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One explanation for the tendency of animals to be more vigilant in smaller groups than in larger ones assumes that the vigilant behavior—looking up, for example—is aimed at predators. If individuals on the edge of a group are more vigilant because they are at greater risk of being captured, then individuals on average would have to be more vigilant in smaller groups, because the animals on the periphery of a group form a greater proportion of the whole group as the size of the group diminishes.
However, a different explanation is necessary in cases where the vigilant behavior is not directed at predators. J. Krebs has discovered that great blue herons look up more often when in smaller flocks than when in larger ones, solely as a consequence of poor feeding conditions. Krebs hypothesizes that the herons in smaller flocks are watching for herons that they might follow to better feeding pools, which usually attract larger numbers of the birds.
[阅读&逻辑 ]经典真题320篇 -9340
The highlighted sentence serves primarily to
[阅读&逻辑 ]经典真题320篇 -9339
The author would most likely agree with which of the following assertions about the environmental impact of hydroelectric power plants?
[阅读&逻辑 ]经典真题320篇 -9338
The passage suggests that which of the following contributed to the erosion after the First World War of the progress previously realized by the labor movement in the United States?
[阅读&逻辑 ]经典真题320篇 -9337
According to the passage, which of the following statements about the National War Labor Board is true?
[阅读&逻辑 ]经典真题320篇 -9336
It can be inferred from the passage that which of the following was one of Local 36’s grievances against the Little Rock laundry owners?
[阅读&逻辑 ]经典真题320篇 -9335
The passage is primarily concerned with discussing
[阅读&逻辑 ]经典真题320篇 -9334
According to the passage, Appalachian square dancing differs from English country dancing in that Appalachian square dancing
[阅读&逻辑 ]经典真题320篇 -9333
The passage suggests that which of the following was true of
[阅读&逻辑 ]经典真题320篇 -9332
The statements given are structured to lead to which of the following conclusions?
[阅读&逻辑 ]经典真题320篇 -9331
Consider each of the choices separately and select all that apply. It can be inferred that historical demographers generally believe which of the following about communities of fewer than 10,000 people in early-modern Germany?
[阅读&逻辑 ]经典真题320篇 -9330
The author suggests that according to historical demographers, the birth rate in early-modem German cities
[阅读&逻辑 ]经典真题320篇 -9329
Which of the following most logically completes the argument?
[阅读&逻辑 ]经典真题320篇 -9328
The highlighted portion of the passage serves primarily to
[阅读&逻辑 ]经典真题320篇 -9327
According to the passage, certain African literatures have
[阅读&逻辑 ]经典真题320篇 -9326
It can be inferred from the passage that the Tea Cess Committee reorganized as the Indian Tea Market Expansion Board in order to
[阅读&逻辑 ]经典真题320篇 -9325
The passage suggests that "small packets of leaf fragments" were
[阅读&逻辑 ]经典真题320篇 -9324
In the argument in the editorial, the part that is highlighted plays which of the following roles?
[阅读&逻辑 ]经典真题320篇 -9323
Consider each of the choices separately and select all that apply.Which of the following can be inferred from the passage about the"period of relative warmth"
[阅读&逻辑 ]经典真题320篇 -9322
Which of the following best describes the organization of the passage?
[阅读&逻辑 ]经典真题320篇 -9321
It can be inferred that the author would agree with which of the following statements about glaciers?