#20 - Amphibian populations are declining in numbers

[Dave Killoran]

Complete Question Explanation

StrengthenX—CE. The correct answer choice is (A)

The conclusion of the argument is a partial causal statement (but, “primary cause” still suggests this is the main cause) that the depletion of the ozone layer is the primary cause of the declining amphibian population:


DO = depletion of the ozone layer
DA = decline of amphibian population

C E
DO DA


This conclusion is based on the fact that the ozone layer blocks harmful UV-B radiation, which amphibians are vulnerable to in both adult and egg form.

Although the argument mentions UV-B radiation, which may sound impressive, the structure of the reasoning is easy to follow and no knowledge of the radiation is needed. The conclusion is clearly stated and easy to spot due to the indicator “thus.” The question stem is a StrengthenX and therefore the four incorrect answers will each strengthen the argument. Look for answers that fit the five causal strengthening answer types .

Answer choice (A): This is the correct answer. The answer fails to shed any light—positive or negative—on the connection between the ozone depletion and the amphibian population decline. Because the argument is concerned with the damage done by UV-B radiation, the fact that UV-B is the only damaging type of radiation blocked by ozone is irrelevant.

Answer choice (B): This answer choice strengthens the argument by showing that when the cause is absent in nonamphibian populations, the effect does not occur (Type C).

Answer choice (C): This answer strengthens the argument by showing that the areas of ozone depletion and amphibian decline match each other, thereby affirming the data used to make the conclusion (Type E).

Answer choice (D): This was the answer most frequently chosen by test takers. This answer choice strengthens the argument by eliminating an alternate cause for the effect (Type A). Had the natural habitat become smaller over the years (from say, human encroachment or climatic change) then that shrinkage would have offered an alternate explanation for the decline in the amphibian population. By eliminating the possibility of habitat shrinkage, the stated cause in the argument is strengthened.

Some students, when considering this answer choice, question whether the size of the natural habitat of amphibians has anything to do with the population of the amphibians. This view often sounds reasonable at first, but it is one that LSAC has proven to disagree with, and one that stretches the bounds of common sense. Taking the idea to the extreme, if there was no natural habitat for amphibians, there would definitely be an effect on population. Although the degree of reduction and timing of the corresponding effect may be in question, LSAC has, in this question and in others, shown that they believe that the average person understands and accepts that habitat size does affect population.

Answer choice (E): This answer strengthens the argument by showing that the decline of the amphibians has mirrored the decline of the ozone layer, thereby affirming the data used to make the conclusion (Type E).

[curiosity]

I narrowed this question down to choices A and E. I'm wondering if you can please tell me the logic for choosing A over E. When reviewing this afterwards, I realized that the stimulus doesn't establish a causal link between "damaged genes" and "amphibian death," so knowing that UV-B is the only one that damages genes is irrelevant.

Option A also threw me off because in a lot of causal strengthen questions you have to eliminate OTHER causes for the effect, so initially I thought that was what A was doing. Can you also explain why that sort of reasoning is wrong? Thanks!

[KelseyWoods]

Hi Curiosity!

So with this question you really need to focus on the conclusion and the specific wording of it. The conclusion in the stimulus is the last sentence, after the conclusion indicator word "thus." It's a causal conclusion with "depletion of the ozone layer" given as the cause and "declining amphibian population" given as the effect.

Let's start with how answer choice (E) strengthens the argument. Answer choice (E) tells us that the amphibian population has declined continuously over the past 50 years. Since we know from the stimulus that the earth's ozone layer has been continuously depleted over the past 50 years, this answer choice shows that when we have the cause ("depletion of the ozone layer"), we have the effect ("declining amphibian population"). That is one of the 5 ways to strengthen a causal argument so it strengthens the conclusion we have in the stimulus.

Answer choice (A), however, has no effect on the argument. Again, it comes back to focusing on the conclusion. The conclusion is that the "depletion of the ozone layer," not UV-B specifically, is causing the "decline of the amphibian population." It is definitely a little confusing since most of the premises talk about UV-B specifically. That's why it's always important to focus on the precise wording of the conclusion. We're not trying to show that UV-B is causing the drop in the amphibian population, so we don't need to eliminate alternate causes to UV-B. Answer choice (A) just tells us that UV-B is the only type of radiation blocked by the atmospheric ozone that can damage genes but this doesn't strengthen our argument that "depletion of the ozone layer" is causing the "decline of the amphibian population."

