4.12 a: quantitative measures of community structure quiz

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.


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.


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.


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(B)


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)


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)


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.



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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)


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)


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)


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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)


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.


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


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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


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


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.



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4.12 a: quantitative measures of community structure quiz

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