Mastering Concepts
39.1
1. What is the value of diversity to humans and to ecosystems as a whole?
Humans and ecosystems as a whole depend upon many diverse organisms to survive.
Biodiversity is necessary for the health of Earth’s food chains and food webs (some of
which include humans), maintenance of its biogeochemical cycles, and prevention of
flooding and soil erosion.
2. Describe the three types of biodiversity.
Genetic biodiversity is the amount of genetic variation in a species. Species biodiversity
is the number of species in the biosphere. Ecosystem biodiversity accounts for the
different types of ecosystems on earth.
3. Differentiate among extinct, endangered, and vulnerable species.
Extinct species no longer exist. Endangered species are at high risk for extinction in the
near future, and vulnerable species are likely to become extinct in the distant future.
4. What is conservation biology?
Conservation biology is the study of diversity at all levels, with the goal of understanding
why species go extinct and preventing this outcome.
39.2
1. Which human activities account for most of the loss of terrestrial habitat?
Habitat destruction comes from farming and urban growth, which results in deforestation
and desertification.
2. How do dams and channelization alter river ecosystems?
Dams flood some areas and deprive others of water, and they change the qualities of
water such as its temperature, oxygen content, and nutrient content. Channelization
destroys habits by removing streamside habitat and changing the rate at which water
flows. As water moves more quickly, sediments are flushed further downstream, often
carried many miles to be deposited at the mouth of a river.
3. Why is damage to estuaries especially devastating?
Estuaries are places where larvae and young of many species of sea life shelter and grow
until they can move upstream to rivers or into ocean waters. Damaging estuaries kills
many forms of life at their developmental stages.
39.3
1. How do toxic chemicals, nutrients, sediments, and heat affect aquatic ecosystems?
Toxic chemicals may persist and be biologically magnified as they move up food chains,
eventually causing cancer and disturbing reproduction in some species. Excess nutrients
in an aquatic ecosystem cause eutrophication, which causes O2 depletion and kills many
aquatic organisms. Sediments block the penetration of light and reduce photosynthesis in
aquatic ecosystems. Excess heat reduces the oxygen-carrying potential of water and may
kill aquatic organisms.
2. What are major sources of industrial smog, photochemical smog, and acid deposition?
Major sources of industrial smog include power plants, factories, and households that
burn coal and oil. Photochemical smog comes from emissions from vehicles. Coalburning power plants are major sources of acid deposition.
3. What effects do smog, acid deposition, particulates, and the thinning ozone layer have
on life?
Smog: injures plants and causes human respiratory problems. Acid deposition disrupts
food webs in acidified lakes, killing many species; acid deposition also kills forest trees
and may play a role in die-offs of amphibians. Particulates block photosynthesis; in
humans, they may also trigger inflammation, shortness of breath, asthma, and cancer. The
thinning of the ozone layer allows harmful UV radiation to reach Earth’s surface, causing
an increase in skin cancer and cataracts. UV radiation also kills phytoplankton at the base
of food webs in aquatic ecosystems and may be partly responsible for die-offs of
amphibians.
4. Why is CO2 accumulating in Earth’s atmosphere?
Excess CO2 is accumulating from the burning of fossil fuels and from tropical
deforestation.
5. Describe how and why Earth’s climate changed during the past century.
During the 20th century Earth’s climate changed as the atmospheric concentration of CO2
and average global temperatures have both increased.
6. How does global climate change threaten biodiversity?
Species are adapted to their current environments. Climate change that causes rapid
ecosystem changes may cause many species to go extinct if they cannot migrate to new
areas.
39.4
1. What features characterize an invasive species?
An invasive species breeds easily and spreads widely from its point of introduction; it
also causes damage to the environment.
2. How do invasive species disrupt ecosystems?
Invasive species can prey on other species, reduce the availability of sunlight, destroy the
tissues of native plants or animals, or displace native species.
