Chapter 1, Ecology and How To Do It: Answers to Review Questions
Authored by Lee Kats and Gary Bucciarelli
1) Some temporal patterns in ecology need different lengths of time to be
detected because of the levels of life (physical scales and temporal scales)
that are investigated. Many different approaches are used to understand
ecological processes and these processes can occur at a variety of time scales
and at very different levels of life, from the molecular to the global level.
Given the differences between the life of a single-celled organism and
multicellular organisms, ecological investigations of these two different types
of organisms would require very different lengths of time to detect patterns.
2) Descriptive studies are valuable because they often serve as a starting point
for researchers. They act as a foundation to describe, understand, or explain
some phenomenon, pattern, or observation. However, if a study is only
descriptive it fails to explain what variables are important, and therefore
limits the explanatory power of ecological research. That is why experiments
are essential, because they aim to explain the processes responsible for such
observations or phenomenon. Experiments allow researchers to control the
variables under investigation and test how changes affect results. Descriptive
studies do not include controlled, experimental manipulations.
3) A natural field experiment is an experiment that is not planned. Instead,
researchers take advantage of a natural event that has occurred in the past,
such as historical fires, floods, or the retreat of a glacier, to evaluate how
ecological processes may be affected by such an event. As an example, refer
to the Cedar Creek studies, where abandoned agricultural lands were studied
to understand the process of succession. In this example, instead of forcing
people off of currently inhabited agricultural land and waiting decades for
succession to occur, the researchers used previously abandoned agricultural
land and historical data to understand the process of succession.
4) A search of the term ecology returns many definitions. An appropriate
definition should define ecology as a scientific study of species distributions
and abundances, that focuses on how interactions among organisms and
their environments determine distribution and abundance, and the
relationships between species and the transformation and flux of energy and
matter. This is an appropriate definition because it includes the multitude of
ways in that the field of ecology studies various hierarchical levels of life.
5) The Cedar Creek study aimed to understand patterns of succession by
looking at abandoned agricultural land at various stages. Had they only
looked at a single field and monitored it for 50 years they would have had no
, clear understanding of how the process of succession actually occurs. They
would have had data for one site over that time period, but nothing to
compare it with and no idea if the results were atypical or typical of the
succession process. The use of multiple sites allowed the researchers to look
at multiple successional stages and to compare data measured at all
localities. With this approach, the researchers were able to observe trends
across all sites and track the response of the environment through time. Any
variation between sites was not an issue because they could compare
responses at all sites to look for a trend, which they could not do with only
one site. Had they only had one site they would have had no statistical power
either (which is why we must include replicates, such as multiple sites, in the
experimental design!).
6) In the catchment studies, the inputs of acids, nutrients, and other materials
from the atmosphere were measured by the Hubbard Brooks scientists. They
found that large amounts of nitrogen inputs (ammonium and nitrate) were
being retained in their study forest. Clear-cutting resulted in a major loss of
dissolved substances and 40% more of the input precipitation being
exported. As plants begin to grow again in these forests, they will likely
uptake precipitation and dissolved substances. As a result, the amount of
precipitation and dissolved substances lost in the forest should decrease.
Through time their concentrations should begin to resemble levels measured
in the pre-cleared forest.
7) Whole-lake experiments, like the one performed in Canada using Lake 227,
were performed to test how one abiotic variable (phosphorous) affects the
stimulation of algal growth. Researchers were able to manipulate Lake 227
by dividing it in half with a plastic barrier and adding phosphorous to one
side. Lake 227 had the lowest levels of dissolved carbon dioxide in all lakes
studied, and the researchers knew that these very low levels of dissolved
carbon dioxide limited algal production. The controlled addition of
phosphorous to one side of the lake and the observed increase in algal
production in that half, provides very strong support for the hypothesis that
phosphorous greatly affects algal production without the need to replicate
the experiment in numerous lakes.
8) The introduction of brown trout led to changes in the production of algae due
to a reduction of invertebrate biomass. Laboratory experiments showed that
brown trout caused behavioral changes in macroinvertebrates (mayflies),
which feed on algae. Because of this disruption in feeding behavior, algal
biomass reached unusually high values in sites with brown trout.
9) Our confidence in the predictions of models can be limited because we use
them to explore situations where we actually do not have and maybe cannot
obtain actual data. Also, models cannot be expected to predict a perfect and
, complete description of the world. All models are limited to approximations,
and rely upon our current state of knowledge. Therefore, if the data we have
are not very reliable then the model likely will not make worthwhile
predictions.
Challenge Questions
1) Ecological evidence can be gained in many ways. Descriptive studies,
ecological models, and experimental studies can all be used to gather data
and test a question. There are many approaches that could be used to test a
question like “why are there more species in the tropics than at the poles?”
One approach could be to use models with historical environmental data to
test if more species evolved in the tropics due to habitat quality. Another
approach could be to estimate numbers of species between the north and
south poles and test if the number of species increases as you move closer to
the tropics.
