Q18 - A stingray without parasites is

[pistachio2014]

I'm having trouble with this question. Not sure why we can say that the correct answer is choice A.
I think I'm having difficulty in connecting the correct answer to the stimulus. Choice A talks about the time during the parasites' life cycle that requires hosts other than stingrays. But the stimulus specifically says "the lack of parasites in stingrays in an indicator that the ecosystem...is under environmental stress." It seems like they are different parts of the parasites life cycle, one that needs shrimps/oysters as host, one that needs stingrays as host.

[aileenann]

You may feel a little uncomfortable with (A) because it's bringing in some specific examples of ideas rather than using the more general tone we see in the stimulus.

So how do we explain that stingrays without parasites are generally healthier than stingrays with parasites even though a lack of parasites may indicate an environmental problem, which doesn't sound like such a healthy thing? That's our task. (A) provides one mechanism - not the only possibly mechanism but an adequate one - to explain both how it could be healthier for the stingrays even though it simultaneously indicates a bigger problem. In particular, this is saying sure stingrays have parts of their lifecycle when they are healthier and parasite free, but then the parasites must be elsewhere. (A) explains where the parasites are when they aren't on the stingrays and also explains why the parasites missing is also a symptom of environmental problems.

Does that make sense? Let me know what you think

[Greatsk8erman]

I'm sorry but I still don't understand how shrimp or oysters being attacked by parasites explains the cause for a stressed-out environment that may have pollution. So during the parasites lifecycle when they were feeding on the shrimp and oysters is the exact time that something in the environment caused the death of the shrimp and oysters which essentially wiped out the parasites too, allowing the stingrays to have a lack of parasites? And this is explaining how this is an indicator of a stressed-out environment? I just don't see how this answer choice allows for a possible cause of the discrepancy. The answer choice says that the shrimp and oysters are environmentally vulnerable, but if the environment was stressed-out by something like pollution, wouldn't that mean that the oysters and shrimp would die off since they are weak and they would flood to the stingrays as a host? How on earth is this even the right answer? If anything this answer choice would cause a thriving, healthy environment, because if shrimp and oysters as hosts are allowing the stingrays to be freed up as a host, this must mean that the environment is clean or at least healthy in some way for the weak, vulnerable hosts that would not live through a wave of pollution or something of the sort. I am trying not to over think this one, but if I put a little less thinking into it, it doesn't look any better. Can someone seriously please explain this to me, I would greatly appreciate that!

[ManhattanPrepLSAT1]

Let's set up the two claims that need to be reconciled. And remember the correct answer doesn't need to completely reconcile the two claims, it just needs to "help" reconcile the two claims.

1. Stingrays are healthier without parasites than with parasites.
2. Stingrays without parasites are an indicator that the environment in which stingrays live may be under environmental stress.

To do this I think it's important to first formulate what we're trying to accomplish with the correct answer. How can it be that the presence of parasites on stingrays is both a positive indicator and a negative one? The best way is to remember that what's good for the stingrays is not always in line with what's good for the environment in which the stingrays inhabit. So if, as answer choice (A) suggests, the parasites need other hosts that might be indicators of the overall health of the environment, then the absence of the parasites, while a good thing for the stingrays, could be a bad thing when measuring the health of the environment in which the stingrays inhabit.

Answer choice (A) is not a great answer choice, but it does help us see that the absence of parasites on stingrays is not just a good thing for the stingrays, but might also indicate a bad thing for the environment. This would accomplish the goal we set out at the beginning.

Does that help clear this up? If you still see it a bit differently, please let me know. And maybe tell me how you see it, so I can follow your logic.

[richtailkim]

Here is why I thought (A) was the right answer.

If the parasites of stingrays require as hosts other organisms (shrimp and oysters) for a part of their life cycles, (as stated by the answer choice (A)), and if those organisms are environmentally vulnerable, then if the environment were to deteriorate, it could cause those organisms, in this case, shrimp or oysters, to die. But if the parasites of stingrays require shrimp or oysters as hosts in order to live, then the parasites of stingrays could also die if the environment deteriorates, since there aren't enough shrimp and oysters serving as hosts.

From all this, we can conclude that if there are far less parasites found in stingrays than normal, then we have at least some support for concluding that there is environmental stress in the ecosystem since that would be one way that there may have been a decrease in the number of shrimp and oysters, which, as pointed out earlier, are required for the parasites to survive.

I do think that this is an especially weak example of probabilistic (or inductive) reasoning, which is what makes this question difficult, but (A) does at least make sense.

[griffin3575]

After reading the above explanations and staring at this problem for a good half hour, I was still a little confused. I think some formal logic will really clear answer choice A up, as it did for me. We need to reconcile the fact that a lack of parasites can both lead to healthy stingrays while also indicating a stressed environment for the stingrays. How can a lack of parasites both help and hurt the stingrays? Wouldn't a stressed environment cause harm to the stingrays? Not necessarily. I thought it must be true that the env. stress does not actually harm the stingrays.

answer choiceA
~Parasites --> Healthy Stingrays
Parasites --> Shrimp and Oysters
Env. stress --> ~Shrimp and Oysters

Thus, Env. Stress-->~S and O--> ~parasites --> Healthy Rays
and: Env Stress--> healthy Rays

Therefore, Environmental stress doesn't actually cause harm to the stingrays, it helps them by eliminating the parasites. This allows a lack of parasites to both indicate a stressed environment while also leading to healthy stingrays without there being a contradiction, because the env. stress does not negatively effect the stingrays.

Think of it this way, does a stressed env necessarily lead to all the animals in that environment being harmed? Probably not. We cannot assume that just because the stingray's env is under stress that the stingrays are being harmed. It it quite the contrary, it's actually helping the stingrays.

[asafezrati]

The discrepancy is very vague. I don't understand how you got to the ones stated in the former posts.
How do the first and second sentences conflict with each other? It seems that you have to build a story in your head to get to that point in which they conflict.

Help?

[maryadkins]

On these Paradox or Discrepancy questions, there is ALWAYS going to be a conflict. So yes, if you don't see one, you have to find one. Sometimes you will have to work harder to find the paradox/discrepancy than other times. Here, the only one that makes sense is that the parasites have both positive and negative associations. To me, this is an especially tricky one though.

[jm.kahn]

I was troubled by choice A because it requires the assumption that the absence of the sufficient condition (parasites) would lead to the absence of the necessary condition (hosts shrimp and oysters). We know that doing so is a fallacy, but choice A requires this fallacy in order to be the credited choice.

Choice A: parasites -> environmentally vulnerable hosts shrimp/oysters

Assumption made in order to resolve paradox: ~parasites -> ~hosts shrimp/oysters
This assumption is a fallacy.

Is this a reason to challenge the credited choice?