Download Suggested Answers to End of Chapter 4

Suggested Answers to End of Chapter Questions
The following are examples of the material that should be contained in possible student answers to the end of chapter Critical
Thinking questions. They represent only a summary overview and serve to highlight the core concepts that are addressed in the text. It
should be anticipated that the students will provide more in-depth and detailed responses to the questions depending on an individual
instructor’s stated expectations.
1.
List three ways you could apply concept 4-4B in order to live a more environmentally sustainable lifestyle.
Answers may vary. Students may suggest that they would attempt to limit the effects of habitat fragmentation by planting native
vegetation in their yards in order to create or contribute to a habitat corridor. They could limit the extent to which their economic
activities support deforestation and habitat loss in foreign countries. They might also pursue political activity to oppose massive
habitat loss through the conversion of land into agriculture or suburban land uses.
2.
Explain what would happen to the ecosystem where American alligators live (Core Case Study) if the alligators went extinct.
Name a plant species and an animal species that would be seriously affected, and describe how each might respond to these
changes in their environmental conditions.
The ecosystem would be very much altered because the alligator acts as a keystone species. Native plants would suffer as trees
and shrubs took over the habitat. Many fish species and migratory birds would also suffer from the loss of alligators.
3.
What role does each of the following processes play in helping implement the four scientific principles of sustainability: (a)
natural selection, (b) speciation, and (c) extinction?
(a) Natural selection implements all four principles of sustainability. Solar energy produces the plants that provide the energy and
food for a great biodiversity of creatures living on the planet. Predator-prey relationships help to maintain the “survival of the
fittest” implications in natural selection and control population. The nutrients in the remains of the prey then get recycled back
through the system.
(b) Speciation impacts the biodiversity principle of sustainability. The more new species arise as a result of speciation, the greater
the biodiversity of the ecosystem. If the new species is a predator it could also impact the population control principle of
sustainability.
(c) Extinction results directly in a loss of biodiversity as the species is lost from the gene pool. The nutrients in the species will be
recycled through the ecosystem as the numbers decline until no more of the species are left. If the species that has become extinct
was a predator species, then it could also impact the population control principle of sustainability.
4.
Describe the major differences between the ecological niches of humans and cockroaches. Are these two species in competition?
If so, how do they manage to coexist?
Both cockroaches and humans are generalist species having very broad niches. This means that they can live in many different
places, eat a variety of foods, and tolerate a wide range of environmental conditions. Cockroaches have been around for 350
million years and have thrived throughout the evolutionary process. Humans are a recent addition to the planet. Cockroaches eat
almost anything and can live anywhere except in the polar regions. They can go for a month without food, survive for a month on
one drop of water, and can withstand high doses of radiation. Some cockroaches can even survive being frozen. These traits are in
contrast to humans. Additionally humans do not reproduce as fast as cockroaches, which have a very high reproductive rate.
Unlike humans, cockroaches also eat their own dead, and if food is scarce will even eat each other! Although cockroaches do live
in homes that are occupied by humans, they are not directly in competition with each other for resources. However, cockroaches
can evade been stepped on, as they have rapid response times, and the ability to see virtually in all directions at once.
Cockroaches carry bacteria and viruses that cause diseases in humans, and can cause allergic responses in susceptible individuals.
5.
How would you experimentally determine whether an organism is a keystone species?
A controlled experiment could be performed similar to the one conducted by Robert Paine on the rocky shoreline of the Pacific
coast of Washington State. He demonstrated the keystone role of the top-predator sea star Piaster orchaceus in an intertidal zone
community. Paine removed these mussel-eating sea stars from one rocky shoreline community but not from an adjacent
community, which served as the control group. Mussels took over and crowded out many other species in the community without
the Piaster sea stars. This type of experiment could be performed in other areas, with different species, to assess the role that
certain species have in an ecosystem and whether a species could be classified as a keystone species.
6.
Is the human species a keystone species? Explain. If humans were to become extinct, what are three species that might also
become extinct and three species whose population would probably grow?
Humans are likely a keystone species by virtue of their technology and the extreme manner in which they influence their habitat.
Were we to become extinct, their domesticates would most likely not survive. These would include pets, livestock, and crop
plants. Species whose populations would likely grow would be the ones human activities have had a detrimental effect on, such as
whales, mountain gorillas, and the many weeds we struggle to keep in check.
7.
How would you respond to someone who tells you: (a) that he or she does not believe in biological evolution by natural selection
because it is “just a theory,” and (b) that we should not worry about air pollution because natural selection will enable humans to
develop lungs that can detoxify pollutants?
(a) A theory is part of the process that scientists follow when investigating scientific evidence in order to explain their
observations. For a theory to be validated it has to be accepted by the scientific community and reviewed by the world’s leading
scientists. It has to stand up to scientific scrutiny. There is much fossil evidence to indicate that evolution through natural
selection has taken place. There are also some examples that evolution is in action today as evidenced by the color changes in
moths that has taken place since the industrial revolution. Indeed, evolution may just be a theory, but to date the theory has stood
the test of time within the scientific world. Until a better scientific explanation is put forward it will remain the explanation of
choice. Physicists and mathematicians give credence to the theory of relativity, because as yet no one has proven it wrong. Even
Einstein said that a thousand experiments can prove him right, but it would take only one experiment to prove him wrong. As yet,
that experiment has not been conducted so the theory of relativity, like the theory of evolution, remains the best scientific
explanation of our observations.
(b) Unfortunately, with the human species and other large species that do not reproduce large numbers of offspring rapidly,
natural selection will not take place quickly enough for our lungs to become resilient to air pollution. Maybe this adaptation could
take place over thousands or even millions of years, but in someone’s own lifespan this is not feasible. It is more feasible to tackle
the problem of air pollution and bring about its reduction, than it is to assume that humans will be able to adapt to these
undesirable environmental conditions in the short term.
8.
How would you respond to someone who says that because extinction is a natural process, we should not worry about the loss of
biodiversity?
It is true that as environmental conditions change some species may begin to disappear at a low rate. This is the background
extinction rate, and annually is around one to five species for every million species on the planet. However, scientists such as E.
O. Wilson suggest that human activities have increased the extinction rate to somewhere between 100 and 1000 times the natural
background rate. As more and more habitat is disturbed by human use and the resulting declines in biodiversity take place, we
could lose many species from the earth over a relatively small time scale. Tropical rain forests, coral reefs, and wetlands are some
of the most biodiverse areas on the earth, yet these are the regions that are under the most threat. Loss of biodiversity in these
regions will have a major effect on the ecosystems and bring about extinction rates that are well above the naturally occurring
background rates.
9.
Congratulations! You are in charge of the future evolution of life on the earth. What three things would you put on the top of your
list to do?
Student answers will vary but could include: increased conservation, preservation, and protection of habitat that allows for greater
biodiversity and ecosystem stability through continuing evolutionary processes; learn how to work and live within the four
principles of sustainability and apply these to the human ecosystem; and address some of the main anthropogenic causes of
environmental degradation and take measures to remedy these issues expediently to offset the negative effects that they may have
on the evolution of species-global warming, ozone thinning, etc.
10. List two questions that you would like to have answered as a result of reading this chapter.
Student answers will vary and provide a good starting point