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1. The diagrams below show the species found in two communities located in different parts of an
African savannah. Each animal represents 25 individuals.
Which statement best describes these two communities in terms of species richness (number of
different species), relative abundance, and species diversity?
(A) Both communities have the same species richness and species diversity; however,
community 2 has a higher relative abundance in all but one species when compared to
community 1.
Distractor Rationale:
This answer suggests the student may understand that the same six species are found in
both communities and that relative abundance is the number of organisms in each species
compared to the total number of organisms in the community, but does not understand
that community 1 has a lower relative abundance of all but one species, and therefore a
lower species diversity than community 2.
(B) Community 2 has a higher species richness, relative abundance, and species diversity when
compared to community 1.
Distractor Rationale:
This answer suggests the student may understand that species diversity and relative
abundance are related to the relative population of each species, but does not understand
that species richness is the number of different species in a community or that the species
richness is the same in both communities.
(C) Both communities have the same species richness; however, community 2 has a higher
relative abundance in all but one species and a greater species diversity than community 1.
4.12 A: Quantitative Measures of Community Structure Quiz
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Rationale:
This answer suggests the student understands that species richness is the total number of
different species and that the species diversity of a community depends on both species
richness and relative abundance of each species.
(D) Community 1 has a dominant species, but has the same species richness, relative
abundance, and species diversity as community 2.
Distractor Rationale:
This answer suggests the student may understand that there is a dominant species in
community 1, but does not understand how a dominant species affects species diversity
measurements by lowering the relative abundance of each of the other species and lowers
the species diversity of community 1 when compared to community 2.
Aligned to: LO 4.12 CA 4.12: Apply Math to Community Interactions
2. Since the reintroduction of wolves to Yellowstone National Park in 1995, scientists have observed
many changes in the park’s ecology. The elk population decreased, so the elk are no longer a
limiting factor on plants and tree saplings in open areas or near rivers and streams. This has
allowed trees and shrubs, including aspen, willow, and cottonwood, to begin growing alongside
rivers and streams, and led to an improved habitat for beaver and fish. The coyote population
decreased, which has enabled small mammal populations, such as mice and rabbits, to increase
and provide other small predators, such as red foxes and bald eagles, with a more abundant food
source.
Based on the scientists’ observations, which graph most accurately shows a relationship in
Yellowstone National Park?
(A)
Rationale:
This answer suggests the student understands that there is a negative relationship
between the elk population and species diversity based on the observations of the effects of
elk overgrazing.
4.12 A: Quantitative Measures of Community Structure Quiz
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(B)
Distractor Rationale:
This answer suggests the student may understand that an increase in the number of
predators can have a negative effect on species diversity, but does not understand that
wolves have improved species diversity by reducing the elk population, or that the
observations do not indicate that an increasing wolf population is reducing species diversity
in the park.
(C)
Distractor Rationale:
This answer suggests the student may understand that species diversity can increase when
the relative abundance of organisms in a community increases, but does not understand
that the observations show that a decrease in the number of elk has had a positive effect on
species diversity.
(D)
Distractor Rationale:
This answer suggests the student may understand that an increase in the relative
abundance of a top predator can lead to a decrease in species diversity due to over hunting,
but does not understand that observations show that an increase in the number of wolves
has increased species diversity in the park.
Aligned to: LO 4.12 CA 4.12: Apply Math to Community Interactions
4.12 A: Quantitative Measures of Community Structure Quiz
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3. The ochre sea star, Pisaster ochraceus, feeds on mussels and is the dominant predator in Pacific
tide pool communities. Mussels are fast-growing mollusks that grow in colonies and can quickly
dominate tide pools. To test the effect of the ochre sea star on tide pools, scientists removed all
the ochre sea stars in one area of tide pools and compared the species richness (number of
different species) in the tide pools to that of another area of tide pools, where the sea stars were
not removed, at the beginning of the experiment and at the end of the experiment three years
later.
Based on this information, which table represents the most likely effect of the sea stars on the
tide pools?
(A)
Distractor Rationale:
This answer suggests the student may understand that sea stars prevent the mussels from
dominating tide pools, but does not understand that in the absence of sea stars, the
relative abundance of mussels in the tide pools will increase, not decrease.
(B)
Distractor Rationale:
This answer suggests the student may understand that the removal of sea stars will
increase the relative abundance of mussels, but does not understand that in the tide pools
where sea stars were not removed the relative abundance of mussels should not change.
(C)
4.12 A: Quantitative Measures of Community Structure Quiz
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Rationale:
This answer suggests the student understands that predators (sea stars) keep a prey
population (mussels) from growing rapidly and outcompeting other species for resources,
and that this encourages species diversity in the area.
(D)
Distractor Rationale:
This answer suggests the student may understand that sea stars keep the mussels from
dominating tide pools, but does not understand that the species diversity decreases in tide
pools where sea stars are removed due to the increase in the relative abundance of mussels
in the tide pools.
Aligned to: LO 4.12 CA 4.12: Apply Math to Community Interactions
4. A scientist estimates the number of crayfish in a pond using the Mark-Recapture technique.
Several traps are placed at locations around the pond and 80 crayfish are caught, marked, and
released. Several days later, the traps are reset and 30 marked and 40 unmarked crayfish are
caught. The formula the scientist uses to estimate the population using the Mark-Recapture
technique is shown below.
Which is the best estimate of the population of crayfish in the pond?
(A) 107
4.12 A: Quantitative Measures of Community Structure Quiz
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Distractor Rationale:
This answer suggests the student may understand that the Mark-Recapture formula can be
used to estimate population size, but does not understand that it requires the multiplication
of the total number of individuals captured during the first trapping (80) by the total number
captured during the second trapping (70), not the total number of unmarked individuals
captured (40).
(B) 140
Distractor Rationale:
This answer suggests the student may understand that the Mark-Recapture formula can be
used to estimate population size, but does not understand that it requires that the
numerator be divided by the number of individuals that are recaptured (30), not the number
of newly captured individuals during the second visit (40).
(C) 150
Distractor Rationale:
This answer suggests the student may understand that population size can be estimated by
counting individuals and accounting for recaptured individuals, but does not understand
that 80 crayfish are caught in the first visit, 70 total crayfish are caught on the second visit,
and 30 crayfish are recaptured on the second visit.
(D) 187
Rationale:
This answer suggests the student understands how to accurately estimate population size
using the Mark-Recapture formula.
Aligned to: LO 4.12 CA 4.12: Apply Math to Community Interactions
4.12 A: Quantitative Measures of Community Structure Quiz
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