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Biodiversity and
Conservation Biology
55
BIOLOGICAL SCIENCE
FOURTH EDITION
SCOTT FREEMAN
Lectures by Stephanie Scher Pandolfi
© 2011 Pearson Education, Inc.
Key Concepts
Biodiversity is quantified at the level of allelic diversity, species
diversity, and ecosystem diversity.
According to recent analyses, the sixth mass extinction in the
history of life is occurring due to habitat loss, overexploitation,
and global climate change.
Humans depend on biodiversity for the products that wild species
provide and for ecosystem services that protect the quality of the
abiotic environment.
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Key Concepts
Solutions to the biodiversity crisis include protecting key habitats,
lowering human population growth and resource use, restoring
ecosystems, mitigating climate change, and supporting sustainable
development.
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Introduction
• The species and resources on our planet are limited, but the human
population is growing unchecked.
• Biologists fear that this surge in human population will drastically
affect biodiversity.
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What Is Biodiversity?
• Biodiversity can be thought of as the tree of life, which describes
the evolutionary relationships among all forms of life. The branches
represent all of the lineages of organisms living today and the tips
represent all of the species.
• When biodiversity increases, branches and tips are added to the
tree. When extinctions occur, tips and perhaps branches are
removed.
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Measuring and Analyzing Biodiversity
To get a complete understanding of the diversity of life, biologists
recognize and analyze biodiversity at the genetic, species, and
ecosystem level.
• Genetic diversity is the total genetic information contained
within all individuals of a species, measured as the number and
relative frequency of all alleles present in a species.
• Species diversity is the variety of life-forms on Earth, measured
as the number and relative frequency of species in a particular
region.
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Measuring and Analyzing Biodiversity
– Recent efforts to document species diversity have used a new
technique called bar coding: the use of a well-characterized
gene sequence to identify distinct species, using the
phylogenetic species concept.
• Taxonomic diversity, an additional aspect of species diversity, is
important because some lineages on the tree of life are extremely
species rich while other lineages are extremely species poor.
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Measuring and Analyzing Biodiversity
• Ecosystem diversity is the variety of biotic communities in a
region, along with abiotic components such as soil, water, and
nutrients.
• Attempts to measure ecosystem diversity focus on capturing the
array of biotic communities and the variation of physical conditions
in a region.
• Biodiversity is dynamic—it has been changing since life on Earth
began.
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Change through Time
• Biodiversity can be recognized and quantified on several distinct
levels, but it is also dynamic.
– Mutations that create new alleles increase genetic diversity;
natural selection, genetic drift, and gene flow may eliminate
certain alleles or change their frequency, leading to an increase
or decrease in overall genetic diversity.
– Speciation increases species diversity; extinction decreases it.
– New ecosystems may form as a result of changes in abiotic
conditions; disturbances, on the other hand, can destroy
ecosystems.
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How Many Species Are Living Today?
• Approximately 1.5 million species have been cataloged to date, but
this represents only a tiny fraction of the number actually present.
• Two general approaches have been used to estimate the total
number of species:
1. Surveys of species-rich groups at small sites (taxon-specific
surveys).
2. Surveys of all the species present in a particular region (alltaxa surveys).
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Taxon-Specific Surveys
• Researchers estimated the number of insect species living in the
canopy of a single tropical tree. They identified over 900 species of
beetles alone.
• From these data, they estimated that the world total of arthropod
species exceeds 30 million species.
• More recently, a taxon-specific survey of marine mollusks
identified 2738 species, supporting the hypothesis that the 93,000
known mollusk species may represent just a third to a half of the
actual total.
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All-Taxa Surveys
• The first effort to find and catalog all of the species present in a
large area, the Great Smoky Mountains National Park, is now under
way.
• The survey started in 1999 and will be finished in 2015.
• To date, over 890 new species, and over 6300 species that had
never before been found in the park, have been discovered.
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Where Is Biodiversity Highest?
• In most taxonomic groups, species richness is highest in the tropics
and declines toward the poles.
• The tropical rain forests are particularly species rich. Even though
they represent just 7 percent of Earth’s land area, they are thought
to contain at least 50 percent of all species present.
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Hotspots of Biodiversity and Endemism
• Biodiversity hotspots are regions that are much more species rich
than others.
• In addition, some regions of the world have a high proportion of
endemic species—species that are found in a particular area and
nowhere else.
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Conservation Hotspots
• Biologists are studying the geographic distribution of biodiversity
as a way of focusing conservation efforts.
• Conservation hotspots are regions that contain at least 1500
endemic plant species and from which at least 70 percent of the
traditional or primary vegetation has been lost.
