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Between 1980 and 2000 the sea otter population of the Aleutian Islands

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Re: Between 1980 and 2000 the sea otter population of the Aleutian Islands  [#permalink]

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New post 20 Sep 2017, 23:44
Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument‘?

A. The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined. - Incorrect: Out of scope

B. Seals do not eat sea otters, nor do they compete with sea otters for food. - Incorrect: Shell game

C. Most of the surviving sea otters live in a bay that is inaccessible to orcas. - Correct: When Cause does not happen [Orcas], Effect does not happen [Otters do not diminishl]

D. The population of orcas in the Aleutian Islands has declined since the 1980s. Incorrect: Out of scope

E. An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food. - Incorrect: Out of scope
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Re: Between 1980 and 2000 the sea otter population of the Aleutian Islands  [#permalink]

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New post 24 Feb 2018, 22:52
VeritasPrepKarishma wrote:
WillGetIt wrote:
Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument‘?

A The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.

B. Seals do not eat sea otters, nor do they compete with sea otters for food.

C. Most of the surviving sea otters live in a bay that is inaccessible to orcas.

D. The population of orcas in the Aleutian Islands has declined since the 1980s.

E An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.

Please hit kudos if you like this post.


Responding to a pm:

Again, Official Answers are not debatable and really, I haven't seen an exception, at least in the verbal section.

Try to understand the logic of (C).

They have very smartly used the word: "surviving".

Let's take the argument first.

Premises:
Sea otter population declined - but no sign of disease and malnutrition so predators might have been responsible.
Seal population declined dramatically.
Orcas eat otters when seals are not available.

Conclusion:
Orcas must have led to otter population decline.

We need to strengthen that orcas are responsible for the huge decline in otter population.

C. Most of the surviving sea otters live in a bay that is inaccessible to orcas.
Had the option said, "Most sea otters live in a bay that is inaccessible to orcas," then the option would have weakened our argument.
But the option says, "Most of the surviving sea otters live in a bay that is inaccessible to orcas." This means that the otters that are left are the ones where orcas cannot reach. Wherever orcas can reach, otters have disappeared from there. It means that it is highly probable that orcas have been binging on otters wherever possible.

Imagine a meadow which was full of grass 2 months back. A small part of the meadow is fenced. Some cattle was introduced in the meadow two months back. What happens if after to months you see that most of the grass is gone except the small part which was fenced? The likely reason is that the cattle ate the grass and hence reduced it.

This is the same concept.

None of the other options are relevant.

A The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.
Irrelevant

B. Seals do not eat sea otters, nor do they compete with sea otters for food.
What seals eat is none of concern. What we need to strengthen is that orcas ate up the otters.

D. The population of orcas in the Aleutian Islands has declined since the 1980s.
This doesn't strengthen that orcas ate the otters. Perhaps some orcas couldn't adapt to decrease in seal population. We don't know.

E An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.
This might affect seal population. It doesn't strengthen that orcas ate otters.

Answer (C)


You totally cleared up my doubts on C! Thank you!
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Between 1980 and 2000 the sea otter population of the Aleutian Islands  [#permalink]

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New post 22 Feb 2019, 05:34
Explanation


Read the question first

Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat Otters when Seals, their normal prey, areunavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Analysis

Needed: A statement which strengthen the conclusion which is : Therefore, orcas were most likely the immediate cause of the otter population decline.

Stimulus already reflected that Orcas will eat Otters when their normal prey is unavailable, Now find a statement which shows that Orcas now eat Otters as Seals are not available for them.

Now look into answer choices

(A) The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.

It Neither Weakens nor Strengthen the conclusion, its just giving us a related fact. It is obvious when sea otter's population declines their prey remain alive and their number will increase. Eliminate It

(B) Seals do not eat sea otters, nor do they compete with sea otters for food.
This information is Wrongly Related, why we need to know this?. We want to know the logic which relates to Orcas vs Otters not Seals vs Otters. It's a trap answer.

(C) Most of the surviving sea otters live in a bay that is inaccessible to orcas.
Now read above what we need a statement which shows that Orcas now eat Otters as Seals are not available for them. This statement shows that Otters are being eaten by Orcas. Since only those are alive who lives in area inaccessible to orcas.

(D) The population of orcas in the Aleutian Islands has declined since the 1980s.
It is Opposite answer, it weakens the conclusion. According to this choice if orcas are declining then Otters declining population have some other reason to so.

(E) An increase in commercial ?shing near the Aleutian Islands in the 1980s caused a slight decline in the population of the ?sh that seals use for food.
It is unrelated.

ANSWER: C

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Between 1980 and 2000 the sea otter population of the Aleutian Islands   [#permalink] 22 Feb 2019, 05:34

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