,Ecology, 9th edition by Sher and Molles
Answers to End-of-Chapter Review Questions
Chapter 1
1. The advantage of dividing the field of ecology into subdisciplines, each focusing on a single
level of organization is that such concentration and simplification tends to make the
hypotheses addressed more likely to be testable.
2. The pitfalls of subdividing nature is that important ecological relationships may go
unrecognized. Figure 1.1 misrepresents nature by converting the complexity of nature into an
abstract simplification and by picturing the natural world as a vertically nested hierarchy,
when in fact natural relationships and influences are more like a tangled web.
3. In the case of MacArthur’s warblers, you might compare the use of foraging zones by
warbler species in areas with the full complement of warbler species with the use of foraging
zones where one or more species is missing from the community. One way to test the role of
competition in excluding some American redstarts from productive feeding areas would be to
capture and remove the, presumably, dominant individuals from those areas to see if other
redstarts, especially females and young males would move in to replace the individuals
removed.
4. New technology allows us to see things we were not able to observe before, and ask
questions that we were not previously able to address. For example, drones can carry cameras
and other sensors to locations that are not easily accessible. Stable isotope analyses allow us
to trace water and nutrients through ecosystems. Genetic analyses allow us to identify gut
contents. Sound equipment allows us to hear things out of the range of human hearing.
Citizen science initiatives increase the number of eyes and ears collecting evidence.
Improved computing allows us to analyze larger data sets and run complex models to more
accurately predict future events.
5. The species composition of these forests has changed substantially and their composition is
likely to change in the future in response to climatic change.
6. There are trade-offs when comparing simple and complex models. While complex models
include more data/variables and potentially provide greater accuracy, they may also
incorporate more assumptions and therefore have a greater potential for error if any of those
assumptions are invalid.
Chapter 2
1. Use biome discussions as a guide.
2. Use figure 2.8 and the associated discussion as a guide.
3. Use figure 2.4 and associated discussion as a guide. High precipitation in the tropics is
produced by high rates of evaporation and subsequent condensation of water vapor in
ascending air masses. The clouds formed in this way produce the heavy precipitation
associated with the tropics. High precipitation at temperate latitudes is produced when warm
moisture bearing subtropical air meets cold polar air, which forces condensation of the water
vapor in the subtropical air mass. Many tropical environments experience drought during
periods of El Niño (see chapter 23).
4. The seasonal rainfall of these biomes is produced by shifts in the latitude at which the sun is
directly overhead. Figure 2.4a, which shows the sun directly overhead at the equator, which
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of
McGraw-Hill Education.
, generates storms through the processes of evaporation, condensation and precipitation of
water, is really a snapshot of a dynamic system. The latitude at which the sun is directly
overhead, which is sometimes called the "solar equator", and acting as a generator of tropical
storms shifts between 23.5° N and 23.5° S. The wet season comes during the warmer time of
the year when the sun is more nearly overhead. The dry season comes when the solar input is
less direct (sun's angle is more oblique).
5. Anywhere that the presence of mountains which can force precipitation in rising air masses
and form a "rain shadow" in the leeward (downwind) side. The height of mountains will
generally make a difference in the rain shadow effect, since higher mountains will induce
more precipitation in rising air masses.
6. One of the greatest differences is the presence of permanent snow and ice on mountains at
high latitudes.
7. One of the main differences between midlatitude and tropical alpine zones is that on tropical
mountains daily variation in temperature is nearly as great as seasonal variation. Tropical
alpine ecosystems lack fht every strong seasonality in input of solar radiation and
temperature that occurs in midlatitude alpine zones.
8. In tropical climates the dominant seasonal change is from wet season to dry season. At very
high latitudes it is cold much of the year with a brief cool growing season. In some tropical
countries, such as Costa Rica, people have divided the seasonal changes significantly than
has been done customarily in temperate climates. In the middle of the wet season, for
instance, there is a period of reduced rainfall which Costa Ricans call veranillo, which means
"little summer". The point here is that the seasonal terms associated with midlatitudes do not
fit the annual variations that occur in other parts of the earth. It would be interesting to
catalog the traditional terms for seasonal changes used by native peoples living in different
climatic zones.
