Answers to Open-Ended Questions
Hoefnagels Essentials 2/e
Chapter 20
Answers to Mastering Concepts Questions
20.1
1. What is the value of diversity to humans and to ecosystems as a whole?
Humans directly rely on other species to provide food, shelter, energy, clothing, drugs,
and waste disposal. Ecosystems as a whole depend upon biodiversity to maintain food
webs (some of which include humans), participate in biogeochemical cycles, fix nitrogen,
produce oxygen, prevent flooding and soil erosion, and perform many other essential
“ecosystem services.”
2. Describe the relationships among the three levels of biodiversity. Why is each level
important?
The three levels of biodiversity are genetic diversity, species diversity, and ecosystem
diversity. Within a species, genetic diversity increases the chance of survival in a
changing environment. Species diversity means the number of different species; it is
important because each species contributes to ecosystem function in a unique way. High
ecosystem diversity means more diverse habitats for different species, and therefore
increases species diversity.
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 more distant future.
4. What is conservation biology?
Conservation biology is the study of biodiversity at all levels, with the goal of
understanding why species go extinct and preventing this outcome.
20.2
1. Which human activities account for most of the loss of terrestrial habitat?
Most habitat destruction occurs because of agriculture and urban growth.
2. How do dams and levees alter river ecosystems?
Dams flood some areas and deprive others of water, and they change the temperature,
oxygen content, and nutrient content of the water. Levees eliminate streamside habitat
and change the rate at which water flows. Confining a river to its channel also means that
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sediments and nutrients are flushed downstream rather than being deposited on
floodplains.
3. Why is damage to estuaries and coastlines especially devastating?
The young of many aquatic species develop in estuaries until they can move upstream to
rivers or into ocean waters. Damaging estuaries and other coastal habitats therefore kills
many organisms before they have a chance to reproduce.
20.3
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, particulates, and acid
deposition?
Major sources of industrial smog include power plants, factories, and households that
burn coal and oil. Photochemical smog comes from reactions of vehicle emissions in the
presence of sunlight in the atmosphere. Particulates include dust, soot, ash, pollen, and
other suspended particles. Coal-burning power plants are major sources of the sulfur and
nitrogen oxides that return to the land as acid deposition.
3. What effects do smog, particulates, the thinning ozone layer, and acid deposition have
on life?
Smog injures plants and causes human respiratory problems. Particulates may trigger
inflammation, shortness of breath, asthma, and cancer. The thinning ozone layer allows
UV radiation to reach Earth’s surface, causing an increase in skin cancer and cataracts.
UV radiation also may be partly responsible for die-offs of amphibians. Acid deposition
kills or weakens plants and disrupts food webs in acidified lakes.
20.4
1. Why is CO2 accumulating in Earth’s atmosphere?
Excess CO2 is accumulating from the burning of fossil fuels and from deforestation.
2. Describe how and why Earth’s climate has changed during the past century.
Earth’s average temperature has increased over the past century as the atmospheric
concentration of CO2 has climbed.
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3. 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.
20.5
1. What features characterize an invasive species?
An invasive species has been introduced to an area where it did not previously exist; it
also breeds in its new habitat and spreads widely from its point of introduction.
According to some definitions, a species must also damage the environment, human
health, or the economy to be considered invasive.
2. How do invasive species disrupt ecosystems?
Invasive species can consume other species, cause disease, and compete with native
species for sunlight, food, space, and other resources.
3. List examples of species declines caused by overexploitation.
Examples of species declines caused by overexploitation include the dodo, passenger
pigeon, Carolina parakeet, and commercially fished species such as tuna, flounder,
halibut, swordfish, and cod. Marine mammals, seabirds, sea turtles, and many other
species are not targets of commercial fishing but are nevertheless harmed by its practices.
20.6
1. What is the relationship between human population growth and conservation biology?
A growing human population destroys more and more native habitats and increases
pressures on natural resources in many ways. Biodiversity suffers. So, as population
growth continues, conservation biology becomes increasingly important in the attempt to
preserve biodiversity.
