Although numbers of animals in a given region may fluctuate from year

Question

Although numbers of animals in a given region may fluctuate from year to year, the fluctuations are often temporary and, over long periods, trivial. Scientists have advanced three theories of population control to account for this relative constancy.

The first theory attributes a relatively constant population to periodic climatic catastrophes that decimate populations with such frequency as to prevent them from exceeding some particular limit. In the case of small organisms with short life cycles, climatic changes need not be catastrophic: normal seasonal changes in photoperiod (daily amount of sunlight), for example, can govern population growth. This theory—the density-independent view—asserts that climatic factors exert the same regulatory effect on population regardless of the number of individuals in a region.

A second theory argues that population growth is primarily density-dependent—that is, the rate of growth of a population in a region decreases as the number of animals increases. The mechanisms that manage regulation may vary. For example, as numbers increase, the food supply would probably diminish, which would increase mortality. In addition, as Lotka and Volterra have shown, predators can find prey more easily in high-density populations. Other regulators include physiological control mechanisms: for example, Christian and Davis have demonstrated how the crowding that results from a rise in numbers may bring about hormonal changes in the pituitary and adrenal glands that in turn may regulate population by lowering sexual activity and inhibiting sexual maturation. There is evidence that these effects may persist for three generations in the absence of the original provocation. One challenge for density-dependent theorists is to develop models that would allow the precise prediction of the effects of crowding.

A third theory, proposed by Wynne-Edwards and termed “epideictic,” argues that organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint. However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies.   1 
 1. The primary purpose of the passage is to

(A) argue against those scientists who maintain that animal populations tend to fluctuate
(B) compare and contrast the density-dependent and epideictic theories of population control
(C) provide example of some of the ways in which animals exercise reproductive restraint to control their own numbers
(D) suggests that theories of population control that concentrate on the social behavior of animals are more open to debate than are theories that do not
(E) summarize a number of scientific theories that attempt to explain why animal populations do not exceed certain limits

2 
 2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to

(A) use their theory to explain the population growth of organisms with short life cycles
(B) reproduce the results of the study of Christian and Davis
(C) explain adequately why the numbers of a population can increase as the population’s rate of growth decreases
(D) make sufficiently accurate predictions about the effects of crowding
(E) demonstrate how predator populations are themselves regulated

3 
 3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.
(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease.
(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase.
(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.
(E) After the number of eagles in Montana decreases, the food supply of this population of eagles also begins to decrease.

4 
 4. According to the Wynne-Edwards theory as it is described in the passage, epideictic behavior displays serve the function of

(A) determining roosting aggregations
(B) locating food
(C) attracting predators
(D) regulating sexual activity
(E) triggering hormonal changes

5 
 5. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with

(A) complete indifference
(B) qualified acceptance
(C) skeptical amusement
(D) perplexed astonishment
(E) agitated dismay

6 
 6. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?

(A) Thus Wynne-Edwards’ theory raises serious questions about the constancy of animal population in a region.
(B) Because Wynne-Edwards’ theory is able to explain more kinds of animal behavior than is the densitydependent theory, epideictic explanations of population regulation are now widely accepted.
(C) The results of one study, for instance, have suggested that group vocalizing is more often used to defend territory than to provide information about population density.
(D) Some of these studies have, in fact, worked out a systematic and complex code of social behavior that can regulate population size.
(E) One study, for example, has demonstrated that birds are more likely to use winter-roosting aggregations than group vocalizing in order to provide information on population size.

DmitryFarberMPrep · Accepted Answer

6. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?

(A) Thus Wynne-Edwards’ theory raises serious questions about the constancy of animal population in a region.
(B) Because Wynne-Edwards’ theory is able to explain more kinds of animal behavior than is the densitydependent theory, epideictic explanations of population regulation are now widely accepted.
(C) The results of one study, for instance, have suggested that group vocalizing is more often used to defend territory than to provide information about population density.
(D) Some of these studies have, in fact, worked out a systematic and complex code of social behavior that can regulate population size.
(E) One study, for example, has demonstrated that birds are more likely to use winter-roosting aggregations than group vocalizing in order to provide information on population size.

Wynne-Edwards's theory says that animals use social displays to convey information about population size. The paragraph ends by saying that this view has been challenged. 6C provides an example of such a challenge: a study that suggests a different purpose for group vocalization, one of the social displays that Wynne-Edwards addresses. E might look tempting, but it merely compares the frequency of two such displays. It still supports the idea that these displays are used for conveying information about population. The other choices all seems to support or build on the theory rather than refute it.