9. There has been much greater connection and exchange across the tundra and boreal forests
which form nearly continuous bands in the northern hemisphere. In contrast, the temperate
woodland tropical rain forest biomes are highly fragmented with few opportunities for biotic
exchange over long periods of evolutionary history.
10. The most heavily impacted biomes have been temperate forest, temperate grassland, desert,
and temperate woodland. Areas of tropical dry forest have also been fairly heavily impacted.
Tropical rain forest, boreal forest, and tundra have received less impact. Satellite imagery
could be used to assess the density of human-induced change on landscapes. The very high
rates of human population growth in tropical countries and increasing resource extraction in
the northern biomes will likely increase human impact in these biomes.
Chapter 3
1. Use Figure 3.2 as a guide for your review. The major sources of freshwater are groundwater,
lakes, and rivers. A large amount of freshwater is also present as ice. Water shortages already
affect large regions of the world and groundwater levels are dropping in many regions. Even
where water remains plentiful, pollution is reducing water quality.
2. The proportion of the ecosystem receiving sufficient light to support photosynthesis is 200 m
divided by 4000 m, about 0.05 or 5% of the total.
3. Major challenges faced by organisms moving from an aquatic to a terrestrial environment
included lower support in the less dense aerial medium, greater temperature variation on
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of
McGraw-Hill Education.
, land, and desiccating water loss to air. Some advantages were less resistance to movement
through air, lower rate of heat loss to air, and higher oxygen concentrations.
4. Refer to figure 3.13 as you develop your answer. Darwin's developmental sequence was
tested by drilling on atolls, which revealed deep accumulations of ancient coral reefs
deposited on sunken volcanic mountains.
5. The main factor here is that, though urchins feed on young corals, they also suppress the
growth of algae, which reduces algal competition with the young corals. Thus the net effect
of urchins on coral establishment is positive.
6. The wide environmental fluctuations of the intertidal environment has probably selected for
greater physiological tolerance among intertidal species. Because of differences in the
intensity of selection, tolerance of variation in salinity should be higher in the upper intertidal
zone compared to the lower intertidal and subtidal zones.
7. Because small grain size reduces rates of water flow, oxygen concentration is generally lower
in the interstitial waters of fine sediments compared to coarse sediments. Oxygen
concentrations should be lower in tide pools in sheltered locations because of wave-related
circulation.
8. The most direct way to test these predictions would be to study the relative contributions of
litterfall from streamside forests and photosynthesis within the stream to the total energy
budget of the stream.
9. Two approaches have been used to study the influence of nutrient availability on lake
primary production. The first has involved measuring nutrient availability and rates of
primary production in a large number of lakes and looking for a correlation between these
two variables. The second approach has been to increase the nutrient availability in lakes and
measure primary production responses (see Chapter 18).
10. It is clear that that the introduction of exotic species has greatly altered the structure and
functioning of the Great Lakes ecosystem. However, the Great Lakes of Africa have also
been impacted by species’ introductions. See Chapter 17 online, which includes a discussion
of the effects of introducing Nile perch on the rich fish fauna of Lake Victoria.
Chapter 4
1. Darwin mainly conducted comparative studies of natural populations, while Mendel
conducted numerous experimental studies in his garden. In addition, Mendel used
mathematics extensively in his work, while Darwin did not. Darwin proposed potential
mechanisms for evolutionary change in species. Mendel discovered mechanisms of
inheritance. The studies of Darwin and Mendel prepared the way for the later studies
reviewed in this chapter by providing a mechanistic theory to explain evolution in organisms
and the genetic transmission of characteristics between generations.
2. Genetic variation within and between populations is required for evolutionary change. On the
surface, it is difficult to know if the phenotypic variation observed within and between
populations is due to genetic differences and local adaptation, or phenotypic plasticity
(identical genotypes producing different phenotypes when exposed to different
environmental conditions). Common garden experiments can be used to help distinguish
between these two sources of phenotypic variation. The observation of distinct differences
between individuals from the same source population grown in different environments
suggests phenotypic plasticity; while differences between individuals from different source
populations grown in the same environment supports true genetic variation and local
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of
McGraw-Hill Education.
