Passage

A species that exerts. an influence out of proportion to its abundance in an ecosystem is called a k

Question

Passage

A species that exerts. an influence out of proportion to its abundance in an ecosystem is called a keystone species. The keystone species may influence both the species richness of communities and the flow of energy and materials through ecosystems. The sea star Pisaster the flow of energy and materials through ecosystems. The sea star Pisaster orchaceus, which lives in rocky intertidal ecosystems on the Pacific coast of North America, is also an example of a keystone species. Its preferred prey is the mussel Mytilus californianus. In the absence of sea- stars, these mussels crowd out other competitors in a broad belt of the intertidal zone. By consuming mussels, sea star creates bare spaces that are taken over by a variety of other species. A study at the University of washington demonstrated the influence of Pisaster on species richness by removing sea stars from selected parts of the intertidal zone repeatedly over a period of five years. Two major changes occurred in the areas from which sea stars were removed. First, the lower edge of the 46. mussel bed extended farther down into the intertidal zone, showing that sea stars are able to eliminate mussels completely where they are covered with water most of the time. Second, and more dramatically, 28 species of animals and algae disappeared from the sea star removal zone. Eventually only Mytilus, the dominant competitor, occupied the entire substratum. Through its effect on competitive relationships, predation by Pisaster largely determines which species live in these rocky intertidal ecosystems.

Which of the following is/are implied by the passage?

1. Mussels are always hard competitors for sea stars.

2. Sea stars of the Pacific coast have reached the climax of their evolution.

3. Sea stars constitute an important component in the energy flow in intertidal ecosystem.

Which of the statements given above is/are correct?

Accepted Answer

The passage defines a keystone species as one that influences "the flow of energy and materials through ecosystems." It then identifies the sea star Pisaster orchaceus as an example of a keystone species. By consuming mussels, the sea star directly participates in the transfer of energy within the ecosystem (from mussels to sea stars). This consumption also dramatically alters the community structure, which in turn influences the overall energy flow and material cycling by affecting which species are present and in what abundance. Therefore, statement 3 is directly implied by the definition and the role described for the sea star.

Let's analyze the other statements:
1. "Mussels are always hard competitors for sea stars." The passage states that mussels are the "preferred prey" of sea stars. This indicates a predator-prey relationship, not a competitive one. Mussels compete with other species for space, but not with sea stars. So, statement 1 is incorrect.
2. "Sea stars of the Pacific coast have reached the climax of their evolution." The passage discusses the ecological role of sea stars within an ecosystem. It provides no information or basis to infer anything about their evolutionary stage or whether they have reached a "climax of their evolution." So, statement 2 is incorrect.

Thus, only statement 3 is implied by the passage.

The final answer is D.

Answer

1 and 2

Answer

2 only

Answer

1 and 3

Answer

3 only

Explanation

Related questions