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Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 58
Test Yourself Questions
1. The number of species in a community is called
a. species complexity.
b. community complexity.
c. species richness.
d. species diversity.
e. species abundance.
Answer: c. Species richness is the number of species in a community, but does not take into
consideration the relative abundance of each species.
2. Which of the following statements best represents the productivity hypothesis regarding species
richness?
a. The larger the area, the greater the number of species that will be found there.
b. Temperate regions have a lower species richness due to the lack of time available for
migration after the last ice age.
c. The number of species in a particular community is directly related to the amount of plant
biomass available for consumers.
d. As invertebrate productivity increases, species richness will increase.
e. Species richness is not related to primary productivity.
Answer: c. The productivity hypothesis suggests a direct relationship between productivity, measured by
the amount of plant biomass, and species richness.
3. The Shannon diversity index is a measure of
a. the number of different species in a community.
b. the abundance of a species in a community.
c. the types of species found in a typical climate.
d. the number of different species and their relative abundance in a community.
e. the distribution of members of a species in a community.
Answer: d. The Shannon diversity index allows ecologists to quantify both the number of species and
their relative abundance in a community.
4. Metagenomics is a field of study that
a. determines the similarities of the genomes of all species in a community.
b. focuses on the microbial genomes contained in a community.
c. compares the genomes of similar species in different communities.
d. none of the above.
e. both a and b.
Answer: b. Metagenomics allows researchers to characterize the microbial members of a community by
identifying and analyzing the microbial genomes in the community.
5. Extreme fluctuations in species abundance
a. lead to more diverse communities.
b. are usually seen in early stages of community development.
c. may increase the likelihood of extinction.
d. have very little effect on species richness.
e. are characteristic of stable communities.
Answer: c. Drastic changes in the number of individuals in a population are of concern because of the
likelihood of extinction.
6. Which of the following statements best represents the relationship between species diversity and
community disturbance?
a. Species diversity and community stability have no relationship.
b. Communities with high levels of disturbance are more diverse.
c. Communities with low levels of disturbance are more diverse.
d. Communities with intermediate levels of disturbance are more diverse.
e. Communities with intermediate levels of disturbance are less diverse.
Answer: d. Research seems to indicate that the most diverse communities seem to have intermediate
levels of disturbance.
7. The process of primary succession occurs
a. around a recently erupted volcano.
b. on a newly plowed field.
c. on a hillside that has suffered a mudslide.
d. on a recently flooded riverbank.
e. none of the above.
Answer: a. Primary succession occurs in an area that is newly exposed and was not previously
occupied by soil and vegetation.
8. When the early colonizers exclude subsequent colonists from moving into a community, this is
referred to as
a. facilitation
b. competitive exclusion.
c. secondary succession.
d. inhibition.
e. natural selection.
Answer: d. The mechanism by which early colonizers exclude other species from moving into a
community is called inhibition.
9. Which of the following statements is not true concerning island biogeography?
a. Diversity on islands is directly related to the size of the island.
b. Diversity on islands is directly related to the distance the island is from the source for
colonizing species.
c. The number of species on an island represents the balance between immigration and
extinction rates.
d. The number of species on an island increases with increasing distance from the source pool.
e. The number of species on an island increases with increasing island size.
Answer: d. The number of species on an island decreases with increasing distance from the source
pool.
10. The equilibrium model of island biogeography
a. is a method of mapping islands in the Pacific ocean.
b. is a method of identifying particular species on particular islands.
c. describes factors that influence succession on new islands.
d. describes the pattern of species types that first colonize an island.
e. predicts that the first colonizers of an island will become extinct.
Answer: c. MacArthur and Wilson developed the theory of island biogeography to explain the process of
succession on islands.
Conceptual Questions
1. Define a community and community ecology.
Answer: A community is an assemblage of many populations living in the same place at the same time.
Community ecology studies how groups of species interact and form functional communities.
2. Explain the productivity hypothesis.
Answer: The productivity hypothesis proposes that greater production by plants results in greater overall
species richness. Productivity is influenced by factors such as climate and rainfall.
3. When is a community in equilibrium?
Answer: A community is in equilibrium when no change can be detected in the number of species and
their population sizes over a given period of time.
Experimental Questions
1. What was the purpose of Wilson and Simberloff’s study?
Answer: Wilson and Simberloff were testing the three predictions of the theory of island biogeography.
One prediction suggested that the number of species should increase with increasing island size.
Another prediction suggested that the number of species should decrease with increasing distance of
the island from the source pool. Finally, the researchers were testing the prediction that the turnover of
species on islands should be considerable.
2. Why did the researchers conduct a thorough species survey of arthropods before experimental
removal of all the arthropod species?
Answer: Wilson and Simberloff used the information gathered from the species survey to determine
whether the same types of species recolonized the islands or if colonizing species were random.
3. What did the researchers conclude about the relationship between island size and species richness
and about species turnover?
Answer: The data suggested that species richness did increase with island size. Also, the researchers
found that in all but one of the islands, the number of species was similar to the number of species
before fumigation.
Collaborative Questions
1. Discuss the concept of ecological succession.
Answer: Succession is the gradual and continuous change in species composition and community
structure over time. There are two major types of ecological succession, primary and secondary.
Primary succession is succession that occurs on a newly exposed site that was not previously occupied
by soil and vegetation, such as bare ground caused by volcanic eruption or the rubble created by the
retreat of a glacier. This process takes an extremely long time, and only a very small portion of earth’s
surface is undergoing this type of succession at a given time. Secondary succession refers to
succession that occurs on a site that has already supported life but has undergone a disturbance, such
as a fire, tornado, or flood. How severe the disturbance is will dictate how far back the ecosystem will be
pushed and how long it will take until it reaches the climax or final stage of succession. This type of
succession is occurring all the time all over the world, from a small fire to the 2004 tsunami in Indonesia,
which destroyed a vast area.
2. What are the three most important hypotheses used to predict species richness?
Answer: The time hypothesis predicts that the number of species increases over time and that
temperate regions have less rich communities than tropical regions. This is due to the fact that
temperate regions have just recently recovered from a glacial period and species that could possibly live
in temperate regions have not yet migrated back into the recently exposed area. One drawback to this
hypothesis is that it has limited applications to marine ecosystems.
The area hypothesis proposes that larger areas contain more species than smaller areas because they
support a greater diversity of habitats and larger populations are less prone to extinctions. However, the
area hypothesis seems unable to explain why, if increased richness is linked to increased area, there
are not more species in the vast contiguous landmass of Asia, large areas with low species richness.
The productivity hypothesis proposes that greater production by plants results in greater overall species
richness. An increase in plant biomass leads to an increase in the number of herbivores and hence an
increase in the number of predator, parasite, and scavenger species. There are exceptions to this
hypothesis. For example, there are parts of the tropical seas that have low productivity but high
richness, and parts of the sub-Antarctic that have high productivity but low species richness.
Since there are exceptions to each of these hypotheses, it is likely that for any given point on earth,
species richness may be affected by the interaction of several different factors.