2) There are many similarities in the forces driving species richness in an oral
community and a European grassland, which is why the science of ecology
can operate at multiple scales. We can expect that oral communities
experience environmental heterogeneity, competition, life and death,
disturbances, and predation just like species in a European grassland or any
other habitat for that matter. All living organisms are subject to such
ecological processes.
, Chapter 2, Ecology’s Evolutionary Backdrop: Answers to Review Questions:
Authored by Lee Kats and Gary Bucciarelli
1) Thomas Malthus was the author of An Essay on the Principle of Population
that was published in 1798. Malthus’ essay was focused on human
population growth. He presented the idea that human population growth was
constrained because of limited resources, disease, wars, and other disasters,
which slowed population growth. Thus, only a small proportion of humans
born, or who might have been born, actually survived. Darwin and Wallace
realized that this concept applied to all living organisms.
2) The philosopher Herbert Spencer described the process of natural
selection as “the survival of the fittest.” However, it is an unsatisfactory way
to describe natural selection because survival is only one aspect of natural
selection. Remember, differential reproduction is usually just as important.
Additionally, it is a phrase that does not make clear what the term “fittest”
refers to. Fitness is a term that commonly refers to individuals who survive
better, thus reproduce more and leave more descendants. Those individuals
will be more fit in some environments than others. But, in another
environment those individuals may not be as fit as individuals found in that
environment.
3) The essential difference between natural selection and the selection
practiced by breeders is that breeders select for a specific trait; they have an
aim. The process of natural selection has no goal. Breeders may select for a
specific trait that is favored by humans, like increased milk production in
cows. However, natural selection occurs because some individuals of a
species with a specific trait have survived and reproduced while others
lacking that trait have not.
4) A reciprocal transplant is an experimental method that tests how species
responds to each other’s environment. Translocating to a different and
similar habitat is essential. These experiments are useful in ecological studies
because they allow researchers to detect local specialization of an organism.
The reciprocal transplant of anemone species showed that individuals did
better in their own environment than in an alternative environment. They
were more likely to survive, more likely to be brooding juveniles of their
own, and they grew more (or at least shrunk less).
5) Sexual selection is a part of natural selection. In the guppy example,
females are acting as a selection pressure and predators as another. Overall,
there is differential reproductive success based on the number of spots males
have. Therefore, males with more spots are more fit (have higher numbers of
offspring) than males with fewer spots.
Authored by Lee Kats and Gary Bucciarelli
1) Some temporal patterns in ecology need different lengths of time to be
detected because of the levels of life (physical scales and temporal scales)
that are investigated. Many different approaches are used to understand
ecological processes and these processes can occur at a variety of time scales
and at very different levels of life, from the molecular to the global level.
Given the differences between the life of a single-celled organism and
multicellular organisms, ecological investigations of these two different types
of organisms would require very different lengths of time to detect patterns.
2) Descriptive studies are valuable because they often serve as a starting point
for researchers. They act as a foundation to describe, understand, or explain
some phenomenon, pattern, or observation. However, if a study is only
descriptive it fails to explain what variables are important, and therefore
limits the explanatory power of ecological research. That is why experiments
are essential, because they aim to explain the processes responsible for such
observations or phenomenon. Experiments allow researchers to control the
variables under investigation and test how changes affect results. Descriptive
studies do not include controlled, experimental manipulations.
3) A natural field experiment is an experiment that is not planned. Instead,
researchers take advantage of a natural event that has occurred in the past,
such as historical fires, floods, or the retreat of a glacier, to evaluate how
ecological processes may be affected by such an event. As an example, refer
to the Cedar Creek studies, where abandoned agricultural lands were studied
to understand the process of succession. In this example, instead of forcing
people off of currently inhabited agricultural land and waiting decades for
succession to occur, the researchers used previously abandoned agricultural
land and historical data to understand the process of succession.
4) A search of the term ecology returns many definitions. An appropriate
definition should define ecology as a scientific study of species distributions
and abundances, that focuses on how interactions among organisms and
their environments determine distribution and abundance, and the
relationships between species and the transformation and flux of energy and
matter. This is an appropriate definition because it includes the multitude of
ways in that the field of ecology studies various hierarchical levels of life.
5) The Cedar Creek study aimed to understand patterns of succession by
looking at abandoned agricultural land at various stages. Had they only
looked at a single field and monitored it for 50 years they would have had no
, clear understanding of how the process of succession actually occurs. They
would have had data for one site over that time period, but nothing to
compare it with and no idea if the results were atypical or typical of the
succession process. The use of multiple sites allowed the researchers to look
at multiple successional stages and to compare data measured at all
localities. With this approach, the researchers were able to observe trends
across all sites and track the response of the environment through time. Any
variation between sites was not an issue because they could compare
responses at all sites to look for a trend, which they could not do with only
one site. Had they only had one site they would have had no statistical power
either (which is why we must include replicates, such as multiple sites, in the
experimental design!).
