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Environmental Science
A Study of Interrelationships
Eleventh Edition
Enger & Smith
Chapter 11
Biodiversity Issues
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Biodiversity Issues
Outline
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Biodiversity Loss and Extinction
Describing Biodiversity
The Value of Biodiversity
Threats to Biodiversity
What Is Being Done to Preserve Biodiversity?
Biodiversity Loss and Extinction
 Biodiversity is a broad term used to describe
the diversity of genes, species, and ecosystems
in a region.
 Extinction is the elimination of all the individuals
of a particular species.
• Extinction is a natural and common event in the
history of biological evolution.
• It, and the resulting loss of biodiversity, is also a major
consequence of human domination of the Earth.
Biodiversity Loss and Extinction
 Local extinctions, although relatively common,
indicate the future of a species is not
encouraging.
 As population is reduced in size, some of the
genetic diversity is likely to be lost.
 Certain kinds of species are more likely to go
extinct than others:
• Species with small, dispersed populations
– Successful breeding is difficult.
Biodiversity Loss and Extinction
• Organisms in small, restricted areas, such as islands.
– Environmental changes have large effect.
• Specialized organisms
– Relying on constancy of a few key factors.
• Organisms at higher trophic levels.
– Low population sizes and reproductive rates.
Biodiversity Loss and Extinction
Biodiversity Loss and Extinction
 As human populations grew, and their tools
became more advanced, the impact a single
human could have on surroundings increased.
 Environmental modifications allowed larger, dense
human populations to survive, but at the expense of
previously existing ecosystems.
 Nearly all Earth’s surface has been affected in
some way by human activity.
Describing Biodiversity
 Genetic diversity is a term used to describe the
number of kinds of genes present in a
population.
• High genetic diversity indicates many different kinds
of genes present in individuals of a population.
• Low genetic diversity indicates nearly all individuals
share the same genes and therefore the same
characteristics.
Describing Biodiversity
 Several things influence a population’s genetic
diversity:
• Mutations introduce new genetic information into a
population by modifying current genes.
• Migration allows movement of genes from one population
to another.
• Sexual reproduction generates new genetic
combinations.
Describing Biodiversity
• Population size is an important factor: The smaller the
population, the less genetic diversity it can contain.
– There are fewer variations for each characteristic.
– Random events can significantly alter the genetic diversity
in small populations.
• Selective breeding can affect diversity because
undesirable characteristics are eliminated.
– Many domesticated plants and animals could not survive
without human help.
Describing Biodiversity
 Species diversity is a measure of the number
of different species present in an area.
• Species richness refers to the number of different
kinds of species in an area.
• Taxonomic richness takes into account the number
of different taxonomic categories of the species
present.
Describing Biodiversity
 When humans exploit an area, they influence
species diversity.
• They convert natural ecosystems to human-managed
ecosystems.
– They harvest certain species for their use.
– They specifically eliminate species that compete with
desirable species.
– They introduce nonnative species to an area.
Describing Biodiversity
 Estimates of the actual
number of species range
from a few million to 100
million.
• About 1.4 million species have
been described.
– Many species are naturally
rare, and others live in areas
difficult to reach.
Describing Biodiversity
 Ecosystem diversity is a measure of the number
of kinds of ecosystems present in an area.
 Many regions of the world appear to be quite
uniform in terms of the kinds of ecosystems
present.
• For example, many parts of the world are deserts:
– While there are general similarities, each is different and
has specific organisms typical to the region.
– Local topographic conditions create unique patches of
landscape.
The Value of Biodiversity
 Biological and Ecosystem Services Values
• Humans rely on organic molecules produced by other
organisms for food.
• Each organism is involved in a vast network of
relationships with other organisms.
• Accidental extinction of one of these species could be
devastating to the ecosystem and the humans who
use it.
– Vegetation holds soil together and protects watersheds.
– Plants remove carbon dioxide from the atmosphere.
– Decomposers recycle organic wastes.
The Value of Biodiversity
 Choices between competing uses for ecosystems
are often determined by economic values.
• Value can be assigned to services provided by intact,
functioning ecosystems.
– Current estimate of $33 trillion per year, but that figure may
be low.
