PrepTest 141, Section 4, Question 15
Hine's emerald dragonflies are an endangered species that(52 more words not shown)
Which one of the following,(9 more words not shown)
- ARed devil crayfish(14 more words not shown)
- BRed devil crayfish(8 more words not shown)
- CThe varied diet(16 more words not shown)
- DRed devil crayfish(11 more words not shown)
- EPopulations of red(19 more words not shown)
Reading the argument
Why would dragonflies do better around an animal that eats their larvae?
My first guess is that the crayfish keep something worse away. Suppose minnows eat enormous numbers of the larvae, and the crayfish eat those minnows. The crayfish could eat some larvae themselves while still giving the dragonflies a net benefit by removing a more dangerous predator.
That's one possible explanation, not a fact we've been told. There could also be an environmental advantage: perhaps crayfish occur in especially favorable water conditions, and that benefit outweighs the losses from predation. The important thing is to find a reason dragonflies fare better where crayfish are present.
What we’re looking for
The question asks us to explain both facts together. We should accept that the crayfish eat larvae and that the dragonfly population is more likely to stay healthy around them. An answer needs an offsetting benefit or some other difference that makes those facts fit.
Working the answers
- ACorrect
The chambers offer a different benefit from my predator prediction: water that remains when the surrounding wetland dries out. The passage says the larvae can survive only in water. These pockets could therefore give them somewhere to survive a dry period when larvae elsewhere would lose the water they need. The crayfish can still eat some larvae while also creating habitat that helps the population survive.
- B
Not harming the adults doesn't explain a benefit to the population. We already know the crayfish threaten the larvae. Saying one life stage is safe leaves us asking why dragonflies do better with this additional predator than without it.
- C
This is the opposite of the first prediction. If the crayfish don't eat any animals that prey on the larvae, their diet doesn't supply the hoped-for protection from worse predators. The mention of predators is tempting, but the actual claim removes that explanation instead of providing it.
- D
How widely crayfish are distributed doesn't tell us why dragonfly populations remain healthier in the places where the two coexist. The crayfish could live in many places without benefiting dragonflies in any of them. We need a relevant feature of their presence, not a count of their locations.
- E
This tells us that crayfish populations can remain stable after the local dragonflies disappear. It concerns how dependent the crayfish are on the dragonflies, not how the dragonflies benefit from the crayfish. It supplies no explanation for the healthier dragonfly populations.
More Paradox questions
Learn the LSAT our way
Our platform drills Paradox questions at your level and adjusts as you improve.