Kate: The recent decline in numbers of the Tennessee warbler, a North

Kate::

Conclusion: Decline of Tennessee warbler is due to loss of tree cover South American coffee plantations.

Scott::

Conclusion: Warbler's decline is due to decline of population of the spruce budworm.
Premise: Spruce budworm is warbler's favorite prey in North America

Assumption1: Warblers do not have other major food source other than budworm
Assumption2: decline in favorite food source will cause Warblers to starve and decline in number.
Assumption3: Dense forest cover during migration is not important for Warbler's survival.

A. The numbers of the Baltimore oriole, a songbird that does not eat budworms but is as dependent on South America coffee plantations as is the Tennessee warbler, are declining
Strengthens conclusion 1 by giving example of another species affected for same reason but the parameter important for conclusion 2 is missing and makes the 2nd conclusion weak. Correct option
B. The spruce budworm population has dropped because of a disease that can infect budworms but not Tennessee warblers
Does not affect the 2nd conclusion
C. The drop in the population of the spruce budworm is expected to only be temporary
Irrelevant & does not affect 2nd conclusion
D. Many Tennessee warblers have begun migrating in the fall to places other than traditional coffee plantations
Irrelevant & does not affect 2nd conclusion. Does not talk about decline in number. Out of scope.
E. Although many North American songbirds have declined in numbers, no other species has experienced as great a decline as has the Tennessee warbler
Irrelevant & does not affect 2nd conclusion

A.

In my opinion, D does weaken Scott's hypothesis somewhat by suggesting another reason for the declining number of birds; however, A is a better choice because A weakens Scott's hypothesis by directly negating his argument which suggest that the declining number of the budworm is the reason for why the number of the bird is declining.

Could someone explain why #4 does not weaken Scott's argument but #1 does? I don't get it.

We have to weaken Scot's hypothesis.
Tennessee warbler is a bird dependent on dense covering in South America's coffee plantations and A points at another bird Baltimore Oriole which is similar to warbler and declining in numbers in South America's coffee plantations and it does not eat bud worms.
But B points at bud worms which are declining in North America and not in South America and most probably Warbler must be preying on something else in South,hence it cannot be B.

Hi Kotela,

In Weaken questions, there are 2 cases, either its a cause and effect or we have to hit the conclusion. In this case, we can see its a cause and effect reasoning that we have to hit. What Scott says is that because the population of budworms is declining, so the population of tenesse bird is declining. So A(budworms declining) -> B(tenesse declining). Now, we have to prove that even if A doesn't happen, B happens i.e. even if a bird is not dependent on A, that bird's numbers are also declining. So, A option wins.

Let me know if you need more clarification.

Thanks,
Amil

The correct choice in Weaken questions will provide new information that makes the conclusion less likely. Amil has provided good explanation of why choice A is correct. Even if Choice A were not there, you can see that choice B does little to weaken Scott's claim.

Scott's Claim: A(budworms declining) -> B(Tennessee Warbler declining). Note this decline is at the source (in North America). While making this statement, Scott is claiming that the population of Tennessee Warbler is declining at the source because Tennessee Warbler does not get enough food at source. Note, that Scott does not say that the cause of decline of bud-worms is the same as the cause for decline of Tennessee Warbler.


What does choice B say?

Choice B states that the cause for decline of budworms (infection) does not "directly" impact Tennessee Warbler
However, Scott never claimed the above to be the case. He only claimed that Tennessee Warbler declined because budworm declined. Hence this new information does not weaken Scott's case.

What could be another correct choice?
Any answer choice that states that the population of Tennessee Warbler is healthy in North America would be a good choice. Hence a choice that stated that the population of Tennessee Warbler in North America at the beginning of the migration period this year was no different than that last year. - would be correct.

My explanation:

Argument:
Kate : decline Tennessee is caused by elimination of dense tree
Scott: decline Tennesse is caused by decline of its prep
Prethinking: Why ? Scott’s argument is not okie ??
Keyword: elimination of dense tree.
Scopt: elimination of dense tree affects to ???
POE:
A. OK
B. Disease – out of scope
C. Out of scope
D. Out of scope
E. Out of scope

Hello experts,
I have gone through answer explanations and am convinced why OA is A. My query is argument says - elimination of dense trees - where as option A says -coffee plantations. I was trying to link former i.e cutting of trees in options. Is it safe to assume that both mean the same? Interesting to note how GMAT plays with words !

Hi adkikani, the GMAT does love to play with words, and one little word can change the entire meaning of the passage or an answer choice! First of all, be careful equating "elimination of dense trees" to "cutting of trees", since we do not know for sure how the dense trees were eliminated. All we know, based on Kate's statements, is that dense tree cover was formerly a feature of most South American coffee plantations and that this dense tree cover has been eliminated. In other words, dense tree cover is no longer a feature of most South American coffee plantations.

I'm not sure if that answers your question, so please let me know if you need further explanation. Thanks!

also, we all are missing an important reasoning error in the scott's sentence "decline in Tennesse's favorite food ...IN THE NORTH"...if the food is less in the NORTH ...the birds are more likely to move out from there ...!!!

chose A.
given that oriole does not eat budworm, it provided evidence to support kate's argument and weakens scott's explanation for the decline in warbler

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