Transcript Human Impact on Resources and Ecosystems

Biodiversity Issues
Chapter 12
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Biodiversity Loss and Extinction
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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.
 Natural and common event in the history
of biological evolution.
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Causes of Extinction
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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.
Species Likely to Go Extinct
– Small, dispersed populations.
 Successful breeding is difficult.
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Table 12.1
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Species Likely to Go Extinct
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Organisms in small, restricted areas.
– Environmental changes have large effect.
Specialized Organisms
– Relying on constancy of few key factors.
Organisms at higher trophic Levels.
– Low population sizes and reproductive
rates.
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Extinction as a Result of Human Activity
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As human population grew, and tools
became more advanced, the impact a single
human could have on surroundings
increased.
– Environmental modifications allowed
larger, dense human populations to arise.
 At expense of previously existing
ecosystems.
 Nearly all earth’s surface has been
affected in some way by human
activity.
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Describing Biodiversity
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Genetic Diversity is a term used to describe
the number 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.
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Genetic Diversity
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Influences on 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.
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Influences on a Population’s Genetic Diversity
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Population Size
– The smaller the population, the less
genetic diversity it can contain.
 Fewer variations for each characteristic.
Selective Breeding
– Elimination of undesirable characteristics.
 Domesticated Plants and Animals.
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Species Diversity
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Species diversity is a measure of the number
of different species present in an area.
– Species Richness - Number of different
kinds of species.
– Taxonomic Richness - Takes into account
the number of different taxonomic
categories of the species present.
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Species Diversity
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When humans exploit an area, they influence
species diversity.
– Convert natural ecosystems to humanmanaged ecosystems.
 Harvest certain species for their use.
 Specifically eliminate species that
compete with desirable species.
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Species Diversity
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Estimates of 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.
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Ecosystem Diversity
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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 ecosystems.
 Deserts
 Each is different and has specific
organisms typical to the region.
 Local topographic conditions create
unique patches of landscape.
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The Value of Biodiversity
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Value of Biological and Ecosystem Services
– Humans rely on organic molecules
produced by other organisms for food.
– Vegetation holds soil together and protects
watersheds.
– Plants remove carbon dioxide from the
atmosphere.
– Decomposers recycle organic wastes.
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The Value of Biodiversity
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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.
 Some resources are difficult to assign
specific monetary value:
 Wildlife
 Medicinal Plants
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Ethical Values
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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.
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Ethical Values
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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.
 Important in determining how society will
approach threats to biodiversity.
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Threats to Biodiversity
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Four major human activities threaten to
reduce biodiversity.
– Habitat Loss
– Overexploitation
– Introduction of Exotic Species
– Persecution of Pest Organisms
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Causes of Extinction
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Habitat Loss
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World Conservation Union estimates that
80%-90% of threatened species are a result of
habitat loss or fragmentation.
– Habitat loss and fragmentation are thought
to be a major cause of past extinctions.
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Conversion to Agriculture
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About 40% of world’s land surface converted
to cropland and permanent pasture.
– Most productive natural ecosystems are
the first to be modified by humans.
 Pressures to modify the environment are
greatest in areas with high population
density.
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Forestry Practices
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Originally, 1/2 of US, 3/4 of Canada, and
almost all of Europe was originally forested.
– Because of increasing human population
growth, forested areas are under
increasing pressure to provide wood
products and agricultural land.
 Deforestation
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Changes in Forest Area
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Managing Forest Ecosystems
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Modern forest management involves a
compromise that allows economic
exploitation while maintaining some
environmental values of the forest.
– Forested areas effectively reduce erosion.
 Loss of soil (nutrients) reduces soil
fertility.
 Road building in forests increases
erosion.
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Environmental Implications of
Various Harvesting Methods
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Clear Cutting - Removal of all trees in an
area. Economical but increases erosion,
especially on steep slopes.
Patch-Work Clear Cutting - Clear cutting in
small, unconnected patches; preserves
biodiversity.