3. List examples of species declines caused by overexploitation.
Examples of species declines caused by overexploitation include the dodo, passenger
pigeon, Carolina parakeet, commercially fished species such as tuna, flounder, halibut,
swordfish, and cod, and many species that are not targets of commercial fishing, but that
nevertheless are harmed by its practices. These include marine mammals, marine
invertebrates, seabirds, sea turtles, and many species of fishes that are used as food for
farmed salmon and shrimp.
39.5
1. What is the relationship between human population growth and conservation biology?
As the human population grows, it exerts increased pressures on natural resources.
Biodiversity suffers. So, as the human population continues to grow, conservation
biology becomes increasingly important in the attempt to preserve biodiversity.
2. List and describe seven tools that conservation biologists use to preserve biodiversity.
1. Set aside protected habitat. 2. Reverse habitat destruction. 3. Captive breeding and
reintroduction to help increase population numbers. 4. Manage harvests, reducing the
numbers of organisms taken in a year. 5. Predator control. 6. Biotechnology, perhaps to
clone extinct or endangered organisms or to identify undiluted gene pools in the wild. 7.
Develop ecotourism and other economic incentives for preservation.
3. How can scientists, governments, and ordinary citizens work together for
conservation?
Scientists contribute new information about species declines or recovery, and government
policies can influence the actions of individuals and corporations. Ordinary citizens can
support conservation efforts in everyday life.
39.6
1. Summarize the evidence that climate change is a factor in the extinction of harlequin
frogs.
All the extinct species came from the midland elevations where some cloud cover is
normal. Coinciding with the extinctions was a change in climate such that the days were
cooler and the nights warmer, creating a thicker cloud cover. The decrease in sunny
patches may have helped a skin fungus flourish.
2. Other than climate change, what is an alternative hypothesis that could explain that
extinction of harlequin frogs? How would you test your hypothesis?
[Answers will vary]
Write It Out
1. List the main threats to biodiversity worldwide.
Habitat destruction, pollution, global climate change, invasive species, and
overexploitation are the main threats.
2. Describe the relationships among the three levels of biodiversity. Why is each level
important?
High ecosystem diversity means more diverse habitats for different species, and therefore
increases species diversity. Within each species, genetic diversity increases the chance
that the species will survive in a changing environment.
3. In an article in Nature magazine, Sean Nee wrote: “Earth’s real biodiversity is
invisible, whether we like it or not.” What does that statement mean?
One interpretation is that bacteria and other microscopic organisms are extremely diverse,
although that diversity is difficult to measure. Moreover, these microbes ultimately
control the processes that support all life on Earth.
4. Which human activities promote habitat destruction?
Human activities that promote habitat destruction include deforestation, desertification,
alteration of river’s paths, pollution, and many other activities.
5. How can too much of a nutrient alter an aquatic ecosystem?
Nutrients and light fuel photosynthesis; excess nutrients promote the overgrowth of algae
and other autotrophs. As these autotrophs die, their bodies stimulate populations of
bacteria and other decomposers, whose respiration depletes the water of O2. Fish and
other organisms die.
6. How does the Gulf of Mexico’s “dead zone” demonstrate the connections among the
world’s ecosystems?
Farming practices from areas as far away as Minnesota cause a huge seasonal algal
bloom in the Gulf of Mexico. The resulting eutrophication causes such low oxygen levels
that aquatic life isn’t possible in the affected area.
7. Visit the waterfootprint.org website to see how much water is required to produce
various foods and beverages. Do you think it is important for an individual to choose
products with a low water footprint? Why or why not?
[Answers will vary]
8. How does the combustion of fossil fuels influence such different phenomena as acid
deposition and global climate change?
The combustion of fossil fuels releases sulfur and nitrogen oxides into the atmosphere,
where they join water and form sulfuric acid and nitric acid. These acids then return to
the Earth as acid deposition. At the same time, fossil fuel combustion also releases CO2,
a greenhouse gas that traps warmth near Earth’s surface.
9. Particulate air pollution damages animal respiratory tracts. How might dust-covered
leaves harm a plant?
