PT153 S3 Q14 ExplanationGuam has 40 times more spiders

Answer choices, explained

1. A

   Correct58% picked this

   Birds compete with spiders for insect

   Why this is right

   This adds yet another reason why the presence of birds could suppress spider populations and why the absence of birds could allow the spider population to grow. Since they're competing for the same food supply, when birds are out of the picture, there's more food for spiders, so the islands insect population (the prey) can support a larger predator population (the spiders). Given that birds and spiders are limited by the same resource, it helps the plausibility of the "lack of birds enable lots of spiders" explanation.

   Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.

   58%
2. B

   No Impact5% picked this

   The biologists counted spiderwebs as a means of estimating the

   We don't have any idea whether counting spiderwebs is or isn't a reliable method of ascertaining the spider population, so we can't judge this answer's impact. Even if we conceded that counting spiderwebs is a good way to judge the spider population's size, this would only help us better trust the premise that there are 40 times more spiders. It wouldn't have anything to do with the conclusion, which is about why we have more spiders.

   5%
3. C

   No Impact21% picked this

   Spiderwebs are more prevalent on Guam than on

   This doesn't get at what's causing there to be lots of spiders; it's just presenting a fact that is consistent with the already established fact that Guam has 40 times as many spiders as do any nearby islands. Of course spiderwebs are more prevalent. There are 40 times as many spiders. I bet there's more spider poop too. This is telling us something we would have already known from common sense. It isn't helping us ascertain anything about the cause of this giant population of spiders, webs, poops.

   21%
4. D

   Weakens, if anything7% picked this

   The two bird species remaining on Guam have proliferated since the arrival of the

   If it turned out that the remaining two bird populations had greatly increased, now that all the other birds were dead, that would undermine the plausibility of the author's story. She is thinking that there are fewer birds than before, thus more spiders than before. All we know is that there are fewer bird species than before, but it's possible the 2 remaining ones have proliferated enough that the overall number of birds is still comparable. So the more birds we think there are, the more we'd be weakening the argument.

   7%
5. E

   No Impact9% picked this

   Brown tree snakes have proven difficult to eradicate

   We don't care whether the brown tree snakes still exist, are extinct, are easy to kill, are hard to kill. All that logically matters is that 10 of 12 bird species are now gone, and we're trying to assess the author's claim that the disappearance of these 10 bird species is the reason there are now so many spiders.

   9%