bySayantani Barman Experta en el extranjero
Reading Passage 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.
‘A basic principle of ecology is that population size is partly’ is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.
This GMAT Reading Comprehension consists of 7 comprehension questions.
The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analysing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.
Questions and Solutions
- 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?
Answer: B
Explanation: (A) is incorrect because it deviates from this. The author spends many words at the end of paragraph 2 elaborating on the significance of time for vole reproduction. This means that option (B) appears to be the best choice. Simply put, (C) is never covered. Because the author emphasises the importance of 6-MBOA but not its biological process, (D) is incorrect. The third paragraph of (E) dismisses the explanation for the hares' overpopulation by using the phrase "for reasons that are unclear." The response is (B).
- 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
Answer: C
Explanation: According to the given passage, time is essential because voles have a short lifespan and plant growth timing is unpredictable. The link between plants and rodents suggests that vole populations rise during periods of increased food availability. The best way to restate this conclusion is (C). (A) makes a mistaken turn. 6- MBOA encourages reproduction rather than discouraging it. There is no mention of (B), (D), or (E) anywhere.
- Which of the following statements can be inferred about plant shoots containing large amounts of terpene and phenolic resins?
- They serve as a form of natural defense.
- Their growth is stimulated by increases in the hare population.
- They are unappetizing to hares.
(A) I only
(B) II only
(C) III only
(D) I and III only
(E) I, II, and III
Answer: D
Explanation: The third paragraph talks about the resinous shoots. These shoots serve as "a phytochemical defence against the depredations of snowshoe hares in Canada," according to the information provided there. This proves that my first assertion is true. Additionally, we are informed that hares avoid shoots that have been intentionally treated with these resins. This is because the resins in these shoots "discourage hare browsing." This implies that the right response must also include assertion III. However, statement II is not supported by the passage because it does not state that rising hare populations induce plants to grow more resinous shoots. Consequently, the response is (D).
- 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
Answer: D
Explanation: Berger should study lemmings since they resemble voles. (A) and (B). (E) disagrees. Author seeks to prove, not disprove. (C) supports Berger's findings, and (D) indicates whether they can be generalised. The paragraph assumes Berger's vole results. Lemmings, like voles, may be triggered by plants. (D) Berger's findings may apply to other species.
- 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
Answer: A
Explanation: The solution to this general question must address the intricate connection between food and population size. It must be taking into account the rodent instances, and it must cover the entirety of the paragraph. So, the ideal response is (A). Only the second paragraph contains the detail (B), and only paragraph three contains the detail (E). (C) is too broad, while (D) brings up a subject the author never discusses.
- 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
Answer: C
Explanation: You will see that Bryant's conclusion is just conjecture when you read about the hares. He deduces that the lack of consumption of resinous shoots by hares "may play a role" in the population drop. It is presumable that a decline in population is related to people not eating plants. The avoidance of plants would result in famine and a fall in population, as indicated by choice (C).
- 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
Answer: E
Explanation: Choice (A) was a component of both—Berger examined changes in breeding behaviour in voles and Bryant observed changes in feeding behaviour in hares. Both also include (B): Bryant examined hare populations whereas Berger tracked changes in vole populations. Since both scientists fed the animals chemically altered food and recorded intake, (C) and (D) apply to both studies. This is true: (E).
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