According to the "bottom–up" theory of how ecosystems are structured, the availability of edible plants is what prima...

shafieiava on February 9, 2020

Answer choices B and E

Can someone explain why E is incorrect and what makes B correct answer here? Thanks in advance.

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shafieiava on February 9, 2020

As an addition to my question. Can someone confirm my understanding of why E is incorrect? Is E incorrect because it talks about the staple plant for a particular species rather than the general availability of edible plants as a whole so it is an incorrect application of the principles/premises given in the stimulus?

Skylar on February 9, 2020

@shafieiava, happy to help!

We are asked to identify the answer choice that would provide evidence against the theory presented in the passage.

(B) is correct because it shows the presence of a top-down effect. Whereas the passage states that "a reduction in the number of predators will have little impact on the rest of the ecosystem," answer choice (B) states that a dramatic reduction in the predators on Rigu Island had significant impacts on the ecosystem- making the herbivore species increase over tenfold and the plant density to be dramatically reduced. This sequence of events is opposite that presented in the passage's bottom-up theory, making (B) the best answer.

(E) is incorrect- though not for the reason you suggest. Instead, it is incorrect because it does not weaken the passage's bottom-up theory. While plants are flourishing, the population of pigs eating the plants has remained steady. However, the "extensive hunting" of these pigs could account for a pig population that was flourishing but reduced by hunting so as to seem steady. If so, the availability of plants determined the number of herbivores the ecosystem could support, and the bottom-up theory is therefore supported. Since we are looking for an answer that will provide evidence against this theory, (E) can be eliminated.

Does that make sense? Please let us know if you have any other questions!