Between 1980 and 2000 the sea otter population

[gmatdriller]

Between 1980 and 2000 the sea otter population of the Aleutian Island 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 Island 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 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 fish use for food.

[GMATGuruNY]

Between 1980 and 2000 the sea otter population of the Aleutian Island 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 Island 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 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 fish use for food.

Conclusion: Orcas were most likely the immediate cause of the otter population decline.

In a causal argument, the conclusion is that A CAUSES B.
One way to strengthen a causal argument is to show the following:
If A does not happen, then B does not happen, STRENGTHENING the conclusion that A CAUSES B.

Answer choice C: Most of the surviving sea otters live in a bay that is inaccessible to orcas.
Implication:
If A does not happen (if orcas are unable to access sea otters), then B does not happen (the otters are not eaten), STRENGTHENING the conclusion that orcas CAUSED the decline in the otter population.

The correct answer is C.

[Jim@StratusPrep]

The argument says that orcas will eat sea otters is seals are unavailable, so we want to find a statement that says the seals are not a strong enough food source.


C says exactly this.

[Brent@GMATPrepNow]

Mitch points out one way to strengthen a cause-and-effect argument.

Two more ways to strengthen a cause-and-effect argument:
- provide additional information that supports the causal effect
- eliminate the possibility that something else causes the event.

Cause-and-effect arguments are common on the GMAT, as are statistical arguments and analogy arguments, so be sure you know how to strengthen and weaken these argument types.
We have a free video on common argument types: https://www.gmatprepnow.com/module/gmat- ... ng?id=1134

We also have a free video on strengthening the argument: https://www.gmatprepnow.com/module/gmat- ... ng?id=1138

Cheers,
Brent

[gmatdriller]

Trying to paraphrase:

In the presence of otters, there will be predation by orcas.
(provided no seals are available).

The stem went on to say seals declined dramatically, so the
absence of otters is most likely attributable to orcas.

C suggests that the surviving ones only escaped predation from otters 'cos they are
inaccessible. Thus strengthening the claim that orcas are responsible for otters decline.

Given that seals are NOT available:
If otters are available, Predation will take place by orcas (If A, then B)
If otters are NOT available, Predation will NOT take place by orcas(If NOT A, then NOT B)

Pleased to point out issues with my reasoning.

Thanks

[[email protected]]

Please explain why B is incorrect.
If I negate B i.e. to say that seals ate otters or competed with them for food,I can very well prove an alternate reason for the decline of otter population.
Although this argument is faulty when compared with the premise that seal population is also declining.Yet is it sufficient to eliminate B based on that.
If not then please specify the POE for B.
Cheers!

[GMATGuruNY]

Please explain why B is incorrect.
If I negate B i.e. to say that seals ate otters or competed with them for food,I can very well prove an alternate reason for the decline of otter population.
Although this argument is faulty when compared with the premise that seal population is also declining.Yet is it sufficient to eliminate B based on that.
If not then please specify the POE for B.
Cheers!

Your reason for eliminating B is correct.
Premises:
The Aleutian Island seal population declined dramatically IN THE 1980s.
BETWEEN 1980 AND 2000 the sea otter population of the Aleutian Island declined precipitously.
Since few seals remained after 1980, the decline of the otter population cannot be attributed to the seals.
Thus, the information in B is irrelevant.
Eliminate B.

[RBBmba@2014]

Premises:
The Aleutian Island seal population declined dramatically IN THE 1980s.
BETWEEN 1980 AND 2000 the sea otter population of the Aleutian Island declined precipitously.
Since few seals remained after 1980, the decline of the otter population cannot be attributed to the seals.
Thus, the information in B is irrelevant.
Eliminate B.

I got the above explanation, but just would like to know - is the following interpretation of B correct ?

We don't have any info whether the population of SEALS increased post-1980s and before 2000! Even if population of SEALS had increased post-1980s and before 2000, then also B would NOT have STRENGTHENED the CONCLUSION that orcas were most likely the immediate cause of the otter population decline. (It might be because of some other PREDATORS in the sea...not conclusive yet!)

So, Option B doesn't really affect the CONCLUSION!

Correct me please if wrong!

[DavidG@VeritasPrep]

We don't have any info whether the population of SEALS increased post-1980s and before 2000! Even if population of SEALS had increased post-1980s and before 2000, then also B would NOT have STRENGTHENED the CONCLUSION that orcas were most likely the immediate cause of the otter population decline. (It might be because of some other PREDATORS in the sea...not conclusive yet!)

So, Option B doesn't really affect the CONCLUSION!

Correct me please if wrong!

Well, it's true that we don't necessarily know what happened to the seal population in the 90's, but because we're told that the seal population decreased dramatically in the 80's, there's nothing in B that would cause us to consider the possibility that seals made a dramatic recovery before 2000. But you're right, even if the seal population had miraculously rebounded, it wouldn't matter. If anything, it would weaken the conclusion, as the argument is predicated on the notion that the Orcas shifted their attention to otters because there were fewer seals to eat.

[RBBmba@2014]

We don't have any info whether the population of SEALS increased post-1980s and before 2000! Even if population of SEALS had increased post-1980s and before 2000, then also B would NOT have STRENGTHENED the CONCLUSION that orcas were most likely the immediate cause of the otter population decline. (It might be because of some other PREDATORS in the sea...not conclusive yet!)

So, Option B doesn't really affect the CONCLUSION!

Correct me please if wrong!

Well, it's true that we don't necessarily know what happened to the seal population in the 90's, but because we're told that the seal population decreased dramatically in the 80's, there's nothing in B that would cause us to consider the possibility that seals made a dramatic recovery before 2000. But you're right, even if the seal population had miraculously rebounded, it wouldn't matter. If anything, it would weaken the conclusion, as the argument is predicated on the notion that the Orcas shifted their attention to otters because there were fewer seals to eat.

ABSOLUTELY.

Even if seals don't eat otters (as given in B), that doesn't NECESSARILY mean that Orcas ate otters. Right ?

[DavidG@VeritasPrep]

We don't have any info whether the population of SEALS increased post-1980s and before 2000! Even if population of SEALS had increased post-1980s and before 2000, then also B would NOT have STRENGTHENED the CONCLUSION that orcas were most likely the immediate cause of the otter population decline. (It might be because of some other PREDATORS in the sea...not conclusive yet!)

So, Option B doesn't really affect the CONCLUSION!

Correct me please if wrong!

Well, it's true that we don't necessarily know what happened to the seal population in the 90's, but because we're told that the seal population decreased dramatically in the 80's, there's nothing in B that would cause us to consider the possibility that seals made a dramatic recovery before 2000. But you're right, even if the seal population had miraculously rebounded, it wouldn't matter. If anything, it would weaken the conclusion, as the argument is predicated on the notion that the Orcas shifted their attention to otters because there were fewer seals to eat.

ABSOLUTELY.

Even if seals don't eat otters (as given in B), that doesn't NECESSARILY mean that Orcas ate otters. Right ?

Correct.