Answers to End-of-Chapter Review Questions
Chapter 1
1. The advantage of dividing the field of ecology into subdisciplines, each focusing on a single
level of organization is that such concentration and simplification tends to make the
hypotheses addressed more likely to be testable.
2. The pitfalls of subdividing nature is that important ecological relationships may go
unrecognized. Figure 1.1 misrepresents nature by converting the complexity of nature into an
abstract simplification and by picturing the natural world as a vertically nested hierarchy,
when in fact natural relationships and influences are more like a tangled web.
3. In the case of MacArthur’s warblers, you might compare the use of foraging zones by
warbler species in areas with the full complement of warbler species with the use of foraging
zones where one or more species is missing from the community. One way to test the role of
competition in excluding some American redstarts from productive feeding areas would be to
capture and remove the, presumably, dominant individuals from those areas to see if other
redstarts, especially females and young males would move in to replace the individuals
removed.
4. New technology allows us to see things we were not able to observe before, and ask
questions that we were not previously able to address. For example, drones can carry cameras
and other sensors to locations that are not easily accessible. Stable isotope analyses allow us
to trace water and nutrients through ecosystems. Genetic analyses allow us to identify gut
contents. Sound equipment allows us to hear things out of the range of human hearing.
Citizen science initiatives increase the number of eyes and ears collecting evidence.
Improved computing allows us to analyze larger data sets and run complex models to more
accurately predict future events.
5. The species composition of these forests has changed substantially and their composition is
likely to change in the future in response to climatic change.
6. There are trade-offs when comparing simple and complex models. While complex models
include more data/variables and potentially provide greater accuracy, they may also
incorporate more assumptions and therefore have a greater potential for error if any of those
assumptions are invalid.
Chapter 2
1. Use biome discussions as a guide.
2. Use figure 2.8 and the associated discussion as a guide.
3. Use figure 2.4 and associated discussion as a guide. High precipitation in the tropics is
produced by high rates of evaporation and subsequent condensation of water vapor in
ascending air masses. The clouds formed in this way produce the heavy precipitation
associated with the tropics. High precipitation at temperate latitudes is produced when warm
moisture bearing subtropical air meets cold polar air, which forces condensation of the water
vapor in the subtropical air mass. Many tropical environments experience drought during
periods of El Niño (see chapter 23).
4. The seasonal rainfall of these biomes is produced by shifts in the latitude at which the sun is
directly overhead. Figure 2.4a, which shows the sun directly overhead at the equator, which
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of
McGraw-Hill Education.
, generates storms through the processes of evaporation, condensation and precipitation of
water, is really a snapshot of a dynamic system. The latitude at which the sun is directly
overhead, which is sometimes called the "solar equator", and acting as a generator of tropical
storms shifts between 23.5° N and 23.5° S. The wet season comes during the warmer time of
the year when the sun is more nearly overhead. The dry season comes when the solar input is
less direct (sun's angle is more oblique).
5. Anywhere that the presence of mountains which can force precipitation in rising air masses
and form a "rain shadow" in the leeward (downwind) side. The height of mountains will
generally make a difference in the rain shadow effect, since higher mountains will induce
more precipitation in rising air masses.
6. One of the greatest differences is the presence of permanent snow and ice on mountains at
high latitudes.
7. One of the main differences between midlatitude and tropical alpine zones is that on tropical
mountains daily variation in temperature is nearly as great as seasonal variation. Tropical
alpine ecosystems lack fht every strong seasonality in input of solar radiation and
temperature that occurs in midlatitude alpine zones.
8. In tropical climates the dominant seasonal change is from wet season to dry season. At very
high latitudes it is cold much of the year with a brief cool growing season. In some tropical
countries, such as Costa Rica, people have divided the seasonal changes significantly than
has been done customarily in temperate climates. In the middle of the wet season, for
instance, there is a period of reduced rainfall which Costa Ricans call veranillo, which means
"little summer". The point here is that the seasonal terms associated with midlatitudes do not
fit the annual variations that occur in other parts of the earth. It would be interesting to
catalog the traditional terms for seasonal changes used by native peoples living in different
climatic zones.
