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A basic principle of ecology is that population size is partly a refle

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A basic principle of ecology is that population size is partly a refle  [#permalink]

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Updated on: 11 Sep 2019, 05:35
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New Project RC Butler 2019 - Practice 2 RC Passages Everyday
Passage # 164, Date : 23-APR-2019
This post is a part of New Project RC Butler 2019. Click here for Details

A basic principle of ecology is that population size is partly a reflection of available food resources. Recent experiments suggest that the relationship is more complex than formerly thought. Specifically, the browsing of certain rodents appears to trigger chemical reactions in food plants which, in turn, affect the size of the rodent populations. Two examples of such regulation have been reported.

Berger has demonstrated the power of a naturally occurring chemical called 6-MBOA to stimulate reproductive behavior in the mountain vole, a small mouse-like rodent. 6 MBOA forms in young grass in response to browsing by voles. Berger experimented by feeding oats coated with 6-MBOA to non-breeding winter populations of voles. After three weeks, she found a high incidence of pregnancy among females. Since the timing of reproduction is crucial to the short-lived vole in an environment in which the onset of vegetative growth may be considerably delayed, the phytochemical triggering of reproductive behavior represents a significant biological adaptation.

In an example reported by Bryant, plants appear to have developed a phytochemical defense against the depredations of snowshoe hares in Canada. Every ten years, for reasons that are unclear, the hare population swells. The result is overbrowsing of certain deciduous trees and shrubs. Bryant found that trees favored by the hare produce young shoots high in terpene and phenolic resins, which discourage hare browsing. After treating non-resinous willow twigs with resinous extracts and placing treated and untreated samples at hare feeding stations, Bryant found that samples containing at least half of the resin concentration of natural twigs were untouched. The avoidance of resinous shoots, he concludes, may play a role in the decline of the hare population to normal levels.

Both of these reports suggest areas for further research. For example, data should be reviewed to determine if periodic population explosions among lemmings (another small rodent living in a northern environment) occur during years in which there is an early onset of vegetative growth; if so, a triggering mechanism similar to that prompted by the vole may be involved.
1) The author provides specific information to answer which of the following questions?

(A) What factors other than food supply affect the population size of rodents?
(B) Why is the timing of the voles’ reproductive effort important?
(C) Are phytochemical reactions found only in northern environments?
(D) How does 6-MBOA trigger reproductive activity in the mountain vole?
(E) What are the causes of the periodic increase in the snowshoe hare population?

2) The passage describes the effect of 6-MBOA on voles as a “significant biological adaptation” (Highlighted) because it

(A) limits reproductive behavior in times of food scarcity
(B) prompts the vole population to seek new food sources
(C) supports species survival during periods of fluctuating food supply
(D) maximizes the number of offspring in individual litters
(E) minimizes territorial competition

3) Which of the following statements can be inferred about plant shoots containing large amounts of terpene and phenolic resins?

I. They serve as a form of natural defense.
II. Their growth is stimulated by increases in the hare population.
III. They are unappetizing to hares.

(A) I only
(B) II only
(C) III only
(D) I and III only
(E) I, II, and III

4) It can be inferred that the study of lemmings proposed by the author would probably

(A) strengthen the conclusions of Bryant
(B) cast doubt on the conclusions of Bryant
(C) support the specific findings of Berger
(D) provide evidence as to whether Berger’s conclusions can be generalized
(E) disprove common beliefs about the relationship between population size and food supply

5) The author of the passage is primarily concerned with

(A) reviewing findings about phytochemical regulation of rodent populations
(B) outlining the role of 6-MBOA in regulating population size
(C) summarizing knowledge on population size of rodents
(D) explaining why earlier studies of population size were wrong
(E) describing mechanisms used by plants to protect themselves

6) Bryant’s interpretation of the results of his experiment (Highlighted) depends on which of the following assumptions?