• These conservation hotspots are areas that are in most urgent need
of conservation action and where efforts to preserve habitat would
have the highest return on investment.
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Threats to Biodiversity
• Although extinction is natural, the rates of extinction are increasing.
Today, species are vanishing faster than at virtually any other time
in Earth’s history. Modern rates of extinction are 100 to 1000 times
greater than the average, or “background,” rate recorded in the
fossil record over the past 550 million years.
• Directly or indirectly, recent extinctions are being caused by human
population growth.
• Most biologists agree that the sixth mass extinction in the history of
multicellular life is now under way.
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Changes in the Nature of the Problem
• Most extinctions that have occurred over the past 1000 years took
place on islands as the result of overhunting or introduction of
exotic species—nonnative competitors, diseases, or predators.
• Fossil evidence on islands in the South Pacific suggests that about
2000 bird species were wiped out as people colonized this area
around A.D. 1200.
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© 2011 Pearson Education, Inc.
Changes in the Nature of the Problem
• Starting in the twentieth century, though, two patterns in species
loss began to change:
1. Endangered species, species that are almost certain to go
extinct without effective conservation programs, are now
more likely to live on continents than on islands.
2. Habitat destruction has replaced overhunting and introduction
of exotic species as the primary threat to such species
worldwide.
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Changes in the Nature of the Problem
• Recent analysis of causes of endangerment for 488 endangered
species native to Canada show several patterns:
1. Habitat loss is the single most important factor in the decline
of these species.
2. Virtually all of the endangered species are affected by more
than one factor.
3. Overharvesting is the dominant problem for marine species,
while pollution plays a large role for freshwater species.
4. Factors beyond human control can also be important.
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Changes in the Nature of the Problem
• Although invasive species are a major problem in some regions,
most analyses completed to date are broadly consistent with the
Canadian data.
• Overhunting has also emerged recently as a dire threat to many
mammal populations in Africa and southeast Asia.
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Habitat Destruction
• Humans cause habitat destruction in many ways, from logging
and burning forests, to grazing livestock, filling in wetlands, and
building housing developments.
• On a global scale, one of the most important types of habitat
destruction is deforestation. As many as 3 million hectares (ha)
have been deforested each year in the Amazon in the 1990s.
• The global rate of deforestation has now slowed compared with
these rates, but as of 2005, 7.3 million ha/year are still being lost.
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Habitat Destruction
• The total area of wet tropical forest dropped by 2.36 percent during
2000–2005.
• If this rate of tropical deforestation continues, over 28 percent of
the wet tropical forest that exists today will be gone in your
lifetime, including almost half of the Brazilian Amazon.
• Forest loss in South America and Africa is particularly important
because it is occurring in biodiversity hotspots.
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Habitat Fragmentation
• Human activities also result in habitat fragmentation—the
breakup of large, contiguous areas of natural habitat into small,
isolated pieces.
• Habitat fragmentation concerns biologists for several reasons:
1. Habitat fragmentation can reduce habitats to a size that is too
small to support some species.
2. Fragmentation reduces the ability of individuals to disperse
from one habitat to another. Small, isolated populations may
be more vulnerable to catastrophes, and can suffer from
inbreeding depression and loss of alleles due to genetic drift.
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Habitat Fragmentation
3. Fragmentation creates large amounts of “edge” habitat. These
fragmented habitats can suffer a rapid loss of species diversity
and a startling drop in biomass.
• When habitats are fragmented, the quality and quantity of habitat
decline drastically.
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Habitat Fragmentation
• A long-term experiment in a tropical wet forest is documenting the
decline in habitat quality caused by fragmentation.
• Plots of different sizes were shown to have a rapid loss of species
diversity, especially from the smaller fragments; and a startling
drop in biomass, or the total amount of fixed carbon, in the study
plots located near the edges of logged fragments.
• This experiment demonstrates that when habitats are fragmented,
the quality and quantity of habitat decline drastically.
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Habitat Fragmentation
Web Activity: Habitat Fragmentation
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Problems in Small Populations
• The small, isolated populations that make up a metapopulation are
more likely than large populations to be wiped out because:
1. Stochastic—chance—catastrophic events such as storms,
disease outbreaks, or fires exterminate small populations
more readily than large populations.
2. Small populations suffer from inbreeding depression and
random loss of alleles due to genetic drift.
• Fitness declines in small, isolated populations can be documented
by experimentally increasing gene flow; introducing new alleles
may counteract the effects of genetic drift and inbreeding.
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Climate Change
• Climate change might change extinction rates:
1. Loss of coral reefs due to high-temperature-induced
“bleaching.”
