LSAT 153 | Section 3 | Logical Reasoning: Q14

LR Question 14 Explanation

QUESTION TEXT: Guam has 40 times more spiders than nearby islands…

QUESTION TYPE: Strengthen

CONCLUSION: The introduction of the brown tree snake caused Guam to have 40 times more spiders than nearby islands.

REASONING: The brown tree snake introduced in Guam in 1940 eliminated ten of twelve native bird species by 1980. Many birds were natural predators of spiders.

ANALYSIS: To strengthen our argument, we want something that will highlight the impact that the birds had on spider populations. The greater the impact that birds have on keeping spider populations down, the more significant it is that these birds are now gone as a result of the introduction of the brown tree snake.

___________

1. CORRECT. If this is true, then birds were doing multiple things to keep spider populations down. Not only did they prey on spiders, but they also prevented spiders from having a larger food source by competing for insect prey. This would impact their ability to thrive in multiple ways and would further highlight the importance of birds on controlling spider populations.
2. How biologists estimate spider populations isn’t relevant to the cause of increasing spider populations.
3. More spiders would be the cause of more spiderwebs. But we are interested in the cause for having more spiders in the first place! This answer doesn’t tell us anything about that.
4. This weakens our argument. If the remaining bird species grew rapidly, then they would presumably be able to keep spider populations down by themselves. Therefore, the rise in spider populations would not be caused by the introduction of the brown tree snake which eliminated the other ten bird species.
5. The difficulty of removing brown tree snakes is the issue we are concerned with. This answer is simply irrelevant.

Recap: The question begins with “Guam has 40 times more spiders than nearby islands”. It is a Strengthen question. Learn more about LSAT Strengthen questions in our guide to LSAT Logical Reasoning question types.