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#8- Delta green ground beetles sometimes remain motionless

Echx73
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Hello,

I am wondering why A is the best answer? I crossed it off because since 85 was a wetter year there should be more movement of the beetles compared to a relatively dry year such as 89. Intuitively, this would suggest in my mind that the wetter the season the more you will see the beetle. Therefore, 85 would have more beetles than 89 which is not the case so I crossed A off. Also, can you tell me why B is incorrect? C, D and E are pretty self explanatory of why they are wrong.

Thanks!
Eric
Adam Tyson
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I think you may have answered your own question without realizing it, Eric! Your analysis of A is perfect - 85 was wetter, so the beetles were probably moving more and thus easier to spot. That explains why the observer saw so many more in that year than in 89, when they would have been moving less if at all. It looks like maybe you mis-read the stimulus, thinking the opposite occurred, that more were seen in 89 than in 85? Check it again and you will see the reverse is the case - in 85 it was 38 in 2 hours, in 89 it was only 10 in 9 hours.

So why does that make A the right answer? Focus on the conclusion - what is this author trying to prove? It's the beginning of the last sentence of the stimulus - "This difference probably does not reflect a drop in the population of these rare beetles over this period". In other words, he is saying that a drop in the population is likely NOT the reason for the lower number in 89. Per the stem, we want to strengthen that claim, and A does it by giving another explanation (an alternate cause, perhaps?) for the lower number - not that there were fewer beetles, but that there was less movement and thus they weren't as easily spotted.

B is incorrect because it does nothing to help that conclusion, that a drop in population is not the reason for the lower numbers seen in 89. B might actually weaken the argument by suggesting that in 89 the beetle habitat was reduced in size, thus reducing the population (the very thing we want to say did NOT happen). I'm more inclined to say that B simply has no impact - my reaction to it is "so what?" It tells us where their habitat is, but tells us nothing about whether this particular area is such a habitat and nothing about why, other than a population decrease, we saw fewer beetles in 89 than in 85.

Good work! Now just tie your analysis of the answer back to your goal, helping make the conclusion better, and you are home free.
Adam M. Tyson
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Joel T
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Hello,

I am having trouble understanding this one.

I chose E because I thought it eliminated an alternative possible explanation for why the beetle count was lower in 89 versus 85.

I know the stimulus explains that there was a drop because it was drier, but doesn't "no predators relies on delta green ground beetle for a major portion of its food supply" also eliminate that another alternative explanation?

Thanks for your help.
Zach Foreman
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Although this is a strengthen question, we can use the Assumption Negation Technique to help us eliminate wrong answers. Why? Well, because an assumption does strengthen a conclusion and if we negate it and the conclusion is unaffected, then it isn't really relevant.
Let's start with the correct answer, A. What if the beetles were easily seen even when not moving? Wouldn't that totally undermine the argument? Then it wouldn't matter if it were wet or dry or if the beetles were active or inactive, the counter could just count them when stationary. So, we can see that assuming that they are difficult to see when stationary is an important fact and does strengthen the argument.
What about E? What if lots of predators relied on the beetles for food? Well, what difference would that make if we don't know whether there were more or less predators in 1989 vs 1985? The mere presence of predators wouldn't seem to make a difference. Therefore, it is irrelevant.
Now, if the answer had said "No new predator species invaded the territory since 1986" then that would eliminate an alternative cause.
Remember, you need a difference to explain a difference.

Difficulty in counting stationary beetles :arrow: Fewer beetles counted in 1989
The alternate cause being explicitly denied is population decline of beetles :arrow: Fewer beetles counted in 1989

What else was different between 1985 and 1989? We don't know. If another answer denied any other difference, it would be a correct answer. "There were no more predators counted in 1989 than 1985." or "1989 was not much colder/hotter than 1985." or "The habitat of the beetle did not shrank considerably in 1989." Any of these would eliminate an alternate cause. E suggests an alternate cause but because it doesn't say anything about a difference between 1989 and 1985 doesn't quite go far enough in eliminating an alternate cause.