study guides

1. CHAPTER 14 “TAKE-HOME MESSAGE” CHALLENGE QUESTIONS
14.1 Describe the terms individual, population, community, and ecosystem as they
related to one another. Define population density.
Answer: A single organism is an individual. An interbreeding group of these organisms
is a population. Populations of different species that interact with each other in a
particular area are a community. This community, together with the non-living elements
of the area, form an ecosystem.
14.2 How do the main units of focus in biology and ecology differ?
Answer: Much of biology focuses on the individual. Ecology, however, focuses on
organisms at the level of the population.
14.3 How many of the five million eggs that a cod lays during its lifetime are likely to
survive to reproduce? How many of an elephant’s babies are likely to survive to
reproduce?
Answer: In both cases, only an average of two offspring will survive to reproduce,
replacing their parents.
14.4 Population “A” is subject to heavy density-dependent factors, such as reduced
food supplies, but not a lot of density-independent factors, such as earthquakes, while
population “B” is repeatedly affected by density-independent factors but not many
density-dependent factors. Which of these two populations is more likely to be
experiencing exponential growth? Why?
Answer: Population “B.” Population “B” is in an environment in which “bad luck”
events such as earthquakes, fires, and floods occur repeatedly. As a result, this population
might never have time to grow as high as the carrying capacity and might perpetually be
in exponential growth.
14.5 Is it a problem for science, biology, and ecology that there are well documented
exceptions to the logistic growth pattern model (s-shaped curve)?
Answer: No. Nature isn’t always tidy, but there are practical reasons for finding the best
possible answers in science. If you are taking a lab with this course, you have probably
already gotten some results that were far from what you predicted. Such occurrences are
an important part of experiencing science.
14.6 What is meant by maximum sustainable yield?
Answer: The maximum sustainable yield is a special case in which as many individuals
as possible are removed from the population without impairing its growth rate. This
generally involves reducing the population size to half of the environment’s carrying
capacity.
14.7 How is an organism’s litter size shaped by natural selection?
Answer: As the term “reproductive investment” implies, there are costs and risks to an
organism in producing offspring. The number of offspring an organism produces in a
single litter can only go so high without taking such a toll that the individual is unlikely

2. to live to have another litter. Thus, for many organisms, a smaller litter size—allowing
the individual to have more litters in the future—is favored by natural selection.
14.8 How is a survivorship curve for a giant tortoise different from that of a mackerel?
Answer: A giant tortoise has high survivorship throughout most of its life, which rapidly
decreases late in life. The mackerel has high mortality early in life, but those that survive
the early years live long lives. These survivorship curves are type I and type III,
respectively.
What is the survivorship curve of humans?
Know what the three types of survivorship curves are, and what would be a
representative animal from each.
14.9 Explain why the litter sizes of mammals living closer to the equator might be
smaller than those in higher latitudes? How are these smaller litter sizes offset?
Answer: Areas closer to the equator do not have severe winters and, thus, the breeding
seasons are long enough to allow mammals multiple reproductive episodes per year. An
offsetting evolutionary factor is that these reproductive episodes tend to produce fewer
offspring.
14.10 Does natural selection act upon a mutation that causes death at age fifty? Explain.
Answer: No. Since very little reproduction occurs after the age of fifty, death at this
time would come after reproduction had already occurred, and the mutation would
already have been passed on.
14.11 A hazard factor is a measure of the risk of death for individuals in the population
from all types of external forces. A high hazard factor will favor individuals that
reproduce early, and will not be effective in weeding out alleles causing premature death.
How does a low hazard factor influence longevity?
Answer: A low hazard factor will lead to later reproduction and will weed out alleles
causing premature death except those having their effects very late in life.
14.12 Is it possible to produce, through artificial selection, fruit flies that live twice as
long as normal? Explain.
Answer: Yes. If one simply collects eggs laid by the longest-lived flies from each
generation, the average lifespan will be dramatically increased fairly quickly.
14.13 The age pyramid for the United States shows a baby boomer “bulge” resulting
from the unusually large number of babies born from the late 1940s to the early 1960s,
who are now reaching retirement age. There is concern that the current number of
working individuals is not great enough to sufficiently contribute to cover the retirement
system payouts promised to the baby boomers. Why wouldn’t another “baby boom”
solve this problem?
Answer: This problem is immediate and individuals born today will take many years to
reach the workforce. In the meantime, they also require resources for support.
14.14 What areas of the world have not yet completed their demographic transitions and
still display dangerously fast rates of population growth?

