PrepTest 124, Section 1, Question 9
Global surveys estimate the earth's population of nesting(42 more words not shown)
Which one of the following(7 more words not shown)
- AThe decline in(20 more words not shown)
- BIf the global(20 more words not shown)
- CThe global population(12 more words not shown)
- DVery few leatherback(4 more words not shown)
- EThe only way(17 more words not shown)
Reading the argument
We counted nesting females. The conclusion is about the entire species.
A drop of more than two-thirds among nesting female turtles sounds concerning. But the rule we are given concerns a species whose overall population has fallen that much. Those aren't automatically the same measurement. The number of nesting females could change without every other part of the population changing at the same rate.
The fact that these females lay eggs makes their decline seem especially troubling, but that isn't the argument's stated route to the conclusion. The argument applies a rule about the whole population using a figure for one part of it. To make that move, it treats the nesting females as an indicator of the population as a whole.
What we’re looking for
For the necessary-assumption question, that's the connection I want: the decline among nesting females must reflect the decline in the overall leatherback population.
Working the answers
- ACorrect
This supplies the link between the group surveyed and the whole species. If the nesting-female decline is proportional to the overall decline, the survey can serve as the population measure the argument needs.
Without that link, the nesting-female count could fall sharply while the overall population changed very differently. The argument would then have no basis for applying its rule about a species-wide decline of more than two-thirds. A identifies the representative relationship the argument relies on.
- B
The conclusion is that the species is in danger now, based on the past 15 years. B concerns another decline over the next 15 years and says extinction will eventually occur. The argument doesn't need either that future prediction or the stronger claim of eventual extinction. Being at risk isn't the same as being certain to disappear.
- C
The sexes don't have to be equally numerous for nesting females to be a useful indicator. Imagine the ratio were unequal but remained stable as the population declined. The relevant question is whether the nesting-female decline tracks the overall decline, not whether half of all turtles are male and half female.
- D
The argument doesn't require a particular number of captive turtles. It requires a connection between the surveyed nesting females and the species-wide population trend. Knowing that few turtles are in captivity wouldn't by itself establish that connection, and the argument doesn't separately restrict its conclusion to turtles in the wild.
- E
This proposes a particular way to protect the turtles. We aren't deciding how to save them; we're deciding whether the argument supports saying they are in danger. Habitat restoration might help, or some other intervention might help. The argument doesn't depend on captive breeding being the only solution.
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