GMATNinja · Answer

Question 3 
 
You are correct in pointing out that the passage only discusses the density-dependent theory in the case of growth rate decreasing as the number of animals increases. However, the overall purpose of the passage is to present theories explaining the  "relative constancy"  of animal populations in a given region. With this broader purpose in mind, it is not a huge assumption to apply the density-dependent theory to a case in which the number of animals is decreasing and infer that the growth rate will increase.

In addition, by using the process of elimination it is clear that no other answer choice supports the density-dependent theory at all. Even if (A) requires a small leap of logic, it is without a doubt the correct answer because the other answer choices can be definitively eliminated.

Question 4 
 
Question #4 asks what function "epideictic behavior displays" serve. In other words,  what is the purpose  of these behaviors?

In the last paragraph the author explains that, according to the epideictic theory, "organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint."

So, animals have developed certain behaviors in order to spread information about population size. The  purpose  of spreading this information is to allow organisms to limit the population by having fewer offspring.

Let's first look at (A):
 
The passage discusses winter-roosting aggregations as an  example  of an epideictic behavior, but the  purpose  of this behaviors is not "determining roosting aggregations." As discussed above, these behaviors are used to allow organisms to make the decision to have fewer babies. So, (A) does not reflect the function served by epideictic behaviors.

Now take a look at (D):
 
This aligns nicely with our analysis above -- the function of epideictic behaviors is to allow organisms to "exercise reproductive restraint" if necessary. (D) is the correct answer to question #4.

Question 5

To answer this question, we need to find out how the author feels about the challenge posed to the Wynne-Edwards theory.

The relevant piece of the passage is the very last sentence: "However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies."

Here, the author reveals that he/she thinks that the studies challenging the Wynne-Edwards theory have  "some justification."  In looking through the answer choices, we need one that reflects this somewhat reserved support for the challenges to the theory.

The only answer choice that fits the bill is (B), "qualified acceptance." The author accepts that the challenge is justified, but qualifies (or adds conditions to) this acceptance with the modifier "some."

I hope that helps!

idivya · Answer

Hi Dmitry,

Can u plz explain why we have to search for refuting Whynne's theory option, when it is asking about continuation of the passage ??
why is D wrong here ??

Manat · Answer

i don't agree with the OA for question 3. The para states that " the rate of growth of a population in a region decreases as the number of animals increases".

The answer reverses the order to reduction in number causes an increase in rate. This is a big assumption.

Could experts please clarify. u1983, GMATNinja, SajjadAhmad, workout, GMATNinjaTwo, Gnpth

DmitryFarberMPrep · Answer

idivya , we want to refute Wynne-Edwards' theory because that's what's happening at the very end of the passage. These "continuation" questions want us to be very direct. What could we immediately attach to the end of the passage? The last sentence says that some studies have challenged W-E's theory. C follows directly upon that by providing an example of a study that contradicts his theory.

D is the exact opposite of what we want. It says that some studies have supported or extended his work. This would be like saying. "The president claims that violent crime has increased, but some studies disagree. For instance, one study showed that homicides in metropolitan areas had doubled." This directly contradicts what we'd expect, namely, a study showing that violence had gone down!

Skywalker18 · Answer

All correct in 9 mins 10 seconds, including 3 mins to read .

1. The primary purpose of the passage is to
(E) summarize a number of scientific theories that attempt to explain why animal populations do not exceed certain limits ="Although numbers of animals in a given region may fluctuate from year to year, the fluctuations are often temporary and, over long periods, trivial. Scientists have advanced three theories of population control to account for this relative constancy."

2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to
(D) make sufficiently accurate predictions about the effects of crowding - "One challenge for density-dependent theorists is to develop models that would allow the precise prediction of the effects of crowding."

3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase. -"the rate of growth of a population in a region decreases as the number of animals increases"

4. According to the Wynne-Edwards theory as it is described in the passage, epideictic behavior displays serve the function of
(D) regulating sexual activity -A third theory, proposed by Wynne-Edwards and termed “epideictic,” argues that organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise  reproductive restraint . "

5. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with
(B) qualified acceptance -"However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies."

6. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?
(C) The results of one study, for instance, have suggested that group vocalizing is more often used to defend territory than to provide information about population density.-"However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies."
The last sentence of last paragraph states that WE theory has been challenged by several studies . C goes ahead by giving an example .

blueshores · Answer

Could you explain why question 4 the answer is D and not A.
What is the difference between the 2 options.

huongguyen · Answer

2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to
 Scope line: “One  challenge  for density-dependent theorists is to  develop models  that would allow the  precise prediction of the effects of crowding .”
 
