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CHAPTER 20
Human Impact on the
Environment
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society:
Aquarium Menaces
• In May 2002, a fisher in Maryland caught and
released an exotic looking fish, which was
identified as the northern snakehead.
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Figure 20.1a
• The northern snakehead
– Is a fish native to eastern Asia.
– Was accidentally introduced into Maryland.
• Introduced species
– Can severely disrupt ecosystems.
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• The seaweed Caulerpa
– Was accidentally introduced into the United
States, probably after being dumped from a home
aquarium.
– Has caused significant problems and competes
with native species.
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Figure 20.1b
Human Impact on Biological Communities
• Human disturbance of biological communities is
almost always destructive.
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Human Disturbance of Communities
• Of all animals, humans have the greatest impact on
communities worldwide.
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Figure 20.2
• Much of the United States is now a hodgepodge of
early successional growth where more mature
communities once prevailed.
• Human disturbance usually reduces species
diversity in communities.
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Introduced Species
• Introduced species
– Are those that humans intentionally or
accidentally move from the species’ native
locations to new geographic regions.
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• Kudzu, a Japanese plant
– Was introduced into the United States in 1930 as
a means of erosion control.
– Has taken over vast expanses of the southern
landscape.
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Figure 20.3a
• The European starling
– Was introduced into the United States by a group
intent on introducing all the plants and animals
mentioned in Shakespeare’s plays.
– Has displaced many native songbirds.
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Figure 20.3b
• Argentine ants
– Were accidentally introduced into the United
States.
– Have decimated populations of native ants in
California.
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Figure 20.3c
• The zebra mussel
– Was accidentally introduced into the United
States, probably in ballast water from a cargo
ship.
– Has caused significant problems and competes
with native species.
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Figure 20.3d
Human Impact on Ecosystems
• Human population growth and technology add up
to a badly bruised biosphere.
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• The carbon dioxide exhaust of our machinery
– Is probably causing a global warming that will
affect all life on Earth.
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Figure 20.4
Impact on Chemical Cycles
• Human activities
– Often intrude in biogeochemical cycles by
removing nutrients from one location and adding
them to another.
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Impact on the Carbon Cycle
• The increased burning of fossil fuels
– Is steadily raising the level of CO2 in the
atmosphere.
– Is leading to significant environmental problems,
such as global warming.
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Impact on the Nitrogen Cycle
• Sewage treatment facilities and fertilizers
– Add large amounts of nitrogen to aquatic systems,
causing heavy growth of algae.
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Impact on the Phosphorous Cycle
• Sewage treatment facilities and fertilizers
– Also add large amounts of phosphates to aquatic
systems, causing eutrophication of lakes.
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Figure 20.5
Impact on the Water Cycle
• Destruction of tropical rain forest
– Will change the amount of water vapor in the air.
– May alter local and global weather patterns.
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Figure 20.6
• To irrigate crops, humans pump large amounts of
ground water to the surface.
• Deforestation and extensive removal of ground
water change the water cycle.
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The Process of Science: Does Deforestation Change
Chemical Cycles?
• The Hubbard Brook Experimental Forest is a study
site for chemical cycling in a forest ecosystem.
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• Researchers have monitored water and mineral loss
by damming parts of a creek in the forest.
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Figure 20.7a
• One valley was completely deforested,
– And the inflow and outflow of water and minerals
was compared to a control area.
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Figure 20.7b
• Net losses of minerals from the altered area were
huge, exhibiting the impact of human activity on a
forest ecosystem.
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Figure 20.7c
The Release of Toxic Chemicals to Ecosystems
• Humans have added to ecosystems new toxic
materials, which often cannot be degraded by
microorganisms.
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• Toxic substances
– Are acquired by organisms from the environment
along with nutrients and water.
– May be metabolized, but can also accumulate in
specific tissues.
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• Biological magnification
– Is a process in which toxins become more
concentrated in successive trophic levels of a food
web.
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Figure 20.8
Human Impact on the Atmosphere and Climate
• It was once thought that the atmosphere could
absorb the variety of gaseous waste products
produced by humans.
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Figure 20.9
Carbon Dioxide Emissions, the Greenhouse Effect,
and Global Warming
• Since the Industrial Revolution, the concentration
of CO2 in the atmosphere has been increasing due
to the burning of fossil fuels and wood and to
deforestation.
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Figure 20.10
• The greenhouse effect
– Retains solar heat in the atmosphere.
– Is produced by CO2 and water vapor in the
atmosphere.
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Figure 20.11
• The marked increase in atmospheric CO2 could
cause an increase in global temperatures, with
potentially disastrous consequences.
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• Developed countries
– Have the greatest energy consumption.
– Have the greatest responsibility to reduce energy
consumption.
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Depletion of Atmospheric Ozone
• The ozone layer
– Absorbs UV radiation, preventing much of it from
contacting organisms in the biosphere.
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• The protective ozone layer
– Has been thinning since 1975 because of the
accumulation of chlorofluorocarbons.
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Figure 20.12
• The consequences of ozone depletion
– May be quite severe for all life on Earth,
including humans.
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The Biodiversity Crisis
• The effect of human activity on communities and
ecosystems is an alarming biodiversity crisis, a
precipitous decline in Earth’s great variety of life.
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The Three Levels of Biodiversity
• Biodiversity has three main components.
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• The first is the diversity of ecosystems.
• The second is the variety of species that make up
the biological community of any ecosystem.
