part, conservation is good for

the economy over the long term, because it improves

the efficiency of production systems However,

be-cause modern economic growth has not been

bal-anced and has not conserved natural resources, more

drastic measures may be necessary to control future

growth

One of the more controversial proposals to

com-bat economic growth issues facing the environment

are taxes on carbon-related energy sources Another

highly debated policy recommendation is over

emis-sion trading, or cap-and-trade Controlled ownership

of resources through vehicles such as trusts to avoid

depletion of natural resources—mostly

nonrenew-able resources—is another proposal being debated

Those involved in national and global political and

social debate must become serious in reaching a

con-sensus for resolving the many environmental issues

facing the world and recommend sustainable policies

that bring together economists and

environmental-ists in working for the same achievable goals

regard-ing future growth However, no matter what policies

are eventually adopted, one of the main goals of

balancing economic growth with conservation must

be continued public awareness The public and

orga-nizations are more likely to become supportive

part-ners for sustainable economic growth if they are

pro-vided with not only information on economic growth

and its effect on the environment, but also feasible,

market-driven solutions

Assessing the Future

Experts attempting to assess the future of natural

re-sources are divided in their opinions Positions range

from optimistic to direly pessimistic to somewhere

between the two extremes Those who believe that

technology can and will solve human problems have

reason to be optimistic, and, to a great extent, history

supports this view Whenever humans experience

shortages, they turn to technology for solutions—

either developing more efficient ways of finding,

ex-tracting, and using resources or finding substitutes for them

On the other hand, technology may not be able to continue solving all humankind’s problems—at least not in a timely enough manner to avoid a crisis The primary basis for the pessimistic argument is that in-creases in resource consumption rates, coupled with

an increase in population, may not allow enough time to find technological solutions to resource short-ages Furthermore, the heavy modern dependence

on nonrenewable resources is certain to cause re-source shortages

A more moderate view of the resource future sug-gests that, although there is good reason for concern, humankind has sufficient time to avoid a major crisis

if we begin moving toward a sustainable society now A sustainable society is one that allows humanity to meet its needs today without compromising its environ-ment and future needs Sustainability almost certainly requires that people in developed countries begin to live a lifestyle that includes more conservation and re-cycling, a greater dependence on renewable and per-petual resources than on nonrenewable resources, population control, and more self-discipline This view embraces the ecological approach to resource management and employs the multiple-use concept For example, forest conservation not only provides timber but also preserves a habitat for plants and animals; it can serve to help manage water resources, prevent flooding and soil erosion, and provide recre-ational areas When we reach sustainability, most of hu-mankind’s material and energy needs will be provided

by renewable and perpetual resources that should last indefinitely if properly managed

The ecological approach is holistic Based on the philosophy that all things in the natural environment are interlaced through a complex system of feedback loops, it implies that the whole is functionally greater than the sum of its parts This approach to resource management requires an understanding and anticipa-tion of the consequences of human acanticipa-tions through-out the ecosystem

Jasper L Harris, updated by Carol A Rolf

Further Reading

Castillon, David A Conservation of Natural Resources:

A Resource Management Approach 2d ed Madison,

Wis.: Brown & Benchmark, 1996

Chiras, Daniel D., and John P Reganold Natural

Re-source Conservation: Management for a Sustainable

Trang 7

Future 10th ed Upper Saddle River, N.J.: Pearson

Prentice Hall, 2009

Degregori, Thomas R The Environment, Our Natural

Resources, and Modern Technology New York: John

Wiley & Sons, 2008

Freyfogle, Eric T Why Conservation Is Failing and How It

Can Regain Ground New Haven, Conn.: Yale

Uni-versity Press, 2006

Greenland, David Guidelines for Modern Resource

Man-agement: Soil, Land, Water, Air Columbus, Ohio:

C E Merrill, 1983

Greiner, Alfred, and Will Semmler The Global

Environ-ment, Natural Resources, and Economic Growth New

York: Oxford University Press, 2008

Harper, Charles L Environment and Society: Human

Per-spectives on Environmental Issues 4th ed Upper

Sad-dle River, N.J.: Pearson/Prentice Hall, 2008

Jakab, Cheryl Natural Resources (Global Issues) North

Mankato, Minn.: Smart Apple Media, 2008

Knight, Richard L., and Courtney White, eds

Conser-vation for a New Generation: Redefining Natural

Re-sources Management Washington, D.C.: Island

Press, 2009

Krupp, Fred, and Miriam Horn Earth: The Sequel—

The Race to Reinvent Energy and Stop Global Warming.

New York: W W Norton, 2008

Loeffe, Christian V., ed Conservation and Recycling of

Resources: New Research New York: Nova Science,

2006

Miller, G Tyler, Jr Resource Conservation and

Manage-ment Belmont, Calif.: Wadsworth, 1990.

Parson, Ruben L Conserving American Resources 3d ed.

Englewood Cliffs, N.J.: Prentice-Hall, 1972

Raven, Peter H., Linda R Berg, and David M

Hassenzahl Environment 6th ed Hoboken, N.J.:

Wiley, 2008

Scott, Nicky Reduce, Reuse, Recycle: An Easy Household

Guide White River Junction, Vt.: Chelsea Green,

2007

Web Sites

Conservation International

http://www.conservation.org/Pages/default.aspx

International Union for Conservation of

Nature

http://www.iucn.org/

The Nature Conservancy

http://www.nature.org/

United Nations Environment Programme http://www.unep.org/

World Resources Institute http://www.wri.org/

World Wildlife Fund http://www.panda.org/

Worldwatch Institute http://www.worldwatch.org/

See also: Capitalism and resource exploitation; Civil-ian Conservation Corps; Conservation International; Developing countries; Endangered species; Environ-mental degradation, resource exploitation and; Envi-ronmental movement; International Union for Con-servation of Nature; Population growth; Renewable and nonrenewable resources; Sustainable develop-ment; United States; World Wide Fund for Nature

Conservation biology

Categories: Environment, conservation, and resource management; scientific disciplines

Biological scientists throughout the world are inter-ested and involved in conservation biology as a means

of preserving biodiversity Evolutionary biologists, bot-anists, ecologists, and geneticists, as well as those in applied-science management fields such as wildlife management, fisheries, and forestry, all play impor-tant roles in the broad context of conservation biology.

