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Human Impact on the Environment
CHAPTER 20 Human Impact on the Environment
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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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 20.1a
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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
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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
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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
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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
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Argentine ants Were accidentally introduced into the United States.
Have decimated populations of native ants in California.
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Figure 20.3c
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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
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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
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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
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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
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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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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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
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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
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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
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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
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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
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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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 20.10
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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
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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
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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
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The third is the genetic variation within each species.
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The current mass extinction
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
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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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 20.15a
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Human introduction of exotic species
Introduced Species Human introduction of exotic species Ranks second behind habitat loss. Can cause rapid extinctions.
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Figure 20.15b
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Overexploitation of wildlife
Is the third major threat to biodiversity.
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Figure 20.15c
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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
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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
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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
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Fragmentation usually results in
A decrease in the overall size of populations. A reduction in gene flow among subpopulations.
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Subpopulations A source habitat
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
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Certain habitat factors are necessary for these birds:
Mature pines and low growth of plants
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Figure 20.19b
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A habitat that has become a sink has thick and tall undergrowth.
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Figure 20.19c
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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 between ecosystems
Edges and Corridors Edges between ecosystems Are prominent features of landscapes. Can be natural.
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Figure 20.20a
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Can be created by humans.
Can have both positive and negative effects on biodiversity.
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Figure 20.20b
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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
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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
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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
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The Goal of 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
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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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 20.23
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Most biologists Have embraced the concept of biophilia.
Have turned their passion for nature into careers.
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Figure 20.24
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