The prairie vole, a small North American grassland rodent, breeds year-round, and a group of voles living together consists primarily of an extended family, often including two or more litters. Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups. The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.
Which of the following, if true, provides the strongest support for the explanation offered?
a. it is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.
b. prairie vole populations vary dramatically in size from year to year
c. the prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.
d. winters in the prarie voles' habitat are often harsh, with temperatures that drop well below freezing.
e. snakes, a major predator of young prarie voles, are active only from spring through early autumn.
answer is e. why not d?
prairie vole
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- ssmiles08
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I think you are missing the question. You have the stimulus and answer choices, but not the question.
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D) has no effect on the argument. winters are harsh, but it doesn't give it a reason for staying in extended families. The reason for staying in an extended group must have some connection to the mortality rate. Harsh winter doesn't mean that they decrease in mortality.sk8ternite wrote:The prairie vole, a small North American grassland rodent, breeds year-round, and a group of voles living together consists primarily of an extended family, often including two or more litters. Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups. The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.
Which of the following, if true, provides the strongest support for the explanation offered?
a. it is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.
b. prairie vole populations vary dramatically in size from year to year
c. the prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.
d. winters in the prarie voles' habitat are often harsh, with temperatures that drop well below freezing.
e. snakes, a major predator of young prarie voles, are active only from spring through early autumn.
answer is e. why not d?
Also, this answer choice can be seen as a weakener b/c they say that prairies live in large groups in the winter, which means they probably increase in size during the winter.
E) tells us that prairies are a targeted source for snakes, which is believable to cause a decline in the mortality rates. And since they snakes are the highest in spring through early autum...it explains why there is a decrease in group size during that season.
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Premise: Voles commonly live in large groups from late autumn through winter. But from spring through early autumn the group is far smaller.
Conclusion: Seasonal variation in-group size of voles living together can probably be explained by a seasonal variation in mortality among young voles
Now you have to look for an answer choice that strengthens the conclusion.
D) snakes, a major predator of young prairie voles, are active only from spring through early autumn.
i.e., snakes in early autumn are responsible for higher mortality rates among young voles. Correct ans D
Conclusion: Seasonal variation in-group size of voles living together can probably be explained by a seasonal variation in mortality among young voles
Now you have to look for an answer choice that strengthens the conclusion.
D) snakes, a major predator of young prairie voles, are active only from spring through early autumn.
i.e., snakes in early autumn are responsible for higher mortality rates among young voles. Correct ans D
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I believe you meant to say option "E" (and not "D").StrawberryCow wrote: D) snakes, a major predator of young prairie voles, are active only from spring through early autumn.
i.e., snakes in early autumn are responsible for higher mortality rates among young voles. Correct ans D
Argument has the following components:
Late autumn through winter: Large groups of voles
Spring through early autumn: Smaller groups
Then it conludes: The seasonal variation in groups size can probably be explained by a seasonal variation in mortality among young voles.
So, to strengthen this, we have to look for an answer choice that explains and coincides with the seasonal variation in mortality among young voles. Choice E clearly establishes this, because it says that Snakes, a major predator of young prairie voles, are active only from spring thru early autumn.
If that's the case, then there is a reason to believe that Snakes eat up voles from spring through autumn and hence, there are "smaller groups" of voles from spring through autumn.
D in fact, suggests the "other way round". If winters in vole's habitat are often harsh, and assuming that voles cannot withstand this harsh winter, then actually voles population should be "smaller" in winters; but the premise actually says that voles live in "large groups" in winter. So, D cannot be the answer.
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I'm not clear on why the group size decreases in spring and how it is connected to snakes in spring. A group size reduction can happen when a group of 10 splits into 2 groups of five. A snake in this scenario would make no difference. Please explain.
- DavidG@VeritasPrep
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You're right that there are many reasons why the group size of a given animal may become smaller. But according the argument, the reason that the vole group size is getting smaller is that the young are dying off at a greater rate. Because we're attempting to strengthen the argument, we want an answer choice that will support the notion that this increased mortality rate is what's causing the group size to shrink, not some other cause. If snakes eat young voles, and they're active at the time when the group is shrinking, that's a pretty good strengthener for the contention that it's the death of young voles that's causing the group to shrink, and not some unrelated cause that we haven't considered.TheGraduate wrote:I'm not clear on why the group size decreases in spring and how it is connected to snakes in spring. A group size reduction can happen when a group of 10 splits into 2 groups of five. A snake in this scenario would make no difference. Please explain.