Biodiversity Issues

1
Biodiversity Issues

• Chapter 12

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Biodiversity Loss and Extinction

• Biodiversity is a broad term used to describe the
  number 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.
• 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 earths 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 Populations 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 Populations 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

• 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.
• Most undescribed species are insects or not
  useful to man.

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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 uniform
• 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
• 1. Selfish - practical
• Humans rely on organic molecules produced by
  other organisms for food.
• 2. Ecosystem
• Vegetation holds soil together and protects
  watersheds. (Ecosystem)
• 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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3. 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 worlds 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 - Deforestation

• Originally, 1/2 of US, 3/4 of Canada, and almost
  all of Europe was originally forested. Now
  Rainforest being destroyed.
• Increasing human population growth, forested
  areas increasing pressure to provide wood
  products and agricultural land.

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Changes in Forest Area
21
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

• 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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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.
• Freshwater systems are often modified for
  navigation, irrigation, flood control, or power
  production.

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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 worlds 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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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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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
• Endangered
• Vulnerable
• Rare
• Indeterminate

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US Endangered Species Act - 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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The Wilderness Act - 1964

• Many areas in the world have had minimal human
  impact.
• Some are remote and may have harsh environmental
  conditions.
• - 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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Migratory Bird Act 1918 (new 1998)

• 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 Fishery Act 1996

• Calls for sustainable management of worlds
  fisheries.
• Coastal regions are most productive regions of
  the oceans.
• 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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Marine Mammal Act - 1972

• Some marine mammal species or stocks may be in
  danger of extinction or depletion as a result of
  human activities
• These species or stocks must not be permitted to
  fall below their optimum sustainable population
  level (depleted)
• Measures should be taken to replenish these
  species
• There is inadequate knowledge of the ecology and
  population dynamics and
• Marine mammals have proven to be resources of
  great international significance.