A fourteen-year study of finches on the Galapagos islands concluded th

Question

A fourteen-year study of finches on the Galapagos islands concluded that there is a definite relationship between climate and the population size of finch species that thrive at various times. During droughts, more members of large finch species survive because their bills are large enough to crack large, hard seeds, giving them a food supply unavailable to smaller birds. In rainy years, fewer members of the large finch species survive because the additional moisture fosters the growth of plants that produce small seeds. The larger finch varieties have to consume enormous numbers of small seeds to meet their energy demands, and some just cannot eat them fast enough.

Which one of the following must be assumed in order to justify the conclusion that climatic variations cause a major difference in survival rates of small and large finches?

(A) During drought conditions, the weather promotes the growth of plants that produce small, hard seeds.

(B) A lengthy period of rainy weather results in fewer large, hard seeds being produced.

(C) In rainy periods, the small finches gather enough food to grow much larger and heavier, but their ultimate size is limited by their inability to eat small seeds fast.

(D) The Galapagos climate during this fourteen year period had about as much dry weather as it had wet weather.

(E) Small seeds do not have to be cracked open in order to be digested by any of the finch varieties.

septwibowo · Answer

Tough one, IMO difficult to solve in 2 minutes.

Waiting for OE.

stne · Answer

IMO C
If it were not the case as in C then the smaller finches would grow to become large finches and there would be no shortage of large finches even during rainy season . 
Hence it is necessary that small finches remain small , for there to a shortage of large Finches .
Then only we can attribute fluctuations in population to climate.

abrakadabra21 · Answer

In rainy years, fewer members of the large finch species survive because the additional moisture fosters the growth of plants that produce small seeds. :- Now there is nothing mentioned about large seeds. Sure, there is more smaller no. of seeds, what if there is more no. of larger seeds also.

That's a gap. that we automatically think that (or assume that) if more no. of small seeds, meaning => less no. of larger seeds.
B fill the gap.

That's a gap. that we automatically think that (or assume that) if more no. of small seeds, meaning => less no. of larger seeds. 
B fill the gap.

salviabu · Answer

Please explain each statement why its correct or wrong.

Tango3 · Answer

IMO B.. lengthy rainy season will hamper the survival of large Finch species.as mentioned in last paragraph, not all larger Finch species can gather small seeds fast.

Sent from my Moto G (4) using  GMAT Club Forum mobile app

GMATNinjaTwo · Answer

salviabu , what are your thoughts on each of the answer choices? If you explain your thought process and ask specific questions, other users will be better able to help!

ari.banerjee · Answer

Hence option B is right!

Mahmud6 · Answer

If we negate B, the conclusion falls apart. So, it is B.

A lengthy period of rainy weather results in  fewer  large, hard seeds being produced.
 Negated Statement : A lengthy period of rainy weather results in  More  large, hard seeds being produced.

If during rainy season more  large and hard  seeds are available, then larger finch varieties do not need to consume enormous numbers of  small  seeds to meet their energy demands. So, their survival rate will not decline.

Am I correct in my reasoning?

rever08 · Answer

Confused between A and B. Could someone please elaborate the difference?

srid91 · Answer

Look at option A

"During drought conditions, the weather promotes the growth of plants that produce small, hard seeds"

Let's negate it.

During drought conditions, the weather does  not  promote the growth of plants that produce small, hard seeds

Do we know the impact of small hard seeds on the conclusion that climatic variations cause a major difference in survival rates of small and large finches?
We don't. So, you can eliminate A based on this.

Remember, if you have narrowed it down to two answer choices, the negation rule will work perfectly. Never use the negation rule on all choices, it will only waste precious time.

GMATNinja · Answer

Mahmud6 , your reasoning is correct! Without the assumption stated in choice (B), we cannot eliminate the possibility that the larger finches would simply survive on large, hard seeds.

Smaller finches can survive on smaller seeds. If small seeds were produced during a drought, the smaller finches would be probably be able to survive on those seeds. The author is trying to show that smaller finches are LESS likely to survive during a drought, so choice (A) would actually work against the conclusion.

Skywalker18 · Answer

The Argument
(During droughts finches survive because they can crack large, hard seeds & during rain, there is more plants that produce small seeds)
--> 
There is a correlation between climate and population (aka, more rain causes less finches)

My Thoughts
This argument is saying that, just because there is more of one plant's seeds during rain, the finches are less likely to survive. Ummmmm what? This argument is kind of like the following: Subway chicken sandwiches are necessary for human survival. During the summer, we all eat lots of Subway chicken sandwich and everything is awesome and plenty of people make it through the summer. However, during the winter, Subway sells turkey sandwiches. Therefore, more people die. The assumption in these arguments is something like "when the rain produces these small seeds, there are less large, hard seeds." The argument is assuming that more of one thing means less of the other.

(A) Out of scope. All we need to know here is that during droughts there are enough hard seeds to go around for all the finches. It doesn't really matter what else there is because the finches are doing fine during droughts.
(B) Correct. If more rain = less large hard seeds, then we can clearly see how this would be detrimental to the finch's survival. If we negate this and say that "rainy weather does NOT result in fewer large, hard, seeds" then this would mean that there doesn't seem to be as much of a relationship between climate and survival as people think
(C) Out of scope. In the argument, we are talking about survival and not about size. This seems like a trap answer for someone that was running out of time and saw "population SIZE of finch species) and went with it. 
(D) Not necessary. We don't need to assume that there was as much of one kind of weather as the other. We are talking about what happens during those kinds of weather. It doesn't matter if that type of weather is any more or less frequent then the other type.
(E) Out of scope. We don't care if the seeds have to or don't have to be cracked open. The seeds are important not because of their "crackability" but because of their type and how available they are to these finches. There does not seem to be any correlation between "crackability" and survival

priya sri · Answer

goal-climatic variations cause a major difference in survival rates of small and large finches 
 
plan/prethink 
 
drought period-more members of large F survive- due to large ,hard seeds 
rainy season-less members of large F survive- due to small seeds growing in moisture

gap-unstated premise or bridge the gap in the argument 
 
rainy season contains small seeds 
unstated-large seeds- rain season   
 
hence we can understand,,raiy season contains no much large seeds which are feed to large F species

Laksh47 · Answer

Hi Experts,

"In rainy years, fewer members of the large finch species survive because the additional moisture fosters the growth of plants that produce small seeds"

Do we have to find an assumption in the reasoning of the above statement?