Selective Harvesting - Single tree-harvesting.
Not as economical, but reduces ecosystem
damage.
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Special Concerns About Tropical Deforestation
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Tropical forests have greater species diversity
than any other ecosystem.
– Not easy to regenerate after logging due to
poor soil characteristics.
 Currently, few tropical forests are being
managed for long-term productivity.
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Special Concerns About Tropical Deforestation
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Significantly reduces species diversity.
Impacts climate via lowered transpiration.
Deforested lands are easily eroded.
CO2 trap - Increased global warming.
Human population pressure is greatest in
tropics, and still increasing.
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Plantation Forestry
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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.
– Mature rate as low as 20 years (vs. 100).
 Quality of lumber reduced.
 Low species diversity and wildlife value.
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Rangeland and Grazing Practices
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Rangelands - Lands too dry to support crops,
but receive enough precipitation to support
grasses and drought-resistant shrubs.
– Often used to raise low-density populations
of domesticated, or semi-domesticated
species.
 Wildlife are usually introduced species.
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Use of Rangelands
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Rangeland and Grazing Practices
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Conversion of rangelands by domesticated
animals has major impacts on biodiversity.
– Selective eating habits of livestock tend to
reduce certain species of native plants and
encourages others.
 Important to regulate number of livestock
on rangelands, especially in dry areas.
 Desertification
 Over-grazing
 Firewood cutting
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Desertification
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Habitat Loss in Aquatic Ecosystems
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In marine ecosystems, much of the harvest is
restricted to shallow parts of the ocean
where bottom-dwelling fish can be easily
harvested.
– Trawls and nets dragged along the bottom.
 Habitat Damage
– About 25% of catch is undesirable, and
thus discarded.
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Habitat Loss in Aquatic Ecosystems
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Freshwater systems are often modified for
navigation, irrigation, flood control, or power
production.
– May alter natural ecosystem and change
numbers or kinds of aquatic organisms
present.
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Changes in World Marine Fish Harvests
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Conversion to Urban and Industrial Uses
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About 4.3% of U.S. land is developed as
urban centers, industrial sites, and
transportation infrastructure.
– Large proportion covered with
impermeable surfaces that prevent plant
growth and divert rainfall.
 Difficult to generalize impact of urban
centers on a worldwide basis.
 Trend is toward greater urbanization.
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Overexploitation
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According to World Conservation Union,
overexploitation is responsible for over 30%
of endangered animal species and 8% of
endangered plant species.
– World Wildlife Fund estimates illegal trade
in wild animals globally produces $2 - $35
billion annually.
 Already resulted in local extinctions.
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Overfishing of Marine Fisheries
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U.N. estimates 70% of world’s marine
fisheries are over-exploited or are in danger
of being fully exploited.
– Amount of fish caught has remained
relatively constant since 1989.
 Commercial fishing industry has been
attempting to market species previously
regarded as unacceptable.
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Aquaculture
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Fish farming is becoming increasingly
important as a source of fish production.
– Currently, about 60% of all aquaculture
production is from freshwater systems.
 Problems
 Nutrient overloads
 Escape into natural waters
 Land conversion
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Unsustainable Harvest of Wildlife and Plants
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Meat from wild animals is often referred to as
bush meat.
– Hunting of wildlife is a part of all
subsistence cultures.
 Wildlife Conservation Society estimates
70% of wildlife species in Asia and Africa
and about 40% of species in Latin
America are being hunted unsustainably.
 Endangered species such as
chimpanzees and gorillas are often
harvested.
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Unsustainable Harvest of Wildlife and Plants
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Harvest of living animals for the pet and
aquarium trade is a significant problem.
– 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
 Traditional Medicines
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Introduction of Exotic Species
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Some exotic introductions are purposeful,
while others are accidental.
– 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.
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Introduction of Exotic Species
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Introduction of disease has had considerable
impact on American forests.