Since we are looking for something which does not strengthen the argument, answer choice (A) is our correct answer.

Hope this helps!

Best,
Kelsey

[eober]

Hi,

In this question doesn't answer choice A eliminates an alternative explanation by saying that UV-B is the ONLY type that can damage genes? Does it fail to strengthen because it is not strengthening by focusing on "ozone layer"?

Thank you!

[Emily Haney-Caron]

Hi eober,

Answer A is irrelevant. Answer A is only talking about "Of the various types of radiation blocked by atmospheric ozone" and therefore does not tell us anything about types of radiation NOT blocked by the ozone.

[Sherry001]

Hello,
I found this stimulus very interesting and fun but really can't eliminate A . I feel it strengthens is.
Could you please help me get rid of it ?


1- ozone layer has been continuously deflated throughout the last 50 years.
2- ozone was to block UVB a type of ultraviolet radiation that can damage genes.
3- because amphibians lack hair, hide and etc to shield them they are particularly vulnerable to this radiation .

Conclusion : the primary cause of the declining amphibian population is the depletion of the ozone layer.

Analysis before heading to the answer choices: okay, so this is a strengthen X , so I am looking for anything that either weakens the causal statement or is irrelevant.

A) I have no idea why this is seen as irrelevant . As I see it strengthening premise 2 and 3. Suggesting that because this does indeed cause damage to their genes. I can see that it doesn't necessarily add anything new, as we already know this from the stimulus, but so does the other answer choices . So how do we get rid of this little one ?

B)strengthens
C)strengthens
D)strengthens by getting rid of alternatives
E)strengthens

Thank you
Sherry

[David Boyle]

Hello,
I found this stimulus very interesting and fun but really can't eliminate A . I feel it strengthens is.
Could you please help me get rid of it ?


1- ozone layer has been continuously deflated throughout the last 50 years.
2- ozone was to block UVB a type of ultraviolet radiation that can damage genes.
3- because amphibians lack hair, hide and etc to shield them they are particularly vulnerable to this radiation .

Conclusion : the primary cause of the declining amphibian population is the depletion of the ozone layer.

Analysis before heading to the answer choices: okay, so this is a strengthen X , so I am looking for anything that either weakens the causal statement or is irrelevant.

A) I have no idea why this is seen as irrelevant . As I see it strengthening premise 2 and 3. Suggesting that because this does indeed cause damage to their genes. I can see that it doesn't necessarily add anything new, as we already know this from the stimulus, but so does the other answer choices . So how do we get rid of this little one ?

B)strengthens
C)strengthens
D)strengthens by getting rid of alternatives
E)strengthens

Thank you
Sherry

Hello Sherry001,

Answer A doesn't tell us much we don't know already. We already know that UVB damages genes, so if it's the only type of radiation that does that, does that really make a difference?
What we need is some sort of linkage to the declining population, which is what the other answer choices give, or in the case of answer D, it shows that there isn't an alternate cause (lack of habitat).

Hope this helps,
David

[elbism]

Okay, this is my last question of the evening before I retire for the night (i'm in the UK practicing for US LSAT)

I'm having some trouble with a problem that appeared in the powerscore LR bible. It goes as followed

"
Amphibian populations are declining in numbers worldwide... [admin note: Remainder of question content removed in order to comply with LSAC copyright restrictions.] "

This is a strengthen X q, in other words we need to find an answer that does not strengthen the fact that the ozone layer is the primary cause of the declining amphibian population.

My trouble is with answer D, which is cited as an incorrect answer but for me this is unfounded.
The explanation in the book states that it's incorrect because it apparently actually strengthens the argument by eliminating an alternate cause, such as humans destroying the habitat etc.

This is the problem that I have, the rejection of (D) fails to account for a potential causal relationship between the depletion of amphibians from the ozone layer and the declining natural habitat of amphibians.