9. There has been much greater connection and exchange across the tundra and boreal forests
which form nearly continuous bands in the northern hemisphere. In contrast, the temperate
woodland tropical rain forest biomes are highly fragmented with few opportunities for biotic
exchange over long periods of evolutionary history.
10. The most heavily impacted biomes have been temperate forest, temperate grassland, desert,
and temperate woodland. Areas of tropical dry forest have also been fairly heavily impacted.
Tropical rain forest, boreal forest, and tundra have received less impact. Satellite imagery
could be used to assess the density of human-induced change on landscapes. The very high
rates of human population growth in tropical countries and increasing resource extraction in
the northern biomes will likely increase human impact in these biomes.
Chapter 3
1. Use Figure 3.2 as a guide for your review. The major sources of freshwater are groundwater,
lakes, and rivers. A large amount of freshwater is also present as ice. Water shortages already
affect large regions of the world and groundwater levels are dropping in many regions. Even
where water remains plentiful, pollution is reducing water quality.
2. The proportion of the ecosystem receiving sufficient light to support photosynthesis is 200 m
divided by 4000 m, about 0.05 or 5% of the total.
3. Major challenges faced by organisms moving from an aquatic to a terrestrial environment
included lower support in the less dense aerial medium, greater temperature variation on
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of
McGraw-Hill Education.
, land, and desiccating water loss to air. Some advantages were less resistance to movement
through air, lower rate of heat loss to air, and higher oxygen concentrations.
4. Refer to figure 3.13 as you develop your answer. Darwin's developmental sequence was
tested by drilling on atolls, which revealed deep accumulations of ancient coral reefs
deposited on sunken volcanic mountains.
5. The main factor here is that, though urchins feed on young corals, they also suppress the
growth of algae, which reduces algal competition with the young corals. Thus the net effect
of urchins on coral establishment is positive.
6. The wide environmental fluctuations of the intertidal environment has probably selected for
greater physiological tolerance among intertidal species. Because of differences in the
intensity of selection, tolerance of variation in salinity should be higher in the upper intertidal
zone compared to the lower intertidal and subtidal zones.
7. Because small grain size reduces rates of water flow, oxygen concentration is generally lower
in the interstitial waters of fine sediments compared to coarse sediments. Oxygen
concentrations should be lower in tide pools in sheltered locations because of wave-related
circulation.
8. The most direct way to test these predictions would be to study the relative contributions of
litterfall from streamside forests and photosynthesis within the stream to the total energy
budget of the stream.
9. Two approaches have been used to study the influence of nutrient availability on lake
primary production. The first has involved measuring nutrient availability and rates of
primary production in a large number of lakes and looking for a correlation between these
two variables. The second approach has been to increase the nutrient availability in lakes and
measure primary production responses (see Chapter 18).
10. It is clear that that the introduction of exotic species has greatly altered the structure and
functioning of the Great Lakes ecosystem. However, the Great Lakes of Africa have also
been impacted by species’ introductions. See Chapter 17 online, which includes a discussion
of the effects of introducing Nile perch on the rich fish fauna of Lake Victoria.
Chapter 4
1. Darwin mainly conducted comparative studies of natural populations, while Mendel
conducted numerous experimental studies in his garden. In addition, Mendel used
mathematics extensively in his work, while Darwin did not. Darwin proposed potential
mechanisms for evolutionary change in species. Mendel discovered mechanisms of
inheritance. The studies of Darwin and Mendel prepared the way for the later studies
reviewed in this chapter by providing a mechanistic theory to explain evolution in organisms
and the genetic transmission of characteristics between generations.
2. Genetic variation within and between populations is required for evolutionary change. On the
surface, it is difficult to know if the phenotypic variation observed within and between
populations is due to genetic differences and local adaptation, or phenotypic plasticity
(identical genotypes producing different phenotypes when exposed to different
environmental conditions). Common garden experiments can be used to help distinguish
between these two sources of phenotypic variation. The observation of distinct differences
between individuals from the same source population grown in different environments
suggests phenotypic plasticity; while differences between individuals from different source
populations grown in the same environment supports true genetic variation and local
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of
McGraw-Hill Education.