• Some resources are difficult to assign specific monetary
value:
– Wildlife (consumed by those who harvest it)
– Medicinal plants
The Value of Biodiversity
 A case can be made that all species have an
intrinsic value and a fundamental right to exist.
• Extinction is not necessarily bad, but human-initiated
extinction is.
• Experiencing natural landscapes and processes is an
important human right.
The Value of Biodiversity
 The values held by a person are typically
shaped by experience.
• As the shift from rural to urban continues, there is
continual erosion of natural experiences that can
shape the values of people.
• These values are important in determining how
society will approach threats to biodiversity.
Threats to Biodiversity
 Four major human activities threaten to reduce
biodiversity.
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Habitat loss
Overexploitation
Introduction of exotic species
Persecution of pest organisms
Threats to Biodiversity
Causes of extinction
Threats to Biodiversity
 The World Conservation Union estimates that 80%90% of threatened species are under threat as a
result of habitat loss or fragmentation.
 Habitat loss and fragmentation are thought to be a
major cause of past extinctions.
Threats to Biodiversity
 About 40% of the world’s land surface has been
converted to cropland and permanent pasture.
 Typically, the most productive natural
ecosystems (forests and grasslands) are the first
to be modified by humans.
 Pressures to modify the environment are
greatest in areas with high population density.
Threats to Biodiversity
 Originally, half of the U.S., three-fourths of
Canada, and almost all of Europe, and
significant portions of the rest of the world were
forested.
 Deforestation is the process of destroying a
forest, often for the purposes of fuel, building
materials, or to clear land for farming.
Threats to Biodiversity
 Modern forest management practices involve a
compromise that allows economic exploitation while
maintaining some environmental values of the
forest.
• Forested areas effectively:
– Reduce erosion.
– Reduce runoff.
– Modify the climate.
– Provide recreational opportunities.
Threats to Biodiversity
Changes in forest area
Threats to Biodiversity
 Clear cutting is the removal of all trees in an area.
It is economical but increases erosion, especially
on steep slopes.
 Patchwork clear cutting is clear cutting in small,
unconnected patches; preserves biodiversity.
 Selective harvesting is single species tree
harvesting. It is not as economical, but reduces
ecosystem damage.
Threats to Biodiversity
Clear cutting
Threats to Biodiversity
 Tropical forests have greater species diversity than
any other ecosystem.
 They are not as likely as temperate forests to
regenerate after logging due to poor soil
characteristics.
 Currently, few tropical forests are being managed
for long-term productivity.
Threats to Biodiversity
 Several concerns are raised by tropical
deforestation:
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It significantly reduces species diversity in the world.
It impacts the climate via lowered transpiration.
Deforested lands are easily eroded.
Without the forests to trap CO2, there may be increased
global warming.
• Human population pressure is greatest in tropics, and
still increasing.
Threats to Biodiversity
 Many lumber companies maintain forest plantations
as crops and manage them in the same way farmers
manage crops.
• Plant single species, even-aged forests of fast growing
hybrid trees.
• Competing species are controlled by fire, and insects
controlled by spraying.
• Trees mature to harvestable size in as low as 20 years (vs.
100).
– Quality of lumber reduced.
– Low species diversity and wildlife value.
Threats to Biodiversity
 Rangelands are lands too dry to support crops,
but receive enough precipitation to support
grasses and drought-resistant shrubs.
 They are often used to raise low-density
populations of domesticated or semidomesticated animals.
 Wildlife are usually introduced species not native
to the region.
Threats to Biodiversity
Use of rangelands
Threats to Biodiversity
 The conversion of rangelands to grazing by
domesticated animals has major impacts on
biodiversity.
• Selective eating habits of livestock tend to reduce certain
species of native plants and encourage others.
• Important to regulate number of livestock on rangelands,
especially in dry areas.
– Overgrazing is a severe problem where human population
pressures are great.
– Desertification is the process of converting arid or semiarid
land to desert because of improper human use.
Threats to Biodiversity
Desertification
Threats to Biodiversity
 In marine ecosystems, much of the harvest is
restricted to shallow parts of the ocean where
bottom-dwelling fish can be easily harvested.