(A) The response of hares to resinous substances may be different in nature than under experimental conditions.
(B) The periodic rise in the hare population is triggered by an unknown phytochemical response.
(C) Many hares will starve to death rather than eat resinous shoots.
(D) Hares alter their breeding behavior in response to the declining availability of food.
(E) Significant numbers of hares die from ingesting the resins in shoots

7) The experiments described in the passage did each of the following EXCEPT

(A) measure changes in the behavior of test animals
(B) measure changes in the populations of experimental animals
(C) simulate a hypothesized phytochemical effect in nature
(D) measure the consumption of foods by test animals
(E) analyze the effects of food on breeding behavior

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Last edited by SajjadAhmad on 11 Sep 2019, 05:35, edited 1 time in total.
Updated - Complete topic (507).
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Re: A basic principle of ecology is that population size is partly a refle  [#permalink]

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16 May 2019, 12:07
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akansal211
SANA0203
blueshores

Here it is.

Official Explanation

Topic and Scope:

A basic scientific principle: “Population size is partly a reflection of available food resources.” Specifically, author uses two experiments (one by Berger, one by Bryant) to illustrate how changes in food supply can dramatically affect the size of rodent populations.

Purpose and Main Idea:

Author wants to demonstrate that the relationship between population and food supply “is more complex than formerly thought.”

Paragraph Structure:

In paragraph 1 the second sentence is key: “Recent experiments suggest that the relationship is more complex than formerly thought.” You can guess from these words that the passage will go on to discuss these experiments. The next sentence identifies the nature of the complexity—rodent browsing affects plant chemicals, which in turn affect the rodents.

Paragraph 2 details Berger’s experiment, which studied how plant chemicals trigger reproductive activity among voles.

Paragraph 3 details Bryant’s experiment, which studied the effect of plant chemicals on declining populations of snowshoe hares.

Paragraph 4 discusses possible future research involving lemmings, another rodent with fluctuating populations.

1) The author provides specific information to answer which of the following questions?

Difficulty Level: 750

Explanation

With a question like this, you need to check each choice against the passage. A faster way to eliminate choices is to remember that the right answer often fits with the main idea, here the food-population relationship. Thus, (A) is wrong because it ventures away from this. (B) looks excellent, because the author devotes several lines at the end of paragraph 2 to explaining the importance of timing for vole reproduction. (C) is simply never covered. (D) is wrong because the author discusses the significance of 6- MBOA, but not its biologic mechanism. With (E), why the hares overpopulate is dismissed in the third paragraph with the words “for reasons that are unclear.” The answer is (B).

2) The passage describes the effect of 6-MBOA on voles as a “significant biological adaptation” (Highlighted) because it

Difficulty Level: 700

Explanation

This question asks about a detail from paragraph 2. The cited sentence says that timing is crucial because voles are short-lived and the timing of plant growth is unpredictable. You can infer that the plant-rodent relationship increases the vole population at times when food is more plentiful. The best restatement of this inference is (C). (A) goes the wrong way. 6- MBOA triggers breeding—it doesn’t discourage it. (B), (D) and (E) are never mentioned anywhere.

3) Which of the following statements can be inferred about plant shoots containing large amounts of terpene and phenolic resins?

Difficulty Level: 750

Explanation

The resinous shoots are discussed in the third paragraph. There, we are told that these shoots function as part of “a phytochemical defense against the depredations of snowshoe hares in Canada.” This means that statement I is correct. We are also told the resins in these shoots “discourage hare browsing,” and that hares avoid shoots artificially treated with these resins. This means that statement III must also appear in the correct answer. But the passage does not say that increases in the hare population cause plants to produce more resinous shoots, so statement II is not supported by the passage. Therefore, the answer is (D).