2. Loss of habitat for species native to arctic and alpine tundras.
3. Trees and other slowly dispersing species are unable to track
changes in climate.
4. Ocean acidification—due to increased carbon dioxide
concentrations—inhibit the ability of marine animals to make
calcium carbonate skeletons.
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Can Biologists Predict Future Extinction Rates?
• To estimate current extinction rates and predict how they might
change in the near future, biologists use two approaches:
1. Direct counts of extinct species.
2. Using species–area relationships to predict the consequences
of habitat destruction.
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Estimates Based on Direct Counts
• The best information on current extinction rates comes from studies
on birds.
• Recent analyses suggest that birds have been going extinct at a rate
100 times the background rate, or at a rate of one species per year
rather than one species per 100 years. This rate is also expected to
increase.
• Similar trends are occurring in other well-studied groups.
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Species–Area Relationships
• Biologists can use habitat-loss projections to estimate rates of
extinction based on well-documented species–area relationships.
• Over many different habitat types, the relationship is consistently
described by the function S = cAz, where S is the number of species,
c is a constant that is high in species-rich areas and low in speciespoor areas, A is habitat area, and z is the slope of the line on a loglog plot of species number versus area.
• Thus, z describes how rapidly species numbers change with area.
Typically, z is about 0.25. When z is higher, more species are
predicted to be lost.
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Why Is Biodiversity Important?
• Biodiversity has both economic and biological benefits.
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Economic Benefits of Biodiversity
• Wild species have provided the raw material to fuel the
development of human societies ever since the first large-scale,
highly organized cultures began to develop about 10,000 years ago:
– Plants yield food and fiber.
– Animals provide food, labor, and material goods.
– Protein can be harvested from the oceans.
– Plants, animals, and fungi can be processed as sources of
medicines.
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Economic Benefits of Biodiversity
• The direct use of biodiversity continues today:
– Seed banks—long-term storage facilities—are used to preserve
diverse strains of crop plants.
– Insect-pollinated crops produce $40 billion worth of products
annually.
– Bioprospecting research focuses on assessing different
organisms as novel sources of drugs or ingredients in consumer
products.
– In bioremediation, organisms are used to metabolize pollutants
and render them harmless.
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Economic Benefits of Biodiversity
– Recreation based on visiting wild places, or ecotourism, is a
major industry internationally and is growing rapidly.
– Vegetation on steep slopes and wetlands in low-lying areas
dramatically reduces flood damage and the danger posed by
mudslides.
In addition, the benefits of biodiversity extend beyond the direct
use of diverse genes and species by humans to include ecosystem
services―processes that increase the quality of the abiotic
environment.
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Biological Benefits of Biodiversity
• The productivity of ecosystems depends on the number and type of
species present, or the biodiversity.
• Species richness has a positive impact on net primary
productivity (NPP), the total amount of photosynthesis per unit
area per year that ends up in biomass.
• This may be due to resource-use efficiency, facilitation, and
sampling effects.
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Biodiversity Increases Productivity
• Follow-up experiments in an array of ecosystems not only
supported the conclusion that species richness has a positive impact
on NPP, but showed that several causal mechanisms may be at
work:
– Resource use efficiency—when species diversity is high, more
overall water is used and more photosynthesis can occur.
– Facilitation—certain species facilitate the growth of other
species by providing them with nutrients, partial shade, or other
benefits.
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Biodiversity Increases Productivity
– Sampling effects—in many habitats one or two species are
extremely productive. Simply due to sampling, high-species
plots will tend to outproduce low-species plots.
• The three mechanisms are not mutually exclusive—several can
operate at the same time.
• Long-term experiments have shown that the reason for the pattern
can change over time.
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Does Biodiversity Lead to Stability?
• The stability of a community refers to its ability to do the
following:
1. Withstand a disturbance without changing.
2. Recover to former levels of productivity or species richness
after a disturbance.
3. Maintain productivity and other aspects of ecosystem function
as conditions change over time.
• Resistance is a measure of how much a community is affected by a
disturbance.
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Does Biodiversity Lead to Stability?
• Resilience is a measure of how quickly a community recovers
following a disturbance.
• Communities that are more diverse appear to be more productive,
more resistant to disturbance and invasion, and more resilient than
communities that are less diverse.
• Increased species richness increases the services provided by
ecosystems.
• If ecosystems are simplified by extinctions, productivity and other
attributes might decrease.
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Preserving Biodiversity
• The conservation of biodiversity is urgent because, unlike other
environmental problems, extinction is irreversible.
• The only solution to the biodiversity crisis is to prevent the loss of
alleles, species, and ecosystems.
