A basic principle of ecology is that population size is partly

Question

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 
 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 
 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 
 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 
 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 
 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 
 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 
 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

Sajjad1994 · Accepted Answer

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?

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

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.

Hope it helps

Kamal1

Can someone help with Q2 ?
Confused between A and C

ANSWER: C

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

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

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.

ANSWER: D

5) The author of the passage is primarily concerned with

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.

ANSWER: A

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

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.

ANSWER: C

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

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.

ANSWER: E

Hope it helps

blueshores · Answer

Could you explain why the anwer for Q) 1 is b

Mohammad Ali Khan · Answer

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.

Posted from my mobile device

Kamal1 · Answer

Can someone help with Q2 ?
Confused between A and C

Sajjad1994 · Answer

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

Can someone help with Q2 ?
Confused between A and C

Hope it helps

BruhPoseidon · Answer

In paragraph 2 the relevant lines just say "Since the timing of reproduction is crucial to the short-lived vole", it never states the reason why it is crucial. But then again there is no better option as the passage doesn't provide specific information for any of the other options imo.

egmat · Answer

Hi BruhPoseidon,

You've actually pinned down the right instinct: on a "which question does the author  answer " question, B only wins if the passage genuinely gives the reason. So let's look at whether it does.

The key sentence is:

" 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."

Here's the piece you're skipping: the reason  why  timing matters is packed into that same sentence. Read the clause that follows "crucial":

- the vole is  short-lived , and
- the  onset of vegetative growth may be considerably delayed .

Put those together and the "why" falls out: a short-lived animal only gets a narrow window, and food (new vegetation) may show up late - so reproduction has to be timed to line up with when food actually becomes available. That  is  the answer to "Why is the timing important?" The passage doesn't wave a flag saying "here is the reason," but the "Since... in an environment in which..." structure delivers it.

Quick way to feel this move:  take a plain sentence -  "Since umbrellas are useless once you're already soaked, buying one early is wise."  Nobody spells out "the reason umbrellas must be bought early is X," yet the sentence clearly tells you  why : they don't help after you're wet. Same reading move as the vole line.

And as you noted yourself, the other choices genuinely aren't answered - the mechanism of  6-MBOA  (D), the cause of the hare boom (E, "for reasons that are unclear"), and so on. So B isn't just the least-bad option; the reason really is stated. That's why  B  holds.

Answer: B

A basic principle of ecology is that population size is partly

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GMAT Reading Comprehension (RC) Questions

A basic principle of ecology is that population size is partly

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615 to 715 in 15 Days (Ria's Strategies)

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