4) It can be inferred that the study of lemmings proposed by the author would probably

Difficulty Level: 750

Explanation

The lemmings are mentioned in the last paragraph, which speculates that lemmings might, like voles, be affected by a plant trigger for breeding behavior. Some answer choices mention Berger and some mention Bryant. The lemmings are likened to voles, so Berger is the pertinent researcher here. This eliminates (A) and (B). (E) conflicts with the main idea. The author wants to prove something, not disprove it. That leaves (C), supporting Berger’s specific findings, and (D), indicating whether Berger’s findings can be generalized. The paragraph doesn’t talk about proving Berger’s specific results with the voles; those are accepted as given. It does say that the lemmings, like voles, may be affected by a plant trigger. This implies (D), that Berger’s findings may be applicable to other animals.

5) The author of the passage is primarily concerned with

Difficulty Level: 750

Explanation

The answer to this global question has to focus on something about the complex relationship between food and population size, including the rodent examples; it should also encompass the entire passage. Thus, the best answer is (A). (B) is a detail appearing only in the second paragraph, while (E) appears only in paragraph 3. (C) is too general, and (D) mentions a topic the author never covers.

6) Bryant’s interpretation of the results of his experiment (Highlighted) depends on which of the following assumptions?

Difficulty Level: 700

Explanation

When you read about the hares, notice that Bryant’s conclusion is pure speculation. He sees that the hares don’t eat resinous shoots, and concludes that this “may play a role” in population decline. The assumption is that there’s a connection between not eating the plants and a population reduction. Choice (C) corresponds: The avoidance of plants would lead to starvation, and population decline.

(A), if true, would weaken, not strengthen, Bryant’s conclusion. (B) is irrelevant—the cause of the rise is unknown and doesn’t concern Bryant; it’s the decline
that interests him. (D) mixes up the hares with the voles and their breeding behavior. The hare experiment has nothing to do with breeding and reproduction. Finally, (E) is never suggested. Bryant concluded that the population decline was caused by avoiding the shoots, not by eating them.

7) The experiments described in the passage did each of the following EXCEPT

Difficulty Level: 750

Explanation

For this question, you need to eliminate each choice that was part of both experiments. Choice (A) was part of both—Berger measured how voles changed breeding behavior and Bryant measured how hares changed eating behavior. (B) also appears in both: Berger measured the rise and fall of vole populations, while Bryant measured hare populations. (C) and (D) apply to both experiments, since both scientists fed the animals chemically treated foods and noted consumption. (E) is correct: Only Berger’s experiment dealt with the effect of food on breeding behavior. Bryant’s hare experiment dealt with the effect of food on eating behavior.

Hope it helps
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Re: A basic principle of ecology is that population size is partly a refle  [#permalink]

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12 May 2019, 08:57
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blueshores wrote:
Could you explain why the anwer for Q) 1 is b

If you read the para on an whole it discusses about the reproduction of vole.general understanding of the para should be learnt which obviously takes time to develop.

Best way to approach questions like this is to look for wrong answer choices which will help you to narrow down your search.

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Re: A basic principle of ecology is that population size is partly a refle  [#permalink]

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12 May 2019, 08:37
Could you explain why the anwer for Q) 1 is b
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Joined: 14 Aug 2018
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Schools: Erasmus '21 (S)
Re: A basic principle of ecology is that population size is partly a refle  [#permalink]

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03 Jul 2019, 01:59
Can someone help with Q2 ?
Confused between A and C
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Re: A basic principle of ecology is that population size is partly a refle  [#permalink]

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03 Jul 2019, 02:49
This question asks about a detail from paragraph 2. The cited sentence says that timing is crucial because voles are short-lived and the timing of plant growth is unpredictable. You can infer that the plant-rodent relationship increases the vole population at times when food is more plentiful. The best restatement of this inference is (C). (A) goes the wrong way. 6- MBOA triggers breeding—it doesn’t discourage it.

Hope it helps

Kamal1 wrote:
Can someone help with Q2 ?
Confused between A and C

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Re: A basic principle of ecology is that population size is partly a refle   [#permalink] 03 Jul 2019, 02:49
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