Self-study
Guam has 40 times more spiders than nearby islands have. ██████████ █████ ████ ████ ██ █ ███████████ ██ ███ ██████████ █████ ████████████ ████ ████ ██ ███ █████ ████ ██████ █████ ██ ███ █████ ███ ██████████ ███ ██ ██████ ██████ ████ ████████ ███ ██████████ █████████ ███ ██████ ██████████████ ████████ ██ ███ ████ ██ ████ ████████ ███████ ████ █████ ████ ██ ███████ ███ ████ ███ ██████████ ██ ████████████ ██████
Summarize Argument: Phenomenon-Hypothesis
The biologists hypothesize that the spider population’s increase is a result of the introduction of the brown tree snake. This is based on the fact that the brown tree snake eliminated native bird species, and on the subsidiary conclusion that this loss of bird species caused the spider population to increase. This sub-conclusion is based on the fact that many birds prey on spiders and use spiderwebs to construct nests.
Notable Assumptions
The author assumes that there’s no other explanation for the increase in spider population on Guam besides the decrease in bird species. The author also assumes that there was a decrease in overall bird population (as opposed to simply a decrease in the number of species, which doesn’t automatically indicate a decrease in population).
14.
Which one of the following, ██ █████ ████ ███████████ ███ ███████████ ███████████
a
Birds compete with ███████ ███ ██████ █████
This strengthens by providing another causal mechanism that could show bird populations can affect spider populations. If birds and spiders compete for food, a decrease in birds would mean spiders have less competition for food. This could help spiders survive and thrive.
Causal mechanism
Causal mechanism
Answers that undermine, or help establish, the practical story of how an alleged cause could produce the alleged effect.
b
The biologists counted ██████████ ██ █ █████ ██ ██████████ ███ ██████ ███████████
This has no clear impact on the hypothesis. So, we estimated the spider population increase based on an increase in the number of spiderwebs. Does the spider population have anything to do with a decline in birds? (B) is silent on this.
c
Spiderwebs are more █████████ ██ ████ ████ ██ ██████ ████████
This doesn’t help connect the increase in spiders with the bird population decline. The issue is the cause of the spider population increase, not whether the spider population has increased. We already know Guam has more spiders than other nearby islands.
Irrelevant corroboration
Irrelevant corroboration
Answers that provide additional support for a claim that the argument doesn't need more support for.
d
The two bird ███████ █████████ ██ ████ ████ ████████████ █████ ███ ███████ ██ ███ █████ ████ ███████
This undermines the argument by pointing out that overall number of birds might have increased even if the number of species has gone down.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
e
Brown tree snakes ████ ██████ █████████ ██ █████████ ██ █████
This has nothing to do with whether the snakes caused the bird population to decline and whether the bird population decline caused an increase in spider population. We care about the effect of the snakes. Not how easy it is to remove the snakes.