Background Conservation biology is a multidisciplinary field that incorporates the knowledge base and skill sets of all of the biological sciences in order to design and imple-ment methods that will attempt to ensure the long-term continuation of species, ecosystems, and ecolog-ical processes

Historical Perspective Conservation biology as a scientific discipline has its roots in the conservation movement of the early twen-tieth century Wildlife scientists such as Aldo Leopold, foresters such as Gifford Pinchot, and progressive pol-iticians such as Theodore Roosevelt wielded tremen-dous influence in both conservation and preservation efforts In the 1960’s and 1970’s, there was

Trang 8

phenome-nal growth of community ecology data and important

ecological theories, such as island biogeography,

pro-moted by Robert H MacArthur, Edward O Wilson,

and Daniel Simberloff Social trends of this time

pe-riod also contributed to the development of this field,

as many people embraced the environmental

move-ment, and, accordingly, a number of significant pieces

of environmental legislation were passed As more

and more species either neared extinction or became

extinct, the movement to “save the planet” became

ever more insistent

Consequently, much of the focus of conservation

biology since the 1970’s has been on saving

endan-gered and threatened species The United States Fish

and Wildlife Service (USFWS) defines an endangered

species as one that is in danger of extinction

through-out all or a significant portion of its range A

threat-ened species is likely to become endangered in the

foreseeable future The USFWS tracks the numbers

of endangered and threatened species both within

the United States and around the world In 2009, the

number of endangered animal species within the

United States was 410, with 163 listed as threatened

Bird, fish, mammal, and clam species topped the

en-dangered animal list The enen-dangered plant species

total was 600; 146 plant species were threatened

Throughout the remainder of the world, 527 animal

species were endangered and 44 were threatened; 1

plant species was listed as endangered and 2 were

threatened Obviously, these numbers vary from year

to year; nevertheless, the data support the need for

worldwide conservation efforts

Minimum Viable Populations

In the past in Europe and North America, most

ex-tinctions or local extirpations of species occurred

because of overhunting Examples of this in North

America include bison, cougar (in the eastern U.S.,

with the exception of the remnant Florida panther

population), red wolf, and passenger pigeon In

Eu-rope, the wolf, wild boar, goshawk, and capercaillie

were gone by the nineteenth century

Although overhunting is still a reason for species

decline in some parts of the world, today the primary

cause for the large number of endangered and

threat-ened species is habitat fragmentation This occurs

when a large area of habitat is divided into a number

of smaller patches comprising a smaller total area

Of-ten these smaller patches are unsuitable for species of

the original habitat, and thus dispersal of species into

the “new” habitat can be low Conservation biologists face the challenge of preserving as many individuals

of the endangered or threatened species as possible within suitable habitat, thereby enabling genetic di-versity within the species to continue As a result of fragmentation, conservation biologists are often try-ing to discover a minimum viable population (MVP) number for each imperiled species Although the number of five hundred individuals has often been used as a base guideline for MVP, many scientists ar-gue that the specific number of individuals needed to ensure genetic diversity varies by species and that no set number applies to all species

If the MVP becomes too low, serious genetic prob-lems within the population may occur, as the number

of individuals is simply too low to prevent inbreeding Probably the best known example of this is the chee-tah, a species in which almost all of the individuals are now related to one another Biologists have noted del-eterious genetic effects such as sperm malformation and high infant mortality within the cheetah tion With species that have greatly reduced popula-tion numbers, conservapopula-tion biologists are faced with the management challenge of reducing inbreeding, encouraging outbreeding if enough individuals re-main, and seeking to enable members of the species

to migrate, if possible

Reserves Along with determining MVPs for endangered and threatened species, biologists seek to meet the man-agement goals mentioned above by creating or main-taining suitable reserve sites As with deciding on MVP, determining the necessary size and shape of a reserve can be extremely difficult and is again species dependent Based on their research, several conserva-tion biologists have suggested that a circular shape for reserves is best in order to minimize dispersal dis-tances and to minimize the amount of edge habitat Within both temperate and tropical forest areas, neg-ative edge effects include temperature and humidity changes, wind exposure, tree mortality, and penetra-tion of light into formerly shaded areas

Many researchers recommend single large reserve areas for large herbivores, large carnivores, and birds, rather than a number of small reserves, unless an ex-tensive corridor of suitable habitat can connect the small reserves The efforts of national conservation organizations are often necessary to establish and maintain large nature reserves, whereas regional and

Trang 9

even local groups may be able to keep smaller reserves

going for species that do not require large expanses of

habitat in which to survive

Active management of reserves is usually necessary

in order to provide continued suitable habitat for

en-dangered and threatened species Often exotic

vege-tation must be removed from reserves, or a certain

successional stage of vegetation must be maintained

Elimination of exotic animal species, such as wild

boars or brown-headed cowbirds, may be needed

Once land has been set aside for the preservation of

imperiled species, conservation biologists must be

vigilant in its management in order to preserve the

biodiversity of the area

Lenela Glass-Godwin

Định dạng
Số trang	10
Dung lượng	178,96 KB