I hold the opinion that some of the passages that GMAT writes are not particularly well-done...I have seen quite a few instances now where the writing was simply unclear so not sure if that is intentional or not. Give me a kudos if you agree.
1. The passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats?
(A) The degree to which the habitat is sheltered from waves
-Correct, the second last sentence mentions this explicitly
(B) The degree to which other animals within a habitat prey on mussels
-no, there is no mention of ‘other animals’ that prey on mussels
(C) The fact that mussel populations are often not dominant within some habitats occupied by P. ochraceus
-no, while the passage does mention that mussels can be a dominant population in the absence of the starfish, but this does not suggest that the mussels ARE NOT dominant, merely that they are preyed on by the keystone species
(D) The size of the P. ochraceus population within the habitat
-no, the passage does not mention this
(E) The fact that there is great species diversity within some habitats occupied by P. ochraceus
-no, species diversity in a habitat affects the keystone status of the remaining species
2. Which of the following hypothetical experiments most clearly exemplifies the method of identifying species, roles that the author considers problematic?
(A) A population of seals in an Arctic habitat is counted in order to determine whether it is the dominant species in that ecosystem,
-no, the problem occurs when there is a removal of a particular species that is involved; this choice fails to capture that
(B) A species of fish that is a keystone species in one marine ecosystem is introduced into another marine ecosystem to see whether the species will come to occupy a keystone role.
-no, the problem occurs when there is a removal of a particular species that is involved; this choice fails to capture that
(C) In order to determine whether a species of monkey is a keystone species within a particular ecosystem, the monkeys are removed from that ecosystem and the ecosystem is then studied.
-Correct
(D) Different mountain ecosystems are compared to determine how geography affects a particular species, ability to dominate its ecosystem.
-no, the passage never cites geography as one of the reasons why identifying keystone species is a problem
(E) In a grassland experiencing a changing climate, patterns of species extinction are traced in order to evaluate the effect of climate changes on keystone species in that grassland.
-no, species extinction is irrelevant
3. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?
(A) A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem.
-no, this choice fails to capture any notions about geography, community diversity, or length of interactions
(B) A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species.
Correct; one of the factors that affect keystone status is the diversity of species within a particular area; the claim is that low/a reduction in diversity leads to the emergence of a keystone species so we would expect that high diversity prevents that from happening
(C) Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.
-no, this choice fails to capture any notions about geography, community diversity, or length of interactions
(D) As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits.
-no, this choice fails to capture any notions about geography, community diversity, or length of interactions
(E) A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators.
-no, this choice fails to capture any notions about geography, community diversity, or length of interactions
4. The passage suggests which of the following about the identification of a species as a keystone species?
(A) Such an identification depends primarily on the species’ relationship to the dominant species.
-no, we don’t know whether the species’s relationship with dominant species is the PRIMARY factor
(B) Such an identification can best be made by removing the species from a particular ecosystem and observing changes that occur in the ecosystem.
-no, this is antithetical to the entire passage which suggests that by removing them it would be DIFFICULT to observe changes
(C) Such an identification is likely to be less reliable as an ecosystem becomes less diverse.
-no, this is the opposite of what the last sentence says
(D) Such an identification seems to depend on various factors within the ecosystem.
-Correct, a safe, accurate statement that is captured in the last sentence of the passage
(E) Such an identification can best be made by observing predation behavior.
-no, the example of the starfish and mussels demonstrates that using predation to study keystone status is a murky way to identify keystone species
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