Dust can block the sunlight that plants require in photosynthesis; dust may also block
stomata, pores that allow plants to acquire CO2 and exchange other gases with the
atmosphere. If the dust contains toxic components, it may kill plant cells outright.
10. In what ways is the greenhouse effect both beneficial and detrimental?
The greenhouse effect supports life, because Earth’s average temperature would be much
lower without its blanket of greenhouse gases. As CO2 accumulates in the atmosphere,
however, average global temperatures are rising. Changes in temperature or moisture can
alter populations, kill some organisms outright, stress others, or cause migrations.
Continued climate change will affect not only wild organisms but also agriculture and
public health.
11. Cite biological evidence of global climate change.
Biological evidence of global climate change includes a decrease in the amount of
permafrost, northward shifts in the ranges of butterflies, and changes in migration and
mating patterns of many species.
12. Explain the logic behind planting trees as a way to reduce global climate change.
Trees use CO2 in photosynthesis, incorporating much of it into long-lasting wood. They
can therefore temporarily help offset the release of CO2 into the atmosphere from the
burning of fossil fuels. Planting trees can also help offset the loss of trees from
deforestation.
13. Select a biome from chapter 38, and list three ways that an earlier spring and later fall
resulting from global climate change might affect biodiversity in that biome.
[Answers will vary; this is one example]. In the tundra, if the temperatures get warmer
earlier, decomposition will speed up, and soils may not be as rich in organic matter as
they usually are. The permafrost may start melting, which means plants may start to
grow too soon or establish larger root systems, which could throw off the balance of the
plants that have established a habitat in the frozen soil. Also, the migratory patterns and
mating rituals of birds and other animals could be disrupted.
14. Why are invasive species harmful?
Invasive species change the composition of a community. They also carry diseases that
spread to native species. Efforts to eradicate invasive species are expensive.
15. One approach to combat invasive species is to kill the invaders. In Hawaii, officials
shoot feral cats, goats, and pigs. In Australia, the government added chlorine and copper
to a bay to kill zebra mussels, killing everything living in the water. Do you think that
this is an effective approach? Suggest an alternative.
Killing all of the invaders is nearly impossible, and this “solution” may create new
environmental problems. An alternative way would be to increase populations of natural
predators or to reduce supplies of resources that the invaders require. Invasive species
are a persistent problem because there are no easy solutions.
16. Which of the strategies described in section 39.5 are being used in the Everglades
restoration project?
The project includes setting aside land and reversing habitat destruction.
17. Name three ways you can alter your lifestyle in a way that promotes conservation
practices.
Many answers are possible, but three ways you can alter your lifestyle are choosing foods
and products that reflect sustainable practices, encouraging manufacturers to change
packaging to reduce threats to wildlife, and paying attention to what you discard and pour
down the drain.
18. Search the Internet for information on the Convention on Biological Diversity and on
the international agreement called CITES. How does each approach tackle the
biodiversity crisis on a global scale?
The Convention on Biological Diversity covers all three levels of diversity and seeks not
only to conserve diversity but also to manage resources sustainably and to equitably share
genetic resources. CITES is an international trade agreement concerning endangered
species. This makes its focus largely at the species level of diversity.
19. Give an example of an environmental problem that can immediately reduce
biodiversity and one that has a delayed effect.
An environmental problem that can immediately reduce biodiversity is changing a river’s
path, which can cause stream bank erosion and choke out downstream communities. An
environmental problem that has a delayed effect is global climate change; CO2 released
into the air has caused the average global temperature to rise gradually.
20. Several polar bears were discovered that have reproductive organs of both sexes.
These bears also have high concentrations of PCBs in their blood, but researchers do not
know whether exposure to PCBs is related to the disturbed sexual development. Given
that many heavily polluted ecosystems are tainted with several types of pollutants, how
could you link exposure to one chemical to a specific biological effect?
