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patto
Joined: 22 Jun 2017
Last visit: 09 Jul 2021
Posts: 236
Given Kudos: 149
Location: Argentina
Schools: HBS '25 Wharton '25 Stanford '25
GMAT 1: 630 Q43 V34
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28 Feb 2019, 16:22
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
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According to the “bottom-up” theory of how ecosystems are structured, the availability of edible plants is what primarily determines an ecosystem’s characteristics since it determines how many herbivores the ecosystem can support, which in turn determines how many predators it can support. This theory also holds that a reduction in the number of predators will have little impact on the rest of the ecosystem.
Which one of the following, if true, would provide evidence against the bottom-up theory?
(A) In an effort to build up the population of a rare species of monkey on Vahique Island, monkeys were bred in zoos and released into the wild. However, the effort failed because the trees on which the monkeys fed were also nearly extinct.
(B) After hunting virtually eliminated predators on Rigu Island, the population of many herbivore species increased more than tenfold, causing the density of plants to be dramatically reduced.
(C) After many of the trees on Jaevix Island were cleared, the island’s leaf-cutter ants, which require a forested ecosystem, experienced a substantial decrease in population, as did the island’s anteaters.
(D) After a new species of fern was introduced to Lisdok Island, native ferns were almost eliminated. However, this did not affect the population of the herbivores that had eaten the native ferns, since they also thrived on a diet of the new fern.
(E) Plants that are a dietary staple of wild pigs on Sedif Island have flourished over the last three decades, and the population of the pigs has not changed much in spite of extensive hunting.
Which one of the following, if true, would provide evidence against the bottom-up theory?
(A) In an effort to build up the population of a rare species of monkey on Vahique Island, monkeys were bred in zoos and released into the wild. However, the effort failed because the trees on which the monkeys fed were also nearly extinct.
(B) After hunting virtually eliminated predators on Rigu Island, the population of many herbivore species increased more than tenfold, causing the density of plants to be dramatically reduced.
(C) After many of the trees on Jaevix Island were cleared, the island’s leaf-cutter ants, which require a forested ecosystem, experienced a substantial decrease in population, as did the island’s anteaters.
(D) After a new species of fern was introduced to Lisdok Island, native ferns were almost eliminated. However, this did not affect the population of the herbivores that had eaten the native ferns, since they also thrived on a diet of the new fern.
(E) Plants that are a dietary staple of wild pigs on Sedif Island have flourished over the last three decades, and the population of the pigs has not changed much in spite of extensive hunting.
02 Mar 2019, 23:21
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patto
First let us write down the BOTTOM-UP theory..
Edible plants effect herbivores -> herbivores in turn effect the number of predators. So any effect on predators will not have affect on ecosystem or plants.
We have to find the choice that weakens the theory..
Let us check each option..
Quote:
monkeys so herbivores were released in wild, but they could not survive because of lesser plants on which these monkeys could feed..
So follows the bottom-up theory.. LESSER edible plants for a species -> LESSER survival chances of the species.
Strengthens the theory
Quote:
Logic here..
Lesser predators -> more herbivores -> density of plants reduced
Opposite of bottom-up theory.
Thus, WEAKENS the bottom-up theory.
Quote:
Follows the bottom-up theory
Lesser trees->lesser ants->lesser ant eaters
Strengthens the theory
Quote:
Parallel action => introduction of a new herb<-> reduction of native herb -> no effect on herbivores as they shifted to new herb
Quote:
Extensive hunting did not effect the population of pigs. So does not challenge the bottom-up theory.
The correct answer is B
05 Mar 2019, 04:29
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patto
Bottom-up theory:
Edible plants --determine--> Herbivores --determine--> Predators
This makes sense.
A reduction in the number of predators will have little impact on the rest of the ecosystem.
This we already know is questionable - if predators reduce, Herbivores will increase so plants will reduce.
We are looking for evidence against the bottom-up theory.
(A) In an effort to build up the population of a rare species of monkey on Vahique Island, monkeys were bred in zoos and released into the wild. However, the effort failed because the trees on which the monkeys fed were also nearly extinct.
- Here we are trying to increase the population of herbivores but are unable to do so because of few plants. This is not against the bottom-up theory.
(B) After hunting virtually eliminated predators on Rigu Island, the population of many herbivore species increased more than tenfold, causing the density of plants to be dramatically reduced.
- Here, eliminating predators increases herbivores and dramatically reduces the density of plants. So reducing predators has a major impact on the rest of the ecosystem.
(C) After many of the trees on Jaevix Island were cleared, the island’s leaf-cutter ants, which require a forested ecosystem, experienced a substantial decrease in population, as did the island’s anteaters.
- Here we are told about the impact of cutting edible plants. But the theory talks about the impact of reducing predators only. Hence it doesn't conflict with our theory.
(D) After a new species of fern was introduced to Lisdok Island, native ferns were almost eliminated. However, this did not affect the population of the herbivores that had eaten the native ferns, since they also thrived on a diet of the new fern.
Here we are replacing one type of plants with another. The theory has nothing to do with that.
(E) Plants that are a dietary staple of wild pigs on Sedif Island have flourished over the last three decades, and the population of the pigs has not changed much in spite of extensive hunting.
Here we are talking about increasing plant population but the population of herbivores not increasing. Not correct.
Answer (B)