3. Answer: Mexico, Brazil, Southeast Asia, and most of Africa have not yet completed
their demographic transitions, and display fast rates of population growth.
14.15 For all of the considerable success of the human species, ultimately human
population growth will face limits. Why?
Answer: Like every other species, human environment has a carrying capacity beyond
which the population cannot be maintained.
Population oscillation – like the example we did in class with the snowshoe hare and
lynx.
Life histories – what they are based on
Gestation – mammals, shortest and longest
Current human population – 7.1 billion people on Earth
CHAPTER 15 “TAKE-HOME MESSAGE” CHALLENGE
QUESTIONS
15.1 An ecosystem is made of two components: the biotic environment, or community,
consisting of the living organisms within an area, and the physical environment, or the
habitat in which these organisms live. A habitat consists of its chemical resources of the
soil, water, and air as well as its physical conditions. List some of the aspects that make
up the physical conditions of a habitat. Abiotic
Answer: Temperature, salinity, moisture, humidity, and energy sources.
15.2 Terrestrial biomes are determined by the temperature and precipitation amounts as
well as whether those factors are constant or vary by season. By contrast, how are aquatic
biomes determined?
Explain climate.
Answer: Aquatic biomes are defined by physical features such salinity, water
movement, and depth.
15.3 Global weather patterns are mainly determined by the amount of solar energy
falling on an area. The amount of solar energy that falls on an area largely depends on the
angle at which this light hits the earth. Explain what this means. Explain where deserts
are located.
Answer: Because the earth is round, solar energy hitting at a Pole is spread out over a
wider area compared to an equal amount of solar energy hitting the earth at the equator.
15.4 A rain shadow is a dry region on the landward side of a mountain range. How is
it formed?
Answer: As moist air blows against this mountain, it rises, cools, and loses its moisture
as precipitation. As this drier air passes across the mountain range, it warms and does not
lose its moisture as precipitation, and perhaps even pulls moisture from the soil.

4. 15.5 Why is most of Europe significantly warmer than regions in Canada at the same
latitude?
Answer: The Gulf Stream brings warm water from near the equator to this area,
warming it significantly.
15.6 What is the difference between a food chain and a food web?
Answer: A food chain indicates the trophic level to which each organism belongs:
primary producers, primary consumers, secondary consumers, or tertiary consumers. A
food web acknowledges that many organisms operate at multiple trophic levels. For
example, a human eating a hamburger is both a primary consumer and a secondary
consumer.
15.7 Only about 10% of the biomass of an organism at one trophic level is converted
into biomass of an organism at the next trophic level. List a consequence of this
inefficiency.
What is biomass?
What is the 10% rule?
Where is most of the world’s carbon stored?
Answer: 1) There are far more plants than animals. 2) The top carnivores are relatively
rare.
15.8 How is the ocean to a thirsty shipwreck victim like nitrogen gas in the atmosphere
to most organisms?
Answer: Both are abundant and both are unusable. More than 78% of the atmosphere is
nitrogen gas, but for most organisms nitrogen is only usable after its bonds are broken
down in the soil by nitrogen-fixing bacteria.
15.9 What is coevolution?
Answer: Coevolution is a situation in which the evolution of one species significantly
affects the evolution of a second species, which in turn again affects the evolution of the
first species, and so on.
15.10 What factors are encompassed by an organism’s niche?
Answer: An organism’s niche encompasses the space it requires, the type and amount of
food it consumes, the timing of its reproduction, its temperature and moisture
requirements, and virtually every other aspect that describes the way the organism uses
its environment.
15.11 Use the sporting competition terms of “win,” “lose,” and “tie” along with
biological terms from this section to describe possible outcomes when two related species
have completely overlapping niches?
Answer: With competitive exclusion, one species will win while the other species will
lose by being driven to extinction in that location. In resource partitioning, the two
species can tie by altering their use of the niche, dividing the resources.
15.12 Behavioral adaptations exhibited by organisms in order to reduce predation

5. include hiding or escaping (as exhibited by many long-legged mammals), and alarm
calling and fighting back (as exhibited by Belding’s ground squirrels). List two physical
adaptations exhibited by organisms in order to reduce predation.
Answer: Physical adaptations exhibited by prey include mechanical defenses such as the
quills of a porcupine, chemical defenses such as the toxic strychnine produced by certain
plants, warning coloration such as that found on monarch butterflies, and camouflage
such as that found in many leaf- or twig-resembling insects.
15.14 Mutualism is a symbiotic relationship between two species in which both
organisms benefit. Describe two examples.
Answer: Succession does lead to climax communities, but only in the absence of
disturbance. However, disturbance is a fundamental part of most ecosystems.
15.16 In architecture, a keystone is the large stone at the top of an arch, which keeps the
two sides of the arch in place. How is a keystone species like a keystone in an arch?
Answer: Both the keystone and the keystone species have a large influence on the
composition of their “structures” (the arch and the community respectively). A keystone
literally holds together an arch. The presence of the keystone species keeps together
species diversity in a community.
CHAPTER 16 “TAKE-HOME MESSAGE” CHALLENGE QUESTIONS
16.1 Biodiversity offers a great deal of medical and economic value, but also offers
non-utilitarian values including aesthetic, symbolic, and naturalistic. What is the
fundamental difference between the two types of value?
Answer: The utilitarian values of biodiversity are quantifiable, and in some ways, far
easier to explain than the considerable non-utilitarian values of biodiversity. This is
especially the case when a discussion of biodiversity is based on an economic issue.
16.2 Biodiversity is most commonly defined as the number of distinct species in a
habitat, though sometimes this is slightly modified to include the number of different
classes or families of organisms. At what levels can biodiversity be considered?
Answer: Biodiversity can be considered at multiple levels, from the ecosystem to
species to genes and alleles.
16.3 Twenty-five diversity hotspots are home to 20% of the world’s species. What
three types of habitats are highly represented among these hotspots? About how much of
the world’s surface do these hotspots cover and where do they tend to be found on the
globe?
Answer: Tropical rain forests, coral reefs, and islands are areas of significant
biodiversity where this biodiversity is at high risk. The 25 hotspots cover only 1% of the
world’s surface and tend to be found in areas nearer to the equator than farther away.
Why is Madagascar important?
16.4 Describe the two fundamental components of MacArthur and Wilson’s theory of
island biogeography. What was the function of this theory?