Although I'm not a scientist, i am briefly aware of Darwin's theory of evolution. At it's most basic level, the theory assumes that animals and nature develop traits and habits for survival. For example a particular insect that is often preyed upon may develop a camouflage disguise that makes it undetectable amongst tree bark etc etc.

Following this, we also know that nature is (at least in some parts) designed for the preservation of such species. Taking amphibians as an example, lily pads are specifically designed to protect frogs from prey. Since lily pads exist for the purpose of protecting a particular animal, it makes sense thusly that if the particular animal was to become extinct then (at least according to Darwin) overtime the habitat designed to protect it would too, naturally begin to decline. (Even as a contrapositive LP -> F, F/ -> /LP)

Now, I know the LSAT test makers do not expect us to have in depth knowledge of science to the degree of knowing the length of time it would take for such changes to take effect, but since the study was conducted over 50 years, one might assume that if, say, on the extreme end, 95% of amphibians had been extinct towards the early years of the study (due to the ozone layer damage) then at the end of those 50 years, the natural habitat COULD have reduced by at the very least 1% naturally, due to the decline in amphibians (lily pads no longer having a use) - due to the damage of the ozone layer. (If it were to have reduced by at least 1% the test makers would not be justified in using the term 'not', and should instead adopt a broader term such as 'hardly' - and with more clarity, eg "the natural habitat of amphibians has hardly declined from natural causes"). This would be acceptable, in my opinion.

the answer that does support the aforementioned would be "the habitat has become smaller", so therefore "the habitat has not become smaller" should suffice as an answer that does the opposite of strengthen. In other words, if this theory is true, D should actually weaken the stimulus, because it would suggest that if their habitats are still exactly in tact, then amphibians can not be declining, otherwise it's habitat would surely follow suit, over a period of time. Thus conforming to the 'strengthen except' criterion.

This is also particularly due to the fact the the language is so strong and says it has "not" become smaller (meaning it does not even allow for a 0.5% natural reduction).

Maybe such changes are that which would occur only over hundreds of thousands of years, but this shouldn't be information that has to be looked up because if it isn't 'common knowledge' it isn't fair to expect us to know it.

I hope this makes sense! Thanks.

[Robert Carroll]

elbism,

The information and logic you came up with regarding evolution is interesting, and I'm not qualified to judge it, but I can judge its validity on the test! It's extraneous information that you can't assume - while it may be true in reality, the testmakers don't assume its truth or falsity because it's information brought in from the outside.

Thus, you can't assume that if a species declines, its habitat will also decline. It's simply outside information, a worthy topic for a science class but not something you should use on the LSAT itself.

So, while the natural habitat may or may not be affected by ozone, these amphibians' decline is something the stimulus provides one explanation for - depleted ozone layer - but for which there are multiple alternative explanations. One of those is that the habitat is becoming smaller. As you pointed out, and this IS ok to consider, the habitat may decline because of the depleting ozone layer. On the other hand, it may decline for unrelated reasons. The point is that the habitat's becoming smaller may be a cause unrelated to the ozone layer, which would independently account for the amphibians' decline. Whether or not we can tell that it is independent, its very possibility makes it tough to say whether the author of the stimulus is right that the depleted ozone layer is the primary cause of the amphibians' decline. Because of that uncertainty, we'd feel a lot better about the conclusion if we could just get rid of the alternative explanation entirely - and that's what answer choice (D) does.

Robert Carroll

[elbism]

I understand. I would be happy if the correct answer weakened the stimulus to a greater extent, however the correct answer is A because it has no impact on the stimulus at all - therefore does not strengthen it.

So now if it's between A - neutral and D -maybe strengthen, maybe weaken,
and we need to conform to the uniqueness rule of the correct answer, does that mean that a 'neutral' response conforms more with 'not strengthening' than does a 'perhaps strengthening', 'perhaps not' answer? - if that's the case, i suppose it would clear up a lot.

it can just be confusing if you go to the extent of averaging a 'maybe yes' 'maybe no' answer to a neutral answer for lack of better logical deduction abilities