Chapter 9 Critical Thinking Questions
Mary Cleary, Justin Gagnon, Sam Cekada
1. A. Why do biotic factors that regulate population growth tend to
depend on population density?
Some factors that limit population growth have a greater effect as a population’s
density increases. Density dependent population controls include competition for
resources, predation, parasitism, and infectious disease.
B. Why do abiotic factors that regulate population tend to be
independent of population density?
These factors that regulate population are natural disasters and human caused.
Some examples include floods, hurricanes, habitat destruction, pesticide spraying and
pollution.
2. Why are pest species likely to be extreme r-selected species? Why are
many endangered species likely to be extreme K-selected species?
Because most pests tend to have high rate of population increase, have short life
spans, and reproduce early and often, causing exponential growth. Endangered species
are likely to be K selected because they do not reproduce as much and reproduce late in
life with small amount of offspring.
3. Why is an animal that devotes most of its energy to reproduction
likely to be small and weak?
R selected species devote most of their energy to reproduction because they generally
have short life spans so need to repopulate. This causes them to be small and weak
because they have short life spans and their goal is to reproduce many offspring
4. Given current environmental conditions, if you had a choice, would you
rather be an r-strategist or a K-strategist?
Given the current changing, unstable environmental conditions, I would rather
be an r-strategist than a K-strategist species. Since they produce such a large number of
offspring in such a small amount of time, although many of their offspring will not
survive in inclement climate, some will simply due to probability. K-strategists, on the
other hand, do not produce enough offspring quick enough to ensure survival of their
next generation if the few offspring they produce are killed by their environment.
5. List the type of survivorship curve you would expect given the
descriptions of the following organisms:
a. Early loss: As an annual plant, the organism has a consistent, short lifespan.
b. late loss: A mammal that doesn’t reach maturity until later in life. They also
protect their young offspring, lowering the number of young deaths.
6. Explain why a simplified ecosystem such as a cornfield usually is much
more vulnerable to harm from insects and plant diseases than a more
complex, natural ecosystem. Does this mean we should never convert a
grassland to a cornfield?
The simplification of an ecosystem drastically lowers levels of biodiversity, such
as a cornfield which only contains corn. If a disease or predator destroys the corn, the
ecosystem is destroyed, while if the same disease or predator were to enter a grassland,
they would only consume certain organisms, and would themselves be consumed by
other organisms. The simplified cornfield is no such food web, and so predators and
diseases can easily decimate the entirety of its corn. This does not mean that we should
never convert grasslands into cornfields, but it does mean that we should limit the
amount of land we develop, to avoid loss of ecosystems and their biodiversity, avoiding
dilemmas like the soil erosion that led to the dust bowl.
7. How has the human population generally been able to avoid
environmental resistance factors that affect other populations? Is this likely
to continue? Explain.
The human population has been able to avoid environmental resistance factors
that affect other populations because the human population is relatively adaptable, so it
is able to overcome factors such as too much or too little light or a too high or too low
temperature. Also, the human population can easily migrate, so they are able to remove
themselves from areas where there is an unfavorable chemical environment. This also
means that when a habitat is unsuitable or destroyed, they are able to move elsewhere,
as well. While humans do have a low reproductive rate individually, many populations
of humans have relatively high reproductive rates, producing more than the
reproductive rate of birth. Inadequate food supply is an issue for humans in developing
areas, but this is not the case in much of the world. The humans do not have any true
competitors for resources or any natural predators. While they are not especially
resistant to disease or parasites, they are able to produce vaccines, medicines, and
treatments to fight disease. Finally, humans live in basically every single climate area,
proving that they are able to withstand changes in climate and environment. This is
likely to continue into the foreseeable future, but it is not indefinitely sustainable. Many
of the reasons that make the human population able to overcome environmental
resistance reduce biodiversity and degrade the environment. If changes are not made to
the way that humans live, the environment will eventually be too degraded to support
humans.
8. Explain why you agree or disagree with the four principles of
sustainability listed in Figure 9-15 and their lessons for human societies
listed in Figure 9-15. Identify aspects of your lifestyle that follow or violate
each of these four sustainability principles. Would you be willing to change
aspects of your lifestyle that violate these sustainability principles? Explain.
The Principles of Sustainability are as follows: nature runs on renewable solar
energy; it recycles nutrients and wastes, leaving little waste in nature; it uses
biodiversity to maintain itself and adapt to new environmental conditions; and it
controls a species’ population size and resource use by interactions with its environment
and other species. I agree with all of these principles because they simply seem
unequivocal. We know that ecosystems run off of solar energy. We know that
ecosystems recycle nutrients and wastes. We know that biodiversity leads to better
adaptation to new conditions. We know that populations size is controlled by
environmental resistance. These principles do not seem to be able to be disagreed with
simply because they are fact.
The lessons from the Principles of Sustainability are as follows: humans should
rely mostly on renewable solar energy; we should prevent and reduce pollution and
recycle and reuse resources; we should preserve biodiversity by protecting ecosystem
services and preventing premature extinction of species; and we should reduce births
and wasteful resource use to prevent environmental overload and depletion and
degradation of resources. I violate the first one, that humans should rely on solar
energy, simply because I do not have the means to do so. Solar panels are very expensive
to purchase, making them an unattainable option. I would be willing to use them if I had
the means. I do participate in preventing pollution by reducing my own emissions from
my home and my car. I also participate in recycling and reusing of resources. I would
like to help to preserve biodiversity, but at the time I do not have much ability to do so. I
do not have enough knowledge of local endangered species or their habitats to truly
make a difference. Finally, I cannot say how I will affect the number of births, but I can
say that I plan to prevent wasteful resource use and environmental overload and
depletion and degradation of resources.