#26 - The three-spine stickleback is a small fish that lives

[ashpine17]

When it says larger size is better for defenses does that mean the lack of armor causes the lake stickleback to grow faster and bigger or just faster than their ocean counterparts?

[Poonam Agrawal]

Hi ashpine,

I think the answer to your question is found where it says, "Since armor limits the speed of a stickleback's growth..."

So, when the sticklebacks don't have armor, they grow in size faster than their armored counterparts. We would therefore expect an unarmored lake stickleback to be larger in size than an armored ocean stickleback of the same age.

Let us know if this is still unclear!

[qiranz]

Hi,

I am having difficulty understanding the causal relationship diagram "size is better defense no armor". The last sentence rally gives me trouble.

"Since armor limits the speed of a stickleback's growth, this indicates that having a larger size is a better defense against the lake sticklebacks' predators than having armor." Why "size is better defense" is the cause and "no armor" is the effect, not vice versa? It makes more sense to me in the stimulus that because armor limits the growth, so lake stickleback grows larger without it. I assume that without a limitation of their growing speed, we are allowed to assume that they have larger size. As a result, being larger can be a better defense for them. In other words, because they do not have armor as a defense mechanism against predators, they grow larger in size.
Moreover, the last sentence starting with a "since", a premise indicator. My brain naturally led me to think that because there is no limits on lake stickleback's growth, and therefore their sizes, we can conclude that larger size is a better defense for them.

Because I got the causal relationship reversed, it makes this question extremely challenging. Can anybody help me with the causal relationship here? Normally, the causal relationship in a strengthening question is pretty straightforward, but this one really got me!
Thank you!

[Beatrice Brown]

Hi Qiranz! Thanks for your great question, and happy to help you out with understanding this

First, let's break down the stimulus:
Premise 1: sticklebacks live in both oceans and freshwater lakes
Premise 2: ocean stickleback are covered with armor to defend against predators, but lake stickleback basically have no armor
Premise 3: armor limits the speed of a stickleback's growth
Conclusion: for a lake stickleback, having a larger size is a better defense against predators than having armor

The causal reasoning present in this argument is that the lake stickleback's lack of armor is due to the fact that size is a better defense, and since armor limits the speed of its growth, it has a lack of armor. One way to ensure that you get the direction of the causal relationship correct is by understanding what the stimulus is trying to explain. This argument is trying to explain why the lake stickleback have essentially no armor. The reason given is that having a larger size is a better defense, and if they had armor, it would limit the speed of their growth. In other words, the reason for the stickleback's lack of armor is that larger size is a better defense mechanism and no armor aids in growth.

I hope this helps, and let me know if you have any other questions on this!

[dazed&confused]

You stated that "This argument is trying to explain why the lake stickleback have essentially no armor." How did you identify that this is what the argument was trying to do? When I read it I thought the argument was simply saying why having a larger size is better for lake stickleback, rather than the way you understood it, which is that the argument is explaining why they don't have armor in the first place. This lack of understanding the purpose of the argument on my part caused me to pick answer choice C, believing that if their predators were insects, then the lack of armor is actually a hindrance. Therefore, weakening the armor which states "having a larger size is a better defense against the lake stickleback’s predators than having armor."
Can you please explain how you identified the purpose of the argument and how I can avoid this trap in the future?

[Robert Carroll]

dazed&confused,

Well, the conclusion is everything after the word "indicates". Lake stickleback lack armor but have more size. The argument seeks to explain that fact as saying that the size is a defense - they lack armor, but have size, so size must be replacing armor and performing the same role. Any other reason that lack stickleback might lack armor or have their big size would therefore weaken the argument.

Answer choice (C) just does nothing for that. Imagine lake stickleback had armor and were smaller. Would that really make them less likely to be preyed upon by insects? It seems to me a great case could be made for the opposite - armored lake stickleback, being smaller, would have been preyed upon by insects more. So size is good for their defense! There's really nothing about answer choice (C) that helps address the question of whether their larger size is a better defense than armor would have been.

Robert Carroll

[silver2731]

I'm confused.

The argument by the stimulus is:

Premise: Having armor limits the speed of growth.
Intermediate Conclusion: Thus not having armor must have been for larger size.
Main Conclusion: Thus larger size is better defense against the predator for lake stickleback.

So I think C) Having larger size is not weakening the argument.
If we negate C), having larger size is not an important factor to survive cold winters, it may be still good defense against the predators.
So the larger size still helps lake stickleback in warm region's lake against the predators. The main conclusion is not weakened.

I thought A) weakens the argument. A) is saying no it's not Size, but its for the speed of swimming. Having no armour may help speed of growth, but the main reason is for the sake of speed.
Besides, it's speed of growth. The maximum growth size can be not "large."

[Adam Tyson]

Answer A potentially strengthens the argument, silver, by showing that armor is a disadvantage when dealing with at least some predators. Since the author is trying to prove that shedding the armor and growing larger is a better defense (not necessarily a perfect one, but better than having armor) for the lake fish, anything that shows armor making them more vulnerable would help that.

I assume you meant answer B, since that's the answer that deals with colder climate and is the correct answer. We don't generally use a negation test on weaken questions, but it can shed a little light on why the answer hurts the argument. If being larger does not convey any survival advantage in colder weather, that eliminates at least one possible alternate explanation for why they don't have armor. Eliminating an alternate explanation is one way to strengthen an argument, just as offering an alternate explanation weakens an argument.

Answer B does not prove that the author is wrong, and even if it's true it could still be the case that being larger is a better defense against lake predators, but the correct answer to a Weaken question doesn't need to disprove the conclusion. It just needs to raise some doubt, and this answer does that. "Hmm, so it could be for this other reason? So it might not be about predators after all. Well now I am not so sure about this argument. Did the author overlook this other possibility?" That's all we need the answer to do, just raise a little doubt.

This is, by the way, one of the classic, common ways to weaken any causal argument. Suggesting a possible alternate cause - ANY possible alternate cause - raises at least some doubt about the causal conclusion. Possible alternate causes don't often disprove the conclusion, but they are always enough to make you go "hmm, now I'm not so sure about that."

[mkarimi73]

I recognize that there were a lot of posts on this question, so I apologize if this question was already asked. It's a simple one. When the conclusion of the stimulus says "this indicates...blah blah blah," what is it referring to? In other words, when it says "this indicates," is it referring to "lake stickleback have virtually no armor" or is it referring to "since armor limits the speed of a stickleback's growth" or both?

I ask this question because the only way to do well on LR is that you have to know EXACTLY what they are saying or else you will be misled. (I've learned that the hard way, and if you hit it on the money, the questions are much more straightforward. Translating the stimulus into your own words, WHILE also being consistent with their wording, is so so so key.) Thanks in advance!

[Robert Carroll]

mkarimi73,

"Indicates" isn't part of the conclusion at all. It's signaling that the conclusion is the proposition to follow. So everything after that word is the conclusion.

Robert Carroll