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Figure 20.13
• The third is the genetic variation within each
species.
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The Loss of Species
• The current mass extinction
– Is being caused by human activity.
– Is broader and faster than other past extinctions.
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• We do not know the full scale of the biodiversity
crisis.
– However, there are enough signs to know that the
biosphere is in deep trouble.
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• 12% of the known bird species in the world and
24% of the known mammal species are threatened
with extinction.
• Of the 20,000 known plant species in the United
States, 200 have become extinct and 730 are
endangered or threatened.
• About 20% of the known freshwater fishes in the
world have become extinct or are seriously
threatened.
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• Biologist Edward O. Wilson has compiled the
Hundred Heartbeat Club, which includes species of
animals that number fewer than a hundred
individuals.
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Figure 20.14
• Several researchers estimate that at the current rate
of destruction, over half of all plant and animal
species will be gone by the end of the 21st century.
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The Three Main Causes of the Biodiversity Crisis
Habitat Destruction
• Human alteration of habitat
– Poses the single greatest threat to biodiversity
throughout the biosphere.
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Figure 20.15a
Introduced Species
• Human introduction of exotic species
– Ranks second behind habitat loss.
– Can cause rapid extinctions.
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Figure 20.15b
Overexploitation
• Overexploitation of wildlife
– Is the third major threat to biodiversity.
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Figure 20.15c
Why Biodiversity Matters
• Humans rely on biodiversity for
– Food, clothing, shelter.
– Oxygen, soil fertility, medicinal substances.
• Endemic species
– Are those found nowhere else.
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Figure 20.16
• The loss of diversity
– Limits the potential for new discoveries of food
and medicine.
– Reflects large-scale changes in the biosphere that
could have catastrophic consequences.
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Conservation Biology
• Conservation biology
– Is a goal-oriented science that seeks to counter the
loss of biodiversity.
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Biodiversity “Hot Spots”
• A biodiversity hot spot
– Is a relatively small area with an exceptional
concentration of species.
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Figure 20.17
• Endemic species
– Are often found in hot spots.
– Are highly sensitive to habitat degradation.
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• Some biologists
– Estimate that loss of habitat will cause the
extinction of about half the species in hot spots.
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Conservation at the Population and Species Levels
• Much of the discussion of the biodiversity crisis
centers on species.
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• The U.S. Endangered Species Act
– Defines an endangered species as one that is “in
danger of extinction throughout all or a significant
portion of its range.”
– Defines a threatened species as one likely to
become endangered in the foreseeable future.
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Habitat Fragmentation and Subdivided Populations
• Population fragmentation
– Is the splitting and consequent isolation of
portions of populations by habitat degradation.
– Is one of the most harmful effects of habitat loss
due to human activities.
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Figure 20.18
• Fragmentation usually results in
– A decrease in the overall size of populations.
– A reduction in gene flow among subpopulations.
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• Subpopulations
– Are separated into habitat patches that vary in
quality.
• A source habitat
– Is one of good quality where a subpopulation’s
reproductive success exceeds it death rate.
– Can produce enough individuals that some
disperse to other areas.
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• A sink habitat
– Is one of poor quality where the subpopulation’s
death rate exceeds its reproductive success.
• Dispersal of individuals to sink habitats because of
habitat loss can sometimes threaten the survival of
subpopulations in source habitats.
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What Makes a Good Habitat?
• Identifying the specific combination of habitat
factors that is critical for a species is fundamental
to conservation biology.
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• The red-cockaded woodpecker
– Provides a case study in identifying critical
habitat factors.
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Figure 20.19a
• Certain habitat factors are necessary for these
birds:
– Mature pines and low growth of plants
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Figure 20.19b
• A habitat that has become a sink has thick and tall
undergrowth.
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Figure 20.19c
Conserving Species amid Conflicting Demands
• Conservation biology
– Often highlights the relationships between
biology and society.
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• Competing demands for habitat are almost always
an issue.
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Conservation at the Ecosystem Level
• Conservation biology
– Increasingly aims at sustaining the biodiversity of
entire communities and ecosystems.
• Landscape ecology
– Is the application of ecological principles to the
study of land-use patterns.
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Edges and Corridors
• Edges between ecosystems
– Are prominent features of landscapes.
– Can be natural.
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Figure 20.20a
– Can be created by humans.
– Can have both positive and negative effects on
biodiversity.
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Figure 20.20b
• A movement corridor
– Is a narrow strip or series of small clumps of
quality habitat connecting otherwise isolated
patches.
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Figure 20.21
• Corridors
– Can promote dispersal and help sustain
populations.
– Are especially important to species that migrate
between different habitats seasonally.
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Zoned Reserves
• A zoned reserve
– Is an extensive region of land that includes one or
more areas undisturbed by humans.
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Figure 20.22a
• The areas surrounding zoned reserves
– Continue to be used to support the human
population, but they are protected from extensive
alteration.
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Figure 20.22b
The Goal of Sustainable Development
• Sustainable development
– Balances human needs with the health of the
biosphere.
• The goal of sustainable development
– Is the long-term prosperity of human societies and
the ecosystems that support them.
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• Some ways to promote sustainability
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Table 20.1
Evolution Connection:
Biophilia and an Environmental Ethic
• Edward O. Wilson makes the case that biophilia,
the human desire to affiliate with other life in its
many forms, is innate.
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Figure 20.23
• Most biologists
– Have embraced the concept of biophilia.
– Have turned their passion for nature into careers.
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Figure 20.24