(A) use their theory to explain the population growth of organisms with  short life cycles 
(B) reproduce the results of the study of  Christian and Davis 
(C) explain adequately why the  numbers of a population can increase as the population’s rate of growth decreases 
(D) make  sufficiently accurate predictions  about the  effects of crowding 
(E) demonstrate how  predator populations  are themselves regulated

=> D

3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?
 Scope: “the rate of growth of a population in a region decreases as the number of animals increases.”
 
 (inversely proportional relationship between rate of growh & the number) 
(A) As the  number  of foxes in Minnesota  decreases , the  growth rate  of this population of foxes begins to  increase .
(B) As the  number  of woodpeckers in Vermont  decreases , the  growth rate  of this population of woodpeckers also begins to  decrease .
(C) As the  number  of prairie dogs in Oklahoma  increases , the  growth rate  of this population of prairie dogs also begins to  increase .
(D) After the  number  of beavers in Tennessee  decreases , the  number of predators  of these beavers begins to increase.
(E) After the number of eagles in Montana decreases,  the food supply  of this population of eagles also begins to decrease.

4. According to the Wynne-Edwards theory as it is described in the passage, epideictic behavior displays serve the function of
 Scope line: “such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint.”
 
(A) determining  roosting aggregations
 (B) locating  food 
(C) attracting  predators 
(D) regulating sexual activity
(E) triggering  hormonal changes

Sneha2021 · Answer

Hi Experts,
 GMATNinja   KarishmaB 
5. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with 
(A) complete indifference 
(B) qualified acceptance 
I was confused btw A and B and needs some clarity.
I agree that author has used "some justification" and this modifier hints us towards B. But if we look at the overall tone of the passage, the author simply presents 3 theories and some explanation. If we accept B, the author must have presented his view point about the challenge posed by several studies. The author says this study has provided some justification about the challenge. It doesn't cover author's inclination. That's why I think A is better than B. 
Please help me to reject A.

For Q3, why D is incorrect?
3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage? 
(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.
Bcz if no. of beavers decrease, the food availability for predators of beavers will decrease. But we cant say the no. of predators/population of predators itself will begin increasing when no. of beavers decrease. There is no relation given.

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.
- We know from the passage that "the rate of growth of a population in a region decreases as the number of animals increases" So when no. of animals increases, the growth decrease but how to derive opposite is also true (As no. decreases, the population growth rate increase)
Case 1 - No. of animals - 100 | Population Rate - 10%
Case 2 - No. of animals - 200 | Population Rate - 5%
If Case 1 to 2 is given, can we always infer case 2 to 1? I have encountered this type of relation in other CR questions too. So wanted to improve my understanding of such relation.

Thanks in advance!

KarishmaB · Answer

3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.
(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease.
(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase.
(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.
(E) After the number of eagles in Montana decreases, the food supply of this population of eagles also begins to decrease.

A second theory argues that population growth is primarily density-dependent—that is, the rate of growth of a population in a region decreases as the number of animals increases.

Density dependent theory is that 'population growth is density dependent'. The passage further explains how it is dependent. Rate of growth is inversely related to number of animals. So if number of animals increases, rate of growth decreases. Then it stands to reason that if number of animals decreases, rate of growth would increase even if it is not explicitly mentioned. Still, I would be a tad wary so would look at all options properly. If all other options are anyway incorrect, then it is fine.

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.
Correct. If number of animals decreases, growth rate increases.

(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease.
This says that if number of animals decreases, growth rate decreases. Incorrect.

(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase.
This says that if number of animals increases, growth rate increases. Incorrect.

(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.
This says that if number of animals decreases, number of predators increases. Incorrect.

(E) After the number of eagles in Montana decreases, the food supply of this population of eagles also begins to decrease.
This says that if number of animals decreases, the food supply decreases. Incorrect.

Answer (A)

KarishmaB · Answer

5. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with

(A) complete indifference
(B) qualified acceptance
(C) skeptical amusement
(D) perplexed astonishment
(E) agitated dismay

The question is not how the author regards Wynne-Edwards theory. It is how he regards the challenge posed to the theory.

However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies.

He says "with some  justification , by  several  studies". Which means he accepts the challenge but in a limited way. Hence, "qualified acceptance" is correct.

For "complete indifference" to be correct, he wouldn't give any of his own opinions on the challenge. In fact, I would think that he wouldn't even mention it if he were completely indifferent.

Answer (B)

VerbalBot · Answer

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Although numbers of animals in a given region may fluctuate from year

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Although numbers of animals in a given region may fluctuate from year

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