6. Answer: MacArthur and Wilson stated that there is a close relationship between the
number of species inhabiting the island and the island’s area, and that the farther an
island is from the mainland, the fewer species it held. This theory was designed to
explain and predict the patterns of species diversity on islands.
16.5 Describe a hypothetical species that would be at the highest risk of background
extinction in terms of the factors of geographic range, population size, and habitat
tolerance.
Answer: The unfortunate species would have a restricted geographic range, a small
population, and a narrow habitat tolerance.
16.6 Biologists believe we are in the midst of a mass extinction. How is this supported
in terms of historical background extinction rates and the current extinction rates?
Answer: Historical background extinction rates are about one extinction per million
species per year. Current extinction rates are 1,000 times greater or more than this.
16.7 Describe the conditions under which an ecosystem disturbance is reversible.
Answer: Ecosystem disturbances are only reversible when the alteration of the habitat
does not include the complete extinction of any species.
16.8 Use the introduction of the brown tree snake onto the island a Guam in a brief
illustration of the two key characteristics that make an invasive species particularly
harmful?
Answer: Guam has no native snakes, and thus, there were no predators to the brown tree
snake in its new habitat—causing their populations to grow unchecked. Because the
native species of birds on Guam had never encountered snakes, they had no mechanisms
to compete with or defend themselves against the snakes. As a result, brown tree snakes
have eradicated most of the native species of birds on Guam.
16.9 What is the key factor that makes acid rain and acid fog more than just a local
phenomenon?
Answer: Wind currents can carry sulfur dioxide and nitrogen dioxide far beyond the
points of their origin.
16.10 Is global warming real, and is it caused by human activities?
Answer: Yes to both. There is no longer any question that human activities contribute
to global warming. The real questions we have to address today concern what the effects
of global warming will be, and what we need to do to stop it.
16.11 Science created the chlorofluorocarbons (CFCs), which have damaged the ozone.
But how does the reduction of CFC production, the stabilization of the atmospheric levels
of ozone, and the potential for full recovery of the ozone by 2065 represent a “success”
for science?
Answer: When CFCs were first introduced, they were considered harmless. Science
identified CFCs as the cause of ozone depletion and helped convince countries of the
world to adopt policies to discontinue the use of CFCs.
16.12 List some of the challenges that must be faced in addressing the problem of

7. tropical deforestation.
Answer: 1) The most diverse areas must be identified and protected, 2) the poverty that
necessitates the destruction must be dealt with, 3) alternative sources of food and income
must be developed, 4) population growth must be reduced, and 5) education about the
value of preserving biodiversity must be increased.
16.13 Have the effects of the Endangered Species Act been uniformly good?
Answer: No. Though approximately forty species once listed as endangered – including
the bald eagle, the peregrine falcon, the gray whale, and the grizzly bear – have made
remarkable recoveries and have been taken off the list, there have been unintended
adverse outcomes as well. An effect of the ESA is to focus most conservation efforts on
the preservation of individual species and populations, sometimes at the expense of other
elements of biodiversity and sometimes at the expense of efforts to reduce the loss of
ecologically important habitats.
16.14 The preservation of particularly distinctive and charismatic flagship species, such
as the panda or mountain gorilla, can engender significant public support, and preserving
their habitats can serve to preserve many other species as well. Describe one of the other
three strategies targeting individual species for conservation that has been particularly
successful at preserving large amounts of biodiversity beyond that single species.
Answer: 1) Preservation of keystone species is particularly important, since their loss
can lead to massive changes in the composition of species in an ecosystem. 2)
Preservation of indicator species, whose presence is an indicator of air or water quality,
helps to preserve conditions that make an ecosystem healthy. 3) The preservation of
wide-ranging umbrella species with large needs for habitat and other resources results in
the protection of numerous other species within the same habitat.
Habitat loss