My thinking is that since this statement is a fact, we shouldn't question it's validity.

Infact, we should consider the reasoning of this fact as true (without questioning it) and then see if the conclusion i.e. "There is a def relationship bw climate and population size of finch species" has been derived correctly based on this fact, without any assumptions.

Is my thinking correct? Pls share your thoughts. Thanks

CEdward · Answer

A fourteen-year study of finches on the Galapagos islands concluded that there is a definite relationship between climate and the population size of finch species that thrive at various times. During droughts, more members of large finch species survive because their bills are large enough to crack large, hard seeds, giving them a food supply unavailable to smaller birds. In rainy years, fewer members of the large finch species survive because the additional moisture fosters the growth of plants that produce small seeds. The larger finch varieties have to consume enormous numbers of small seeds to meet their energy demands, and some just cannot eat them fast enough.

Which one of the following must be assumed in order to justify the conclusion that climatic variations cause a major difference in survival rates of small and large finches?

(A) During drought conditions, the weather promotes the growth of plants that produce small, hard seeds. X
-this is completely anti-thetical to what the passage says...during droughs, larger seeds NOT smaller seeds are made

(B) A lengthy period of rainy weather results in fewer large, hard seeds being produced. 
CORRECT. This has to be true, otherwise the birds with larger beaks would still be able to survive and the differences in survival rates would diminish.

(C) In rainy periods, the small finches gather enough food to grow much larger and heavier, but their ultimate size is limited by their inability to eat small seeds fast. X
-OK, but we already kind of knew this from the passage.

(D) The Galapagos climate during this fourteen year period had about  as much  dry weather as it had wet weather. X
-we don't care so much about the relative spits in dry vs wet weather...irrelevant

(E) Small seeds  do not have  to be cracked open in order to be digested by any of the finch varieties. X
-this weakens the argument b/c large birds would then be able to eat these smaller seeds and survive

DmitryFarberMPrep · Answer

Laksh47 
You're right--we don't want to question any of the premises of the argument. We have to accept that the rainy weather encourages the growth of plants with small seeds. We just don't know whether that hurts the birds that eat large seeds, because we don't know that one kind of plant grows  at the expense  of the other. If we can have more small-seed plants without losing large-seed plants, then the argument is much less compelling.

ravigupta2912 · Answer

The argument concludes that climatic differences are the reason for survival of different sized finches in different seasons. As support for this conclusion, it offers different diet during different climates as reason.

The question stem asks us for assumption for the above argument.

(A) During drought conditions, the weather promotes the growth of plants that produce small, hard seeds. -- Close choice. But if we read closely, it actually weakens the conclusion. If during drought conditions the weather promotes the growth of plants that produce small, hard seeds, then the small finches should logically be able to survive. So is there any other reason? We don't know. An assumption should strengthen the already provided logical reasoning of the argument (climatic changes ----> effect on survival). Eliminate. (I kept this until the last)

(B) A lengthy period of rainy weather results in fewer large, hard seeds being produced. -- Correct. This explains that the differing food available in different weathers is directly the result of climatic changes. And since the larger finches are unable to eat the small seeds quick enough, they perish in the rainy season. This assumption choice eliminates a potential weakener, which would have argued that food sources (because of which apparently the finches of different size survive) is not the result of climatic changes but something else.

(C) In rainy periods, the small finches gather enough food to grow much larger and heavier, but their ultimate size is limited by their inability to eat small seeds fast. -- I didn't understand this choice frankly. But it seems too tangential to the argument. We need to focus on strengthening the argument through finding the missing link or through eliminating a potential weakener.

(D) The Galapagos climate during this fourteen year period had about as much dry weather as it had wet weather. -- Irrelevant to the argument. Eliminate.

(E) Small seeds do not have to be cracked open in order to be digested by any of the finch varieties. -- Eliminate. "Small, hard seeds" is the phrase used. Not relevant to the argument.

YashYashkratos · Answer

it's an assumed to conclude the argument question 
 
B) if you negate B then there will be large hard seeds in the rainy weather and large flinches will feed on them and thus survive making conclusion weak

JOSH1967 · Answer

GMATNinja   DmitryFarber

While I understand why all the other options are wrong, I still need some clarification for option B. The word "lengthy period" can lead to a mild scope shift, thereby making the statement not exactly function as an assumption. Let me explain:

The negation of the statement would read, "A  lengthy period  of rainy weather results in  equal or more  large, hard seeds being produced". This may not be the case when the rainy seasons aren't lengthy or are normal, where the reported correlation still may be holding true.

Secondly, there is no guarantee that "the lengthy period" would be short enough for the existing large finches to stay alive. Maybe they died by then.

Can you please explain what I am missing? I can try explaining further if the argument isn't clear enough. Thanks in advance!

A fourteen-year study of finches on the Galapagos islands concluded th

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