2. List and describe the tools that conservation biologists use to preserve biodiversity.
Conservation biologists can set aside protected habitat and reverse habitat destruction so
endangered species have a place to live. Laws and practices that protect endangered
species, regulate harvests, control nonnative predators, and develop ecotourism are useful
as well. Captive breeding and reintroduction help increase population numbers;
biotechnology may be useful for cloning extinct or endangered organisms or for
identifying undiluted gene pools in the wild.
3. How can scientists, governments, and ordinary citizens work together for
conservation?
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Scientists contribute new information about species declines or recovery, and government
policies can influence the actions of individuals and corporations. Ordinary citizens can
push for additional conservation efforts and take actions to reduce their personal impact
on the environment.
Write It Out
1. List the main threats to biodiversity worldwide.
The main threats are habitat destruction, pollution, global climate change, invasive
species, and overexploitation.
2. Explain why preserving biodiversity is important (or is not important) to you. Use the
Internet to explore ethical arguments about conservation.
[Answers will vary.]
3. Considering the many types of community and ecosystem interactions (see sections
19.4 and 19.6), explain why the loss of one species is likely to lead to declines in other
populations.
Organisms interact with one another in many ways. They live in or on one another, rely
on each other as a food source, or depend on each other to cycle chemicals through the
ecosystem. The web of interactions is extremely complex, so the loss of one species in an
ecosystem may impact many other populations.
4. As part of an effort to combat habitat loss, some conservationists suggest “assisted
migration,” in which scientists move endangered or threatened organisms to new habitats.
Discuss the possible advantages, disadvantages, and challenges of this strategy.
Assisted migration could be beneficial to species that are not able to disperse widely on
their own. Dispersal that occurs too slowly could lead to extinctions as the climate
changes. However, after colonizing a new area, the species could become invasive, which
would damage the local ecosystem. In addition, assisted migration is likely to be laborintensive and costly. Scientists also face the challenge of deciding when it is time to
move a species and in what habitat they should place it.
5. When trees are removed from an area, patches or strips of untouched trees often
intersperse the deforested land. How is the abiotic environment on the edge of these strips
or patches different from before the area was disturbed? What changes in vegetation
would you expect to see in the next few years? How might animals be affected by forest
fragmentation?
The trees on the edge have a lot more sun and wind exposure. The trees are less likely to
survive because understory plants, which now receive sunlight, can more effectively
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compete for resources. Animal populations that rely on intact trees will be divided when
the forest is fragmented. If they cannot easily move between fragments, deforestation will
lead to less interbreeding and lower diversity within each isolated group.
6. Nanoparticles are tiny bits of metal that are used in sunscreens, as a wastewater
treatment, and for many other purposes. Recent evidence suggests that nanoparticles are
toxic to phytoplankton, the primary producers at the base of many aquatic food chains.
Phytoplankton use the energy in sunlight to produce organic matter, and they consume
CO2 and release O2. Predict some possible consequences to biodiversity if nanoparticles
become a more common pollutant.
Reducing populations of phytoplankton could have ripple effects on aquatic ecosystems.
Since phytoplankton form the base of the aquatic food chain, the loss of these organisms
will mean less food for all other trophic levels as well. The loss of phytoplankton could
also amplify the effects of global climate change and reduce the amount of oxygen
available in the water column. Each of these consequences could mean the loss of species
as well.
7. How does the Gulf of Mexico’s “dead zone” demonstrate the connections among the
world’s ecosystems? How would you expect bird populations in the dead zone to be
affected?
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 cannot survive in the affected area. The dead zone indirectly harms bird
populations, especially those species that normally prey on organisms that cannot survive
in a low-oxygen environment.
8. Use the Internet to learn how pharmaceutical drugs end up in the water supply. What is
the proper way to dispose of pharmaceuticals in your area?
Pharmaceutical drugs end up in the water supply when people flush them down the toilet
or sink. Drugs thrown in the trash can leach out of landfills into the groundwater below,
which may lead back to the water supply. (Answers for the proper disposal of
pharmaceuticals in your area will vary.)
9. Use the Internet to research ways to make homes more energy-efficient. How does
reducing your monthly energy bill relate to the conservation of biodiversity?
