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57
Introduction
• The problem of human-caused extinction of
species led to the development of the discipline of
conservation biology: the scientific study of how
to preserve the diversity of life.
• Conservation biology draws on population
genetics, evolution, biogeography, wildlife
management, economics, and sociology.
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Why Care about Species Extinctions?
• The value of biodiversity to humans:
 Humans depend on other species for food, fiber,
and medicine.
 Humans derive aesthetic pleasure from
interacting with other organisms.
 Causing the extinction of other species raises
serious ethical issues.
 Extinctions make the study of ecological
relationships and species interactions difficult.
 Species are necessary for the function of the
ecosystems of which they are a part.
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Why Care about Species Extinctions?
• The benefits provided to humans by functioning
ecosystems are enormous.
• These include, among others, prevention of soil
erosion, regulation of hydrologic cycles, and
detoxification and recycling of waste products.
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Estimating Current Rates of Extinction
• The number of species on an island increases
with the size of the island.
• Conservation biologists have applied this
species–area relationship to habitat patches on
the mainland as well.
• Findings suggest that a 90% loss of habitat will
result in the loss of half of the species living there.
• If the current rate continues, about 1 million
species living in the tropical evergreen forests will
become extinct in this century.
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Estimating Current Rates of Extinction
• To assess extinction risk for a population,
biologists analyze many factors including genetic
variation, morphology, physiology, behavior, and
environment.
• Species in imminent danger over a significant
portion of their range are labeled endangered
species.
• Species that are likely to become endangered in
the near future are labeled threatened species.
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Estimating Current Rates of Extinction
• Rarity is not always a reason for concern.
• However, species in which a few individuals are
confined to a small range are more likely to be
eliminated by local disturbances such as fire and
disease.
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Preserving Biodiversity
• The human activities that threaten species include
habitat destruction, introduction of invasive
species, overexploitation, disease, alteration of
disturbance patterns (urban sprawl), and climate
change.
• Conservation biologists determine how these
activities are affecting species and devise
strategies to preserve endangered or threatened
species.
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Preserving Biodiversity
• Habitat loss is the most important cause of
endangerment of species in the U.S., especially
species that live in fresh waters.
• As habitats are destroyed, the remaining patches
become fragmented (smaller and more isolated).
• Small patches cannot maintain populations that
require larger areas and can support only small
numbers of species that can survive in them.
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Preserving Biodiversity
• People have moved organisms between
continents deliberately and accidentally.
• A species that has evolved in a community and
become accustomed to the natural predators or
competitors may be driven to extinction by newly
introduced predators or competitors.
• A major human-caused environmental change is
the introduction of non-native species that then
become invasive in the their new environments.
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Preserving Biodiversity
• Hundreds of species of plants have been
introduced as ornamentals. An example is purple
loosestrife.
• Almost half of the medium-sized marsupials in
Australia have become extinct due to the
introduction of predators (cats and foxes) and
competitors (rabbits) to the continent.
• Proliferation of introduced pathogens, such as the
fungus that causes Dutch elm disease, has
caused much destruction to North American
forests.
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Preserving Biodiversity
• The best way to reduce the damage caused by
invasive species is to prevent their establishment
in the first place.
• The shipping industry spreads invasive species in
ballast water, which is pumped into ships at one
port and discharged at another. Deoxygenating
ballast water before it is pumped out would control
the problem of invasive aquatic species.
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Preserving Biodiversity
• Until recently, humans caused most extinctions
primarily by overhunting.
• The passenger pigeon, one of the most abundant
species of bird in North America in the 1800s,
became extinct by 1914 due to hunting.
• Elephants and rhinoceroses are threatened with
extinction because poachers kill them for their
tusks and horns.
• The houseplant and pet trades currently threaten
many species of orchids, parrots, and reptiles.
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Preserving Biodiversity
• Programs have been developed to help us use
species in a way that does not threaten their
survival.
• Certification programs: Organizations such as
the Forest Stewardship Council (FSC) and the
Marine Stewardship Council determine whether
commercial operations harvest and market their
products in ways that meet their criteria.
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Preserving Biodiversity
• The Convention on International Trade in
Endangered Species (CITES), an international
organization, determines and prohibits trade in
endangered species or their products (e.g., whale
meat, rhinoceros horn, many parrots and orchids).
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Preserving Biodiversity
• Many species depend on particular patterns of
disturbance to persist.
• Humans often try to control such disturbances,
but conservation biologists try to determine where
disturbances should be reestablished.
• For example, annual growth rings on ponderosa
pines show that low-intensity fires were once
common in New Mexico.
• Because of sheep grazing and fire suppression,
buildup of dead branches and needles has
resulted in intense, tree-consuming fires.
• Today ground fires are deliberately started to
imitate historic patterns.
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Preserving Biodiversity
• If Earth warms as predicted, climatic zones won’t
just shift. New climates will develop and some
existing climates will disappear.
• New climates are likely to develop at low
elevations in the tropics. A warming of even 2°C
would result in climates that are warmer than any
that exist today.
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Habitat Restoration and Species Recovery
• The field of restoration ecology has developed
to study methods of restoring natural habitats.
• Some damaged habits will not recover without
assistance, and biologists try to maintain some
endangered species in captivity until suitable
habitat is available.
• Conservation biologists have only a limited ability
to restore natural ecosystems and many attempts
have been only partially successful.
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Habitat Restoration and Species Recovery
• Wetland restoration is a high priority in southern
California, where 90 percent of the coastal
wetlands have been destroyed..
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Habitat Restoration and Species Recovery
• Threatened species can sometimes be
maintained in captivity while external threats to
their existence are reduced or removed.
• Captive propagation is a temporary measure,
however, because zoos, aquariums, and botanical
gardens have only a limited capacity.
• Some species have benefited from captive
breeding programs.
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Habitat Restoration and Species Recovery
• Captive breeding is helping to save the California
condor..
• Captive breeding was initiated in 1983 and by 1993
the captive breeding population was 60 birds.
• As of 2003 there were 81 wild condors in California
and Arizona.
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Healing Biotas: Conservation Medicine
• On land and sea, diseases among wild organisms
are threatening biodiversity.
• In parts of the Hawaiian Islands, nearly all
endemic bird species have been eliminated by
avian malaria introduced into the island by exotic
birds.
• The West Nile bird virus has exploded across the
U.S. and has spread to humans.
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Healing Biotas: Conservation Medicine
• A new field of conservation medicine is
developing to help identify the causes of
increases in wildlife diseases and to devise ways
to prevent transmission and limit the effects.
• Molecular techniques are used to identify species,
strains, and life cycles of pathogens.
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Setting Limits: The Legacy of Samuel Plimsoll
• In the nineteenth century, Samuel Plimsoll, an
English MP, persuaded Parliament to require a
“load line” on the hull of every merchant ship to
prevent overloading and thus to reduce the rate of
shipwreck.
• The increasing loss of Earth’s species suggests
that we need such a “Plimsoll line” to limit the load
of human activities on the planet.