Mastering Concepts
40.1
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 diversity at all levels, with the goal of understanding
why species go extinct and preventing this outcome.
40.2
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
sediments and nutrients are flushed downstream rather than being deposited on
floodplains.
3. Why is damage to estuaries especially devastating?
The juveniles of many aquatic species develop in estuaries until they can move upstream
to rivers or into ocean waters. Damaging estuaries therefore kills many organisms before
they have a chance to reproduce.
40.3
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 acid
deposition.
3. What effects do smog, particulates, acid deposition, and the thinning ozone layer have
on life?
Smog injures plants and causes human respiratory problems. Particulates block
photosynthesis; in humans, they may also trigger inflammation, shortness of breath,
asthma, and cancer. Acid deposition disrupts food webs in acidified lakes, kills forest
trees, and may play a role in die-offs of amphibians. The thinning ozone layer allows 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.
40.4
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 changed during the past century.
Earth’s climate has changed as the atmospheric concentration of CO2 and average global
temperatures have increased.
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.
40.5
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 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.
40.6
1. What is the relationship between human population growth and conservation biology?
As the human population grows, we destroy habitats and increase 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 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?
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.
40.7
1. Explain why subpopulations of alpine chipmunks have more genetic differences now
than they did a century ago.
Modern populations of alpine chipmunks are geographically isolated. With no
interbreeding between populations, each group is evolving independently.
2. How might the isolation of modern alpine chipmunk subpopulations have led to
reduced genetic diversity in the species?
As alpine chipmunks move to higher elevations, the species undergoes population
bottlenecks (see section 12.7). Each isolated population has a subset of the species’
genetic diversity. As some populations die, the overall genetic diversity of the species
decreases.
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. 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. People and industry demand energy, which currently
comes from fossil fuels; an expanding human population therefore means more CO2
emissions and more climate change. 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. Finally, a growing population means greater demand for all
resources, including overexploited species.
3. 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
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.
4. 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.
5. 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 cannot survive in the affected area.
6. How does the combustion of fossil fuels influence 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.
7. When standardized for energy production, burning coal produces more CO2 than any
other fossil fuel. Some United States politicians advocate “clean coal.” Use the Internet to
research and explain methods of reducing CO2 emissions from burning coal.
Answers will vary. Strategies for reducing CO2 emissions from burning coal include
“carbon capture and storage.” In this process, CO2 “sponges” (tiny crystals that bind to
CO2) capture the emissions, which are subsequently pumped into the ground.
8. 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 doesn’t have to work as hard. It produces less pollution
and CO2, which means less habitat destruction and less global climate change.
9. 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.
10. 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.
11. 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.
12. Explain how the threats to biodiversity summarized in the acronym HIPPO contribute
to climate change.
HIPPO stands for habitat destruction, invasive species, population, pollution, and
overexploitation. Deforestation (a form of habitat destruction and a form of
overexploitation) removes primary producers from the global ecosystem. Trees capture
CO2 from the atmosphere. An increasing population has increasing energy demands.
More power plants are built to meet these demands, contributing to a rise in CO2
emissions and other forms of pollution. More humans also mean more vehicles, which
add to greenhouse gas emissions.
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
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 do 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. Select a biome from chapter 39, 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, so 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.
15. 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.
16. One approach 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.
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.
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. 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.
19. 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 37) 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.
20. 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]
21. 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.
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
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. Use arrows to connect each threat to biodiversity listed in figure 40.27 to one or more
conservation strategies that might remedy the threat. If a threat to biodiversity does not
connect to any of the listed conservation strategies, then explain how we might address
the threat. Explain conservation strategies that do not connect to biodiversity threats
listed in the figure.
Habitat preservation and reversing habitat destruction helps to remedy habitat loss.
Predator control helps reduce the impact of some invasive species. Limited harvests and
economic incentives reduce the threat of overexploitation. Legislative action can help
control pollution. Captive breeding and biotechnology help to sustain populations that are
near extinction.
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.