 Trawls are nets dragged along the bottom.
• They disturb the seafloor and cause habitat damage.
 About 25% of catch is undesirable, and thus
discarded, but they are usually dead, and their
removal further alters the ecological nature of
the seafloor.
Habitat Loss in Aquatic Ecosystems
 Freshwater systems are often modified for
navigation, irrigation, flood control, or power
production.
 All of these processes may alter natural
ecosystems and change numbers or kinds of
aquatic organisms present.
Threats to Biodiversity
Changes in world marine fish harvests 1950-1995
Threats to Biodiversity
 About 4.3% of U.S. land is developed as urban
centers, industrial sites, and transportation
infrastructure.
• Many areas are covered with impermeable surfaces that
prevent plant growth and divert rainfall.
• It is difficult to generalize about the impact of urban
centers on a worldwide basis.
• The trend is toward greater urbanization.
Threats to Biodiversity
 According to the World Conservation Union,
overexploitation is responsible for over 30% of
endangered animal species and 8% of
endangered plant species.
 The World Wildlife Fund estimates illegal trade
in wild animals globally produces $2–$30.5
billion annually.
• These activities have already resulted in local
extinctions.
Threats to Biodiversity
 U.N. estimates 70% of world’s marine fisheries
are overexploited or are fully exploited and in
danger of being overexploited.
• Amount of fish caught has remained relatively
constant since 1989.
• The commercial fishing industry has been attempting
to market species previously regarded as
unacceptable.
Threats to Biodiversity
 Fish farming (aquaculture) is becoming
increasingly important as a source of fish
production.
 Currently, about 60% of all aquaculture
production is from freshwater systems.
 The environmental impacts are similar to those
of marine systems:
• Nutrient overloads
• Escape into natural waters
• Land conversion
Threats to Biodiversity
 Meat from wild animals is often referred to as bush
meat.
 The Wildlife Conservation Society estimates 70% of
wildlife species in Asia and Africa and about 40% of
species in Latin America are being hunted
unsustainably.
• Hunting of wildlife is a part of all subsistence cultures.
• Many kinds of wildlife are considered delicacies and are
highly prized for the home and restaurant trade.
Threats to Biodiversity
 Harvest of living animals for the pet and aquarium
trade is a significant problem.
• The method of capture is often problematic.
– Destruction of bird nests.
– Toxins used to stun fish.
 Wildlife are also hunted because parts of the
animal may have particular value.
– Ivory and animal skins
– Traditional medicines
Threats to Biodiversity
 Some introductions of exotic species are
purposeful, while others are accidental.
 The World Conservation Union estimates about
30% of birds and 15% of plants are threatened
because they are unable to successfully compete
against invasive exotic species.
Threats to Biodiversity
 Introduction of disease has had considerable
impact on American forests.
• Chestnut blight
• Dutch elm disease
 Various insects have had an effect on ecosystem
structure.
• Asian longhorned beetle
 Freshwater ecosystems have been greatly affected.
• Zebra mussel
Threats to Biodiversity
The Asian longhorned beetle
Threats to Biodiversity
 Systematic killing of certain organisms that
interfere with human activities also results in
reduced biodiversity.
• Large predators have been locally exterminated
because they preyed on domestic animals.
• Passenger pigeons became extinct primarily because
of increased conversion of forested land.
Threats to Biodiversity
 Predator and competitor control activities are still
used in some special situations.
• It is generally not considered to be cost-effective in
most cases.
– Hunting and trapping of wolves in Alaska and Canada is
an exception.
– Control of cowbird populations has been used to
enhance breeding success of Kirtland’s warblers.
What Is Being Done to Preserve
Biodiversity?
 The World Conservation Union (IUCN) estimates
by the year 2010, at least 500,000 species of plants
and animals may have been exterminated.
• IUCN classifies species in danger of extinction into four
categories:
– Endangered
– Vulnerable
– Rare
– Indeterminate
What Is Being Done to Preserve
Biodiversity?
 Awareness and concern about loss of
biodiversity are high in many developed
countries.
 Most vulnerable species in these areas have
already been eliminated.
 Loss of biodiversity is not a high priority for the
general public in developing countries.