Many actions can improve the energy efficiency of homes, such as using geothermal
heating, having proper insulation, and using low watt light bulbs. These energyconserving strategies do more than just lower your electric bill: Using less energy also
means that your local power plant produces less pollution and CO2, which means less
habitat destruction and less global climate change.
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10. 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 react with 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.
11. In what ways is the greenhouse effect both beneficial and harmful?
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.
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. DNA evidence recently confirmed the existence of a “pizzly bear,” the offspring of a
polar bear and a grizzly bear. Scientists hypothesize that some polar bears are staying on
the mainland because of the warming climate, so polar bears are encountering grizzlies
more often than in the past. Pizzly bears may be less fit than either polar bears or
grizzlies, so some people are advocating that they be killed. Make an argument for or
against this strategy. If human actions are contributing to the breeding behavior, do we
have an ethical obligation to intervene? Do you think polar bears have a better chance at
avoiding extinction if humans eliminate their hybrid offspring? Would evidence that
polar bears and grizzlies had interbred in the past change your answers?
Answers will vary. Some scientists claim that polar bears have a better chance at
surviving if hybrid offspring are killed, but this view may be advocating “pure” species
over hybrids. If polar bears were to go extinct, then eliminating pizzly bears would
eradicate the only remaining polar bear DNA. There is evidence that polar bears and
grizzlies have had periods of interbreeding in the past, so maybe these recent events are
not unusual.
14. One way to combat invasive species is to kill the invaders. In Hawaii, officials shoot
feral cats, goats, and pigs. In Australia, the government fought zebra mussels by adding
chlorine and copper to a bay, killing everything living in the water. Do you think that
these approaches are reasonable? Suggest alternative strategies.
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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.
15. List three ways you can alter your lifestyle to promote conservation.
Many answers are possible, but three ways you can alter your lifestyle are choosing foods
and other 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.
16. 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, which makes its focus largely at the species level of diversity.
17. Refer back to section 12.7, 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
variation for natural selection to work on.
18. Use the Internet to learn how aluminum is mined. How can recycling aluminum help
save rain forests?
Aluminum mining is an energetically expensive process. In rain forests, dams in the
rivers provide this energy. These dams also cause flooding and interrupt the movement of
wildlife. Recycling aluminum reduces the demand for aluminum mining, helping to
preserve rain forests.
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 cattle. The soot gradually falls back onto
the land, but the methane remains in the atmosphere. Examples of water pollutants
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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. Figure 20.18 has arrows connecting conservation strategies with threats to biodiversity.
For each arrow, list a specific way to implement the strategy. Also, add three new
connections to the figure; explain each one.
Habitat restoration reverses habitat destruction: Improve water delivery to wetlands in the
Florida everglades after canals and levees caused wetlands to dry up.
Habitat restoration removes invasive species: Send employees of the National Forest
Service to remove invasive species from protected areas.
Economic incentives pay for the removal of invasive species: Recruit crab fishers to hunt
invasive Chinese mitten crabs.
Economic incentives pay to prevent overexploitation: Provide government subsidies to
fishers who avoid overharvested predatory fishes.
Economic incentives reduce pollution and climate change: Provide tax credits for
purchasing fuel-efficient cars.
Limited harvests reduce overexploitation: Stop issuing hunting licenses for overharvested
species.
Biotechnology reverses overexploitation: Clone species that have become extinct, using
preserved DNA and a closely related species for egg donation.
Individual conservation efforts reduce pollution and climate change: Turn up the
thermostat in the summer and turn it down in the winter. This reduces energy use and
keeps the local power plant from having to work as hard.
Other connections are possible: Individual conservation efforts reduce overexploitation if
an individual refuses to buy from companies that use unsustainable fishing practices.
Individual conservation efforts may reduce habitat destruction if an individual writes to
local government officials about preserving native habitat. Individual conservation efforts
reduce invasive species if an individual only plants native species in the garden.
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.
4. Which tools save entire ecosystems? Which target individual species?
Captive breeding, biotechnology, reintroduction, and harvest regulation target individual
species while habitat restoration and individual conservation efforts might save
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ecosystems. Economic incentives might help individual species or entire ecosystems,
depending on the specific policy.
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McGraw-Hill Education.