– Chestnut Blight
– Dutch Elm Disease
Various insects have had effect on
ecosystem structure.
– Asian Longhorned Beetle
Freshwater ecosystems greatly affected.
– Zebra Mussel
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Control of Pest Organisms
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Systematic killing of certain organisms that
interfere with human activities also results in
reduced biodiversity.
– Large Predators
 Preyed on domestic animals.
– Passenger Pigeons
 Increased conversion of forested land.
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Control of Pest Organisms
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Predator and competitor control activities are
still used in some special situations.
– Generally not considered to be costeffective in most cases.
 Wolves in Northern areas are exception.
 Control of cowbird populations have
been used to enhance breeding success
of Kirtland’s Warblers.
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What is Being Done to Preserve Biodiversity?
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World Conservation Union (IUCN) estimates
by the year 2000, at least 500,000 species of
plants and animals have been exterminated.
– IUCN classifies species in danger of
extinction into four categories:
 Endangered
 Vulnerable
 Rare
 Indeterminate
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Legal Protection
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Most interest in extinction prevention occurs
in developed countries. Most vulnerable
species already eliminated.
– Less-developed and developing countries
have both highest population growth and
the majority of the world’s species.
 More concerned with immediate needs
of food and shelter than long-range
issues such as species extinction.
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Legal Protection
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U.S. Endangered Species Act (ESA -1973)
– Gave U.S. government jurisdiction over
threatened and endangered 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.
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Legal Protection
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Endangered Species - Very low populations,
could become extinct in very near future.
Threatened Species - Could become extinct
if a critical environmental factor is changed.
– 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.
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Legal Protection
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Many areas in the world have had minimal
human impact.
– Some are remote and may have harsh
environmental conditions.
 Wilderness Act (1964) - Wilderness:
 “An area where the earth and its
community of life are un-trampled by
man, where man himself is a visitor
who does not remain.”
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Sustainable Management of Wildlife Populations
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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.
 Fire to eliminate poor habitats.
 Kirtland Warblers - Jack Pine
stands.
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Population Assessment and Management
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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 most wild animals
can maintain a sizeable population.
 High reproductive capacities and
heavy protection can cause very large
populations.
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Population Assessment and Management
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Wildlife management often involves
harvesting for sport and meat.
– Hunting regulation is crucial.
 Seasons usually occur in the fall to take
advantage of surplus animals.
When populations get too small, artificial
introductions can be implemented.
– Native species for augmentation.
– Non-native species for empty niches.
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Managing a Wildlife Population
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Special Issues with Migratory Animals
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Migratory birds can travel thousands of
kilometers.
– North in Spring to reproduce.
– South in Fall to escape cold temperatures.
International agreements necessary to
maintain appropriate habitat.
– Canada
– United States
– Mexico
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Migration Routes for North American Waterfowl
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Sustainable Management of Fish Populations
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Coastal regions are most productive regions
of the oceans.
– Sunlight penetration - shallow - warm.
– Nutrient deposition from land.
– Wind/wave action stirs nutrients.
 Fishing pressure is concentrated.
 One of the major problems associated
with the management of marine
fisheries is achieving agreement on
harvest limits.
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Sustainable Management of Fish Populations
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Humans have easy access to freshwater
ecosystems.
– Typically easier to regulate because of
containment within a smaller political region.
– Many N.A. freshwater fisheries are primarily
managed for sport fishery.
 Fisheries managers must balance:
 Sport fisheries
 Commercial harvesters
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Fig. 12.2
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Fig. 12.3
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Fig. 12.5
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Fig. 12.7
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Fig. 12.8
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Fig. 12.9
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Fig. 12.10
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Fig. 12.11
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Fig. 12.12
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Fig. 12.14
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Fig. 12.15a
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Fig. 12.15b
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Fig. 12.16
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Fig. 12.17
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Fig. 12.18
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Fig. p.251
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Fig. p.277
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Table 12.2
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Table 12.3
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Table 12.4
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Table 12.5
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