To link exposure to one chemical to a specific biological effect, blood and fatty tissues
could be collected from bears with abnormal reproductive systems and bears with normal
reproductive organs. Soil and water samples could also be taken from the bears’ habitats.
If all of the samples were tested for potential pollutants, it might be possible to correlate
exposure to a pollutant with reproductive disturbances. Previous studies testing the effect
of organic pollutants on reproduction in other species could be helpful as well, along with
new experiments with laboratory animals that could reveal more about the mechanism of
disturbance.
21. In the southeastern United States, several species of freshwater mussels are extinct or
threatened because of habitat destruction. In the past, they were also harvested for the
button trade. How would a population ecologist (see chapter 36) approach the problem of
species recovery for these animals?
A population ecologist would consider the effects of migration, birth rates, and death
rates. One strategy would be to provide the habitat and other resources required to ensure
reproduction and survival; restricting harvesting and otherwise minimizing the death rate
would be helpful as well.
22. Your friend reads an article about scientists who are collecting DNA from endangered
species. She says, “I don’t know why we spend so much money to save these species
when we can just sequence their DNA.” Given what you know about the importance of
biodiversity, how would you respond?
Simply preserving the DNA does not preserve the role of the species in its ecosystem. In
addition, we cannot collect and preserve enough DNA samples to reflect the genetic
diversity of a species.
23. Use the Internet to search for examples of conflicts involving the Endangered Species
Act and the rights of private property owners. If you owned land that housed an
endangered species, what would you be willing to sacrifice to save the species? What
information would you need before answering this question?
[Answers will vary]
24. The red-cockaded woodpecker is an example of an “umbrella species” because
conserving this bird’s habitat will also protect many other species. Can you think of other
species in your area that might qualify as umbrella species?
Examples will vary by location but could include: northern spotted owl, California
gnatcatcher, white-backed woodpecker, Florida panther, and grizzly bear.
25. Use the Internet to learn about so-called “biodiversity hot spots.” Choose one to
investigate in detail. Why is the area you chose a hot spot? What are the main threats to
biodiversity in the area? What efforts are being made to preserve the area?
[Answers will vary]
26. Refer back to section 11.6, which describes the bottleneck effect. With this
information in mind, why might recovery be difficult for species, such as cheetahs, that
are nearly extinct?
With the great loss of genetic diversity that accompanies a bottleneck event, it is less
likely that a species will be able to respond to environmental changes, as there is little to
no variation for natural selection to work on.
Pull it Together
1. What are examples of pollutants in air and in water? Which of these pollutants
eventually reach land?
Many examples are possible; this is one correct answer. Pollutants in air include
particulates such as soot and methane gas from bovine herds. The soot gradually falls
back onto the land, but the methane remains in the atmosphere. Examples of water
pollutants include sewage. After water treatment, the solid waste remaining is often
spread onto land. Plastics can also be water pollutants that can wash ashore.
2. How does human population growth contribute to each of the main factors causing
species extinctions?
Habitat destruction, pollution, global climate change, invasive species, and
overexploitation are the main threats to biodiversity. As our population grows we use
more land, reducing available habitat. Additional pollution is another inevitable
consequence of population growth. We also continue to expand the intentional and
accidental global trafficking of other species, and in doing so we increase the introduction
of invasive species. People and industry demand energy, which currently comes from
fossil fuels; an expanding human population therefore means more CO2 emissions and
more climate change. Finally, a greater population means greater demand for all
resources, including overexploited species.
3. Give examples of government actions that threaten biodiversity and examples of
government actions that preserve biodiversity.
Many answers are possible, but here are some examples. Government actions that
threaten biodiversity include building roads in previously undeveloped areas, subsidizing
fossil fuel extraction and pollution-generating agricultural practices, and trading with
countries that have low pollution standards. Government actions that preserve
biodiversity include setting aside parks, subsidizing sustainable agriculture and clean
energy, setting taxes based on pollution generated, and educating citizens on how to
reduce, reuse and recycle their waste.