broall wrote:
A fourteen-year study of finches on the Galapagos islands concluded that there is a definite relationship between climate and the population size of finch species that thrive at various times. During droughts, more members of large finch species survive because
their bills are large enough to crack large, hard seeds, giving them a food supply unavailable to smaller birds. In rainy years, fewer members of the large finch species survive because the additional moisture fosters the growth of plants that produce small seeds.
The larger finch varieties have to consume enormous numbers of small seeds to meet their energy demands, and some just cannot eat them fast enough.
Which one of the following must be assumed in order to justify the conclusion that climatic variations cause a major difference in survival rates of small and large finches?
(A) During drought conditions, the weather promotes the growth of plants that produce small, hard seeds.
(B) A lengthy period of rainy weather results in fewer large, hard seeds being produced.
(C) In rainy periods, the small finches gather enough food to grow much larger and heavier, but their ultimate size is limited by
their inability to eat small seeds fast.
(D) The Galapagos climate during this fourteen year period had about as much dry weather as it had wet weather.
(E) Small seeds do not have to be cracked open in order to be digested by any of the finch varieties.
Source: LSAT
The Argument
(During droughts finches survive because they can crack large, hard seeds & during rain, there is more plants that produce small seeds)
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There is a correlation between climate and population (aka, more rain causes less finches)
My Thoughts
This argument is saying that, just because there is more of one plant's seeds during rain, the finches are less likely to survive. Ummmmm what? This argument is kind of like the following: Subway chicken sandwiches are necessary for human survival. During the summer, we all eat lots of Subway chicken sandwich and everything is awesome and plenty of people make it through the summer. However, during the winter, Subway sells turkey sandwiches. Therefore, more people die. The assumption in these arguments is something like "when the rain produces these small seeds, there are less large, hard seeds." The argument is assuming that more of one thing means less of the other.
(A) Out of scope. All we need to know here is that during droughts there are enough hard seeds to go around for all the finches. It doesn't really matter what else there is because the finches are doing fine during droughts.
(B) Correct. If more rain = less large hard seeds, then we can clearly see how this would be detrimental to the finch's survival. If we negate this and say that "rainy weather does NOT result in fewer large, hard, seeds" then this would mean that there doesn't seem to be as much of a relationship between climate and survival as people think
(C) Out of scope. In the argument, we are talking about survival and not about size. This seems like a trap answer for someone that was running out of time and saw "population SIZE of finch species) and went with it.
(D) Not necessary. We don't need to assume that there was as much of one kind of weather as the other. We are talking about what happens during those kinds of weather. It doesn't matter if that type of weather is any more or less frequent then the other type.
(E) Out of scope. We don't care if the seeds have to or don't have to be cracked open. The seeds are important not because of their "crackability" but because of their type and how available they are to these finches. There does not seem to be any correlation between "crackability" and survival
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