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Designing Effective Protected Areas
• Biologists joined with government agencies, economists,
community leaders, private landowners, and others to set aside
protected areas.
• So far, 11.5 percent of Earth’s terrestrial surface has been set aside
as protected areas.
• Researchers are using a geographic approach called the Gap
Analysis Program (GAP) to assess the effectiveness of the current
system of protected areas.
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Gap Analysis Program
• The Gap Analysis Program (GAP) identifies gaps between
geographic areas that are particularly rich in biodiversity and areas
that are actually managed for the preservation of biodiversity.
• One recent GAP analysis combined data sets on the distribution of
mammals, birds, amphibians, and freshwater turtles with a map of
world protected areas. The analysis revealed that the ranges of
many species occur completely outside any protected areas.
• Most GAP analyses suggest that the 11.5 percent of Earth’s surface
area that is now being managed for biodiversity will not be enough
to conserve many species.
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Designing Effective Protected Areas
• To connect populations that would otherwise be isolated, wildlife
corridors are being created.
• The goals of these corridors are:
1. To allow areas to be recolonized if a species is lost in a
particular area.
2. To introduce new alleles that would counteract the deleterious
effects of inbreeding and genetic drift.
• Experimental evidence suggests that wildlife corridors are effective.
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Beyond Protected Areas: A Comprehensive Approach
• Given the magnitude of the current extinction rate, the continued
growth in human population size and resource use, and the
difficulty of setting up enough preserved areas in the world’s
conservation hotspots, conservation biologists are advocating a
multipronged strategy.
Preserving land will not be enough. At least four other strategies
need to be an important part of a lasting solution to the biodiversity
crisis.
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Sustainable Development
• In almost every case, the underlying causes of the biodiversity
crisis are socioeconomic factors that encourage the short-term
overexploitation of land and other resources and discourage longterm sustainability.
• Sustainability is the managed use of resources at a rate no faster
than the rate at which they are replaced.
• The challenge is to create ways for humans to live off the resources
that are being produced continuously on Earth, rather than mining
resources that have been stored for centuries or millennia.
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Stabilizing Human Population Size and Resource Use
• Most biologists recognize that it may be impossible to preserve
high species diversity and high-functioning ecosystems if:
1. The human population grows to 13 billion or more over the
next century; and
2. Individuals in the industrialized nations continue to use fossil
fuels and other resources at the current rate.
• Efforts to limit family size and resource use are critical to solving
the biodiversity crisis.
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Ex Situ Conservation
• One approach to coping with impending extinctions is referred to as
ex situ conservation—the preservation of species in zoos, aquaria,
wildlife ranches, seed banks, or other artificial settings.
• Some species—including Pere David’s deer, Przewalski’s horse,
and the Arabian oryx—are extinct in the wild and exist only in
captivity.
• In other cases, captive breeding and reintroduction programs have
succeeded in creating wild populations of endangered species.
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Ecosystem Restoration
• In many areas of the world, ecosystems are already heavily
degraded or lost.
• Thousands of large-scale and small-scale ecosystem restoration and
reforestation projects are now occurring around the globe.
• In 2004, Wangari Maathai won the Nobel Peace Prize to honor her
work founding the Green Belt Movement—a reforestation
organization that has now sponsored the planting of over 1 billion
trees, beginning in Kenya and expanding internationally.
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Ecosystem Restoration
• One of the most successful ecological restoration efforts focused on
the seasonally dry forest at the Area de Conservación Guanacaste in
northwestern Costa Rica.
• The primary task was to stop human-caused fires.
• Their efforts since the mid-1980s have succeeded in transforming a
vast swath of marginally productive ranching land into an
increasingly popular ecotourist destination and a water source for
neighboring farms and ranches.
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A Case History: The Malpai Badlands
• In response to threats from development, a group of ranchers
banded together to form an association they called the Malpai
Borderlands group. To preserve biodiversity and their livelihood,
the ranchers:
– Protected 42,000 acres of their land with conservation
easements.
– Set up cooperative “grassbanks,” available to ranchers whose
own grazing areas are suffering from short-term drought.
– Reintroduced fire to the area via prescribed burns, which
removes encroaching woody shrubs and encourages the growth
of native grasses.
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A Case History: The Malpai Badlands
• Today, the Malpai Borderlands group is considered a model of
innovative action by private individuals, in cooperation with
governmental agencies and nongovernmental organizations.
– The project benefits local people as well as biodiversity.
• It can be done. Your generation is facing the most serious global
environmental crisis in the history of our species. The decisions you
make, ranging from how many children you have to how much you
drive a car, will have far-reaching consequences.
• Change happens one person at a time.
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