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The three-spine stickleback is a small fish that lives both in oceans and in freshwater lakes. While ocean stickleback are covered with armor to protect them from their predators, lake stickleback have virtually no armor.
Since armor limits the speed of a stickleback's growth, this indicates that having a larger size is a better defense against the lake stickleback's predators than having
armor.
Which one of the following, if true, weakens the argument?
A) Sticklebacks with armor are unable to swim as fast, making them most vulnerable to fast-moving predators.
B) Having a larger size is an important factor in whether lake stickleback, but not ocean stickleback, survive cold winters.
C) Unlike ocean stickleback, the lake stickleback are more often preyed upon by predatory insects than by larger fish.
D) Both ocean stickleback and lake stickleback feed primarily on the same types of foods.
E) Sticklebacks originated in the ocean but began populating freshwater lakes and streams following the last ice age.
I absolutely do not understand why the correct answer is B and not C.
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7 comments
@LauraByrne Thank you so much for your explanation. Ok, I get it now. I just started the Weakening Arguments module. So basically the objective is to disrupt the premise and conclusion — that answer choice could offer an alternative conclusion and would weaken the argument.
If armor limits growth, this would mean ocean stickleback are smaller than lake stickleback. Ocean stickleback have armor to protect against predators, but what about lake stickleback? The argument assumes that their larger size plays the same role of predator defense as the ocean stickleback's armor, thus a larger size and lack of armor. However, if only the lake stickleback need to be larger to survive cold winters, then this provides an alternate explanation for why only the lake stickleback are larger and lack armor-it's not a predator defense but a climate defense. We have no idea what the impact is on predators, but maybe lake stickleback have some other defense mechanism that we don't know about. If lake stickleback are preyed on more often by insects than ocean stickleback, having a larger size wouldn't necessarily be a better defense as these insects are smaller than the stickleback, so we would have to make a pretty big assumption on how a larger size would help-much larger than the assumption that there's another explanation for their size :)
The author is concluding that larger size helps lake sticklebacks against predators more than armor.
We're looking to weaken that, so we want an answer that shows their conclusion is wrong. Probably something along the lines of how armor is actually > than size or that size is used for something other than to defend against predators
B: Explains an alternative to why sticklebacks are large. They need to be big to survive winter, not to survive against predators so the author's conclusion is wrong
C: A few reasons why it's wrong and you can pick the one that resonates with you best
We can't conclude that the difference in predators means that larger size makes them better equipped to handle insects. Anything more is speculation. Answer is neutral
This explanation, at best, shows why armor is unnecessary but not why a large size is necessary/better against the predators. Answer is neutral
Bigger size would actually mean that insects are going to have a bigger time preying on them, so this would strengthen if you interpret it like this