#14 - Guam has 40 times more spiders than nearby islands

[KelseyWoods]

Strengthen-CE. The correct answer choice is (A)

The biologists make a causal conclusion here, arguing that the cause is the loss of bird species and the effect is the increase in the spider population. That's the relationship we're trying to strengthen. The conclusion is based on the premise that the birds prey on spiders and use spiderwebs for their nests. So, basically, with fewer birds, there are fewer predators eating spiders and destroying their homes.

When you have a causal argument in a strengthen question, your prephrase is essentially that you are looking for one of the 5 ways to strengthen a causal conclusion (in this case, that fewer birds are causing more spiders): eliminate an alternate cause; show that when you have the cause, you have the effect; show that when you don't have the cause, you don't have the effect; eliminate the possibility of the reverse cause and effect; or support the data.

Answer choice (A): This is the correct answer. If birds compete with spiders for insect prey, that's another reason why their presence might keep the spider population down--they're competing for the same food source. So not only do birds eat spiders and destroy their homes, they also eat the things spiders would eat. This is a "support the data" method of strengthening a causal conclusion. It supports the stimulus data by providing another way in which birds may directly keep the spider population down, which strengthens the conclusion that fewer birds would allow the spider population to increase.

Answer choice (B): How the biologists estimated the spider population has nothing to do with whether the loss of bird species is responsible for the increase in the spider population.

Answer choice (C): Comparing the number of spiderwebs on Guam to nearby islands it not relevant to our causal relationship about birds and spiders. We know there's an increase in the spider population on Guam. We want to strengthen the idea that the loss of bird species is the cause.

Answer choice (D): The proliferation of a couple of bird species since the arrival of brown tree snakes has nothing to do with whether the loss of bird species is responsible for the increase in the spider population.

Answer choice (E): The eradication of brown tree snakes have nothing to do with our birds and spiders.

[Jordannt]

I pretty much guessed on this question but in looking over the answer choices I am struggling to figure out why A is the correct answer.

[Jordannt]

I pretty much guessed on this question but in looking over the answer choices I am struggling to figure out why A is the correct answer.

think i figured it out...is this answer choice based on the statement that the increase of spider population let to the decrease of bird population ... ugh after staring at item pretty sure that is it

[Jeremy Press]

Hi Jordan,

You're on the right track, though I would've stated it in the reverse: the author is arguing that the island's loss of bird species (which was caused by introduction of snakes) led to an increase in the island's spider population. One of the ways the argument mentions this happened is because birds were a menace to spiders (preying on them, destroying their nests), so when birds went away, spider populations naturally increased. Answer choice A gives another reason the loss of birds led to increase of spiders: when the birds went away, the spiders had less competition for the insects they eat.

I hope this helps!

Jeremy

[thedramallama]

Is this the right reasoning for AC C?

The presence of more spiderwebs on Guam than other islands only affirms the fact that Guam has more spiders. Of course if there are more spiders on Guam, we would see more webs. AC C does nothing to explain the reasoning behind why the decrease in the bird population caused an increase in the spider population.

Thank you!

[Adam Tyson]

Correct, thedramallama! That's exactly what's happening with answer C. It's a trap answer for folks who are focused on the wrong thing, and see it as a way of strengthening the claim that there are more spiders on Guam than on nearby islands. As you've pointed out, that's not what the biologists concluded, and so is the wrong focus for this question. Well done!

[lsatbossintraining]

Hi -

I don't understand. How does the fact that spiders and birds compete for prey strengthen the idea that the decrease in species of birds increased the number of spiders? Is there something obvious about the stimulus that should direct us to (A), or is this one of those questions that requires us to be nimble.

This is a really tough one, so a step-by-step breakdown of each answer choice would be greatly appreciated. Spent too much time on this question.

Also, is there a strategy to guessing? Really didn't know what to do here.

Many thanks,
Kyle

[KelseyWoods]

Hi Kyle!

Here's a question breakdown for you:

Strengthen-CE. The correct answer choice is (A)

The biologists make a causal conclusion here, arguing that the cause is the loss of bird species and the effect is the increase in the spider population. That's the relationship we're trying to strengthen. The conclusion is based on the premise that the birds prey on spiders and use spiderwebs for their nests. So, basically, with fewer birds, there are fewer predators eating spiders and destroying their homes.

When you have a causal argument in a strengthen question, your prephrase is essentially that you are looking for one of the 5 ways to strengthen a causal conclusion (in this case, that fewer birds are causing more spiders): eliminate an alternate cause; show that when you have the cause, you have the effect; show that when you don't have the cause, you don't have the effect; eliminate the possibility of the reverse cause and effect; or support the data.

Answer choice (A): This is the correct answer. If birds compete with spiders for insect prey, that's another reason why their presence might keep the spider population down--they're competing for the same food source. So not only do birds eat spiders and destroy their homes, they also eat the things spiders would eat. This is a "support the data" method of strengthening a causal conclusion. It supports the stimulus data by providing another way in which birds may directly keep the spider population down, which strengthens the conclusion that fewer birds would allow the spider population to increase.

Answer choice (B): How the biologists estimated the spider population has nothing to do with whether the loss of bird species is responsible for the increase in the spider population.

Answer choice (C): Comparing the number of spiderwebs on Guam to nearby islands it not relevant to our causal relationship about birds and spiders. We know there's an increase in the spider population on Guam. We want to strengthen the idea that the loss of bird species is the cause.

Answer choice (D): The proliferation of a couple of bird species since the arrival of brown tree snakes has nothing to do with whether the loss of bird species is responsible for the increase in the spider population.

Answer choice (E): The eradication of brown tree snakes have nothing to do with our birds and spiders.

Note: this explanation has been copied into the first post above.

Hope this helps!

Best,
Kelsey

[lsatbossintraining]

Much appreciated as always Kelsey.

When strengthening cause and effect arguments, are the methods you suggested bulletproof? Should they always lead me to the write answer choice?

Thanks much.

Kyle

[Dave Killoran]

Hi Kyle,

They are bulletproof in the sense that if you find one it will lead to the correct answer (and these are covered in detail in our courses and books, so grab those if you haven't yet). However, could they do something else? Yes. It doesn't happen often but the world of logic is big and there are always exceptions. It's not all that common though!

Thanks!