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Biodiversity Issues

Chapter 12

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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.Natural and common event in the history

of biological evolution.

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Causes of 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.• 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

• 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

• 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

• 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

• Influences on a Population’s Genetic Diversity– Mutations

Introduce new genetic information into a population by modifying current genes.

– MigrationAllows 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

• 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

• 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

• When humans exploit an area, they influence species diversity.– Convert natural ecosystems to human-

managed ecosystems.Harvest certain species for their use.

Specifically eliminate species that compete with desirable species.

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Species Diversity

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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.

IvoryTraditional Medicines

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Introduction of Exotic Species

• 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

• 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

• 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

• Predator and competitor control activities are still used in some special situations.– Generally not considered to be cost-

effective 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?

• 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:EndangeredVulnerableRareIndeterminate

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Legal Protection

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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