Download Table of Contents - Milan Area Schools

Conservation Biology
57
Conservation Biology
• Introduction
• Why Care about Species Extinctions?
• Estimating Current Rates of Extinction
• Preserving Biodiversity
• Habitat Restoration and Species Recovery
• Healing Biotas: Conservation Medicine
• Setting Limits: The Legacy of Samuel Plimsoll
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.
57
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.
57
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.
57
Why Care about Species Extinctions?
• In Western Cape Province, South Africa,
preservation of the native ecosystem is vital to
maintaining the water supply of the area.
• The native vegetation of the highlands is a
species-rich community of shrubs called fynbos
that can survive drought, nutrient-poor soils, and
fire. The highlands provide two thirds of Western
Cape’s water.
• The fynbos also provides income in the form of
cut flowers and tourism.
• The native vegetation is being displaced by
introduced plants that grow taller and faster,
increase the intensity of fires, and reduce the
water supply.
Figure 57.1 Invasive Species Disrupt Ecosystem Function (Part 1)
Figure 57.1 Invasive Species Disrupt Ecosystem Function (Part 2)
Figure 57.1 Invasive Species Disrupt Ecosystem Function (Part 3)
57
Why Care about Species Extinctions?
• By removing the exotic plants and managing fire,
the natural fynbos ecosystem can be preserved.
• High-tech approaches to replacing water (such as
sewage purification plants and desalinization)
would cost between 1.8 and 6.7 times as much as
maintaining natural vegetation in the watershed.
57
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.
57
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.
57
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.
• A 12-year study of grizzly bears in Yellowstone
National Park suggested that for the bears to have
a 95% chance of survival for 100 years, there must
be habitat to support 70–90 bears.
• To achieve a higher probability of survival, or
survival for a longer time, more bear habitat would
be needed.
57
Preserving Biodiversity
• The human activities that threaten species include
habitat destruction, introduction of invasive
species, overexploitation, disease, alteration of
disturbance patterns, and climate change.
• Conservation biologists determine how these
activities are affecting species and devise
strategies to preserve endangered or threatened
species.
57
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.
Figure 57.2 Proportions of U.S. Species Extinct or in Peril
57
Preserving Biodiversity
• The fraction of a habitat patch that is influenced
by adjacent habitat conditions (edge effects)
increases rapidly as patch size decreases.
• Close to the edges of a forest patch, for example,
the environment differs from that inside the forest,
so species from surrounding habitats colonize the
edges to compete with or prey upon those inside.
Figure 57.3 Edge Effects
57
Preserving Biodiversity
• Usually it is not known which organisms lived in
an area before their habitats became fragmented.
• A major research project in Manaus, Brazil, was
undertaken to examine the effects of habitat
fragmentation.
• Landowners agreed to preserve forest patches of
certain sizes and configurations.
• Biologists examined species diversity before and
after logging around the patches.
• Species began to disappear from the isolated
patches soon after the surrounding forest was cut.
Figure 57.4 Brazilian Forest Fragments Studied for Species Loss
57
Preserving Biodiversity
• Species that become extinct in small patches are
unlikely to be reestablished, but corridors between
patches can allow individuals to disperse and
species to persist.
• In Brazil, within 7–9 years of having abandoned
the logged patches, birds reestablished
themselves in the young forest that grew up.
57
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.
57
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.
57
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.
• Australia and New Zealand require a weed risk
assessment for the importation of plants.
57
Preserving Biodiversity
• The U.S. horticultural industry has crafted a
voluntary code of conduct stating that the invasive
potential of a plant should be assessed prior to its
introduction and marketing.
• A decision tree can be used to determine whether
a species is likely to become invasive.
• A plant species is more likely to become invasive
if it has short generation time, small seeds, a
large range, and no evolutionary relationship to
plants in the new area.
• Conservation biologists have developed a
decision tree to determine whether exotic species
can safely be introduced into North America.
Figure 57.5 A “Decision Tree” to Govern Introductions (Part 1)
Figure 57.5 A “Decision Tree” to Govern Introductions (Part 2)
57
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.
57
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.
57
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).
57
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.
Figure 57.6 The Frequency and Intensity of Fires Affect Ecosystems
57
Preserving Biodiversity
• Atmospheric scientists predict that average
temperatures in North America will increase 2–
5°C by the end of the century.
• Species will need to shift their ranges as much as
500–800 km. Some habitats, such as alpine
tundra, may disappear.
• Knowledge of how organisms responded to past
climate changes, such as postglacial warming,
can help us predict the effects of the current
warming.
• Organisms such as birds, which have good
dispersal abilities, can shift their ranges rapidly.
57
Preserving Biodiversity
• Other species shift ranges much more slowly.
• In North America, some species of coniferous
trees expanded northward as glaciers retreated.
• Earthworms disperse very slowly. Introduced
earthworms from Europe are able to survive in
places north of the current distribution of native
earthworms.
• Slow dispersal, not lack of suitable habitat, has
kept native earthworms from moving northward.
Figure 57.7 Some Species Shift Their Ranges in Response to Climate Change (Part 1)
Figure 57.7 Some Species Shift Their Ranges in Response to Climate Change (Part 2)
57
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.
• In 1988, the highest sea surface temperatures
ever recorded caused corals to undergo
bleaching and increased their mortality
worldwide.
Figure 57.8 Global Warming Affects Corals (Part 1)
Figure 57.8 Global Warming Affects Corals (Part 2)
57
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.
57
Habitat Restoration and Species Recovery
• Wetland restoration is a high priority in southern
California, where 90 percent of the coastal
wetlands have been destroyed.
• In early attempts at species restoration, many
species failed to recolonize the wetlands.
• Biologists discovered that the problem was lack of
diversity in the plant species introduced. Plots
later planted with species-rich mixtures developed
the complex vegetation needed for birds and
insects and accumulated nitrogen more quickly
than the species-poor experimental communities.
Figure 57.9 Species Richness Enhances Wetland Restoration (Part 1)
Figure 57.9 Species Richness Enhances Wetland Restoration (Part 2)
57
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.
57
Habitat Restoration and Species Recovery
• Captive breeding is helping to save the California
condor.
• The condor once ranged from British Columbia to
Mexico, but by 1978 the wild population was down
to about 30 birds.
• Captive breeding was initiated in 1983 and by 1993
the captive breeding population was 60 birds.
• Captive-bred birds were released in California and
Arizona and were found to use the same roosting
sites, bathing pools, and mountain ridges as their
predecessors.
• As of 2003 there were 81 wild condors in California
and Arizona.
Figure 57.10 Soaring High Once More
57
Healing Biotas: Conservation Medicine
• On land and sea, diseases among wild organisms
are threatening biodiversity.
• The Caribbean Basin and seas in the Indo-Pacific
have lost corals and other organisms.
• 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.
Figure 57.11 Extinct Hawaiian Honeycreepers
57
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.
57
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.