6) In the catchment studies, the inputs of acids, nutrients, and other materials
from the atmosphere were measured by the Hubbard Brooks scientists. They
found that large amounts of nitrogen inputs (ammonium and nitrate) were
being retained in their study forest. Clear-cutting resulted in a major loss of
dissolved substances and 40% more of the input precipitation being
exported. As plants begin to grow again in these forests, they will likely
uptake precipitation and dissolved substances. As a result, the amount of
precipitation and dissolved substances lost in the forest should decrease.
Through time their concentrations should begin to resemble levels measured
in the pre-cleared forest.
7) Whole-lake experiments, like the one performed in Canada using Lake 227,
were performed to test how one abiotic variable (phosphorous) affects the
stimulation of algal growth. Researchers were able to manipulate Lake 227
by dividing it in half with a plastic barrier and adding phosphorous to one
side. Lake 227 had the lowest levels of dissolved carbon dioxide in all lakes
studied, and the researchers knew that these very low levels of dissolved
carbon dioxide limited algal production. The controlled addition of
phosphorous to one side of the lake and the observed increase in algal
production in that half, provides very strong support for the hypothesis that
phosphorous greatly affects algal production without the need to replicate
the experiment in numerous lakes.
8) The introduction of brown trout led to changes in the production of algae due
to a reduction of invertebrate biomass. Laboratory experiments showed that
brown trout caused behavioral changes in macroinvertebrates (mayflies),
which feed on algae. Because of this disruption in feeding behavior, algal
biomass reached unusually high values in sites with brown trout.
9) Our confidence in the predictions of models can be limited because we use
them to explore situations where we actually do not have and maybe cannot
obtain actual data. Also, models cannot be expected to predict a perfect and
, complete description of the world. All models are limited to approximations,
and rely upon our current state of knowledge. Therefore, if the data we have
are not very reliable then the model likely will not make worthwhile
predictions.
Challenge Questions
1) Ecological evidence can be gained in many ways. Descriptive studies,
ecological models, and experimental studies can all be used to gather data
and test a question. There are many approaches that could be used to test a
question like “why are there more species in the tropics than at the poles?”
One approach could be to use models with historical environmental data to
test if more species evolved in the tropics due to habitat quality. Another
approach could be to estimate numbers of species between the north and
south poles and test if the number of species increases as you move closer to
the tropics.
2) There are many similarities in the forces driving species richness in an oral
community and a European grassland, which is why the science of ecology
can operate at multiple scales. We can expect that oral communities
experience environmental heterogeneity, competition, life and death,
disturbances, and predation just like species in a European grassland or any
other habitat for that matter. All living organisms are subject to such
ecological processes.
, Chapter 2, Ecology’s Evolutionary Backdrop: Answers to Review Questions:
Authored by Lee Kats and Gary Bucciarelli
1) Thomas Malthus was the author of An Essay on the Principle of Population
that was published in 1798. Malthus’ essay was focused on human
population growth. He presented the idea that human population growth was
constrained because of limited resources, disease, wars, and other disasters,
which slowed population growth. Thus, only a small proportion of humans
born, or who might have been born, actually survived. Darwin and Wallace
realized that this concept applied to all living organisms.
2) The philosopher Herbert Spencer described the process of natural
selection as “the survival of the fittest.” However, it is an unsatisfactory way
to describe natural selection because survival is only one aspect of natural
selection. Remember, differential reproduction is usually just as important.
Additionally, it is a phrase that does not make clear what the term “fittest”
refers to. Fitness is a term that commonly refers to individuals who survive
better, thus reproduce more and leave more descendants. Those individuals
will be more fit in some environments than others. But, in another
environment those individuals may not be as fit as individuals found in that
environment.
3) The essential difference between natural selection and the selection
practiced by breeders is that breeders select for a specific trait; they have an
aim. The process of natural selection has no goal. Breeders may select for a
specific trait that is favored by humans, like increased milk production in
cows. However, natural selection occurs because some individuals of a
species with a specific trait have survived and reproduced while others
lacking that trait have not.
4) A reciprocal transplant is an experimental method that tests how species
responds to each other’s environment. Translocating to a different and
similar habitat is essential. These experiments are useful in ecological studies
because they allow researchers to detect local specialization of an organism.
The reciprocal transplant of anemone species showed that individuals did
better in their own environment than in an alternative environment. They
were more likely to survive, more likely to be brooding juveniles of their
own, and they grew more (or at least shrunk less).
5) Sexual selection is a part of natural selection. In the guppy example,
females are acting as a selection pressure and predators as another. Overall,
there is differential reproductive success based on the number of spots males
have. Therefore, males with more spots are more fit (have higher numbers of
offspring) than males with fewer spots.