 They are more concerned with immediate needs
of food and shelter than long-range issues such
as species extinction.
What Is Being Done to Preserve
Biodiversity?
 In the U.S., the primary action related to the
preservation of biodiversity involved the passage
of the Endangered Species Act (1973).
 This legislation designates species as
endangered or threatened and gives the U.S.
government jurisdiction over those species.
• Directs that no activity by a government agency
should lead to the extinction of an endangered
species.
• Directs government agencies to use whatever means
necessary to preserve the species in question.
What Is Being Done to Preserve
Biodiversity?
 Endangered species are those that have such
small numbers that they are in immediate
danger of becoming extinct.
 Threatened species could become extinct if a
critical environmental factor is changed.
• The preservation question ultimately becomes one of
assigning value to the species.
• Amendments to ESA have weakened ability of U.S.
government to add new species to the list.
What Is Being Done to Preserve
Biodiversity?
 The designation of certain areas as wilderness is a
sensitive issue.
 The Wilderness Act (1964) defines wilderness as
“an area where the Earth and its community of life
are untrammeled by man, where man himself is a
visitor who does not remain.”
What Is Being Done to Preserve
Biodiversity?
 Habitat Analysis and Management
• Animals have highly specific habitat requirements that
change throughout the year.
• Steps can be taken to alter habitat and improve species
success.
• Modifications made to enhance the success of a species
are known as habitat management.
What Is Being Done to Preserve
Biodiversity?
 Game species are often managed so they do not
exceed carrying capacity of their habitat.
 Wildlife managers use population censuses to
check if populations are within appropriate levels.
 With suitable habitat and protection, most wild
animals can maintain a sizeable population.
 High reproductive capacities and heavy protection
have caused very large populations to arise from
once-rare animals.
What Is Being Done to Preserve
Biodiversity?
 Wildlife management often involves harvesting
for sport and meat.
• Regulating hunting activity is an important population
management technique.
• Seasons usually occur in the fall so surplus animals
are taken before the challenges of winter.
 When populations get too small, artificial
introductions can be implemented.
• Native species can be reintroduced to areas where
they had been extinct.
• Non-native species are introduced for empty niches.
What Is Being Done to Preserve
Biodiversity?
Managing a wildlife population
What Is Being Done to Preserve
Biodiversity?
 Migratory birds can travel thousands of
kilometers.
• They travel north in spring to reproduce.
• They travel south in fall to escape cold temperatures.
 International agreements may be necessary to
maintain appropriate habitat.
What Is Being Done to Preserve
Biodiversity?
Migration routes for North American waterfowl
What Is Being Done to Preserve
Biodiversity?
 Coastal regions are most productive regions of
the oceans.
• Sunlight penetration of shallow water makes it warm.
• Nutrient deposition from land makes this region fertile.
• Wind/wave action stirs nutrients.
 Fishing pressure is concentrated here.
 One of the major problems associated with the
management of marine fisheries is achieving
agreement on harvest limits.
What Is Being Done to Preserve
Biodiversity?
 Humans have easy access to freshwater
ecosystems, so management of these systems is
much more intense.
 They are typically easier to regulate because of
containment within a smaller political region.
 Many N. American freshwater fisheries are primarily
managed for sport fishery.
 Fisheries biologists pay special attention to water
quality.
Summary
 Loss of biodiversity has become a major concern.
 Ecosystems involve the interactions of organisms
and their physical environment.
 The loss of key species can result in the loss of a
type of ecosystem either locally or worldwide.
 Functioning ecosystems and their component
organisms provide many valuable services that are
often overlooked because they are not easily
measured in economic terms.
Summary
 Many people also consider the loss of
biodiversity to be an ethical problem.
 The primary causes of habitat loss are by:
• Humans converting ecosystems to agriculture and
grazing
• Overexploitation by harvesting species at
unsustainable levels
• Introduction of exotic species that disrupt ecosystems
and compete or prey on native organisms
• Purposeful killing of pest organisms such as large
predators.
Summary
 Protection of biodiversity typically involves legal
protections by national laws and international
agreements, and management of the use of
species and ecosystems at sustainable levels.