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  3. For most species of animals, the number of individuals in the species is inversely proportional to the average body size for mem

For most species of animals, the number of individuals in the species is inversely proportional to the average body size for mem

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问题 For most species of animals, the number of individuals in the species is inversely proportional to the average body size for members of the species: the smaller the body size, the larger the number of individual animals. The tamarin, a small South American monkey, breaks this rule. Of the ten primate species studied in Peru’s Manu National Park, for example, the two species of tamarins, saddle-backed and emperor, are the eighth and ninth least abundant, respectively. Only the pygmy marmoset, which is even smaller, is less abundant. The tamarin’s scarcity is not easily explained; it cannot be dismissed as a consequence of diet, because tamarins feed on the same mixture of fruit, nectar, and small prey as do several of their more numerous larger counterparts, including the two capuchins known as the squirrel monkey and the night monkey. Although the relative proportions of fruits consumed varies somewhat among species, it is hard to imagine that such subtle differences are crucial to understanding the relative rarity of tamarins.
To emphasize just how anomalously rare tamarins are, we can compare them to the other omnivorous primates in the community. In terms of numbers of individuals per square kilometer, they rank well below the two capuchins, the squirrel monkey and the night monkey. And in terms of biomass, or the total weight of the individuals that occupy a unit area of habitat, each tamarin species is present at only one-twentieth the mass of brown capuchins or one-tenth that of squirrel monkeys. To gain another perspective, consider the spatial requirements of tamarins. Tamarins are rigidly territorial, vigorously expelling any intruders that may stray within the sharply defined boundaries of their domains. Groups invest an appreciable part of their time and energy in patrolling their territorial boundaries, announcing their presence to their neighbors with shrill, sweeping cries. Such concerted territoriality is rather exceptional among primates, though the gibbons and siamangs of Asia show it, as do a few other New World species such as the titi and night monkeys. What is most surprising about tamarin territories is their size.
Titi monkeys routinely live within territories of 6 to 8 hectares, and night monkeys seldom defend more than 10 hectares, but tamarin groups routinely occupy areas of 30 to 120 hectares. Contrast this with the 1 to 2 hectares needed by the common North American gray squirrel, a nonterritorial mammal of about the same size. A group of tamarins uses about as much space as a troop of brown capuchins, though the latter weighs 15 times as much. Thus, in addition to being rare, tamarins require an amount of space that seems completely out of proportion to their size.
The primary concern of the passage is to
选项 A、recommend a policy
B、evaluate a theory
C、describe an unusual condition
D、explain the development of a hypothesis
E、support one of several competing hypotheses
答案C
解析 Main idea
Answering this question requires identifying an abstract description of the primary purpose of the passage. The passage focuses in different ways on an unusual condition, namely, the anomalous relationship between tamarins’ relatively small average body size and the number of individuals in the species.
A The passage is not concerned with recommending any policy.
B The passage does not focus on any theory; it considers a phenomenon, but proposes no theory to explain that phenomenon.
C Correct. The passage’s primary concern is to describe an unusual phenomenon, namely, how tamarins "break the rule" that, in general, the number of individuals in a species is inversely proportional to the average body size of members of the species.
D The passage is primarily concerned with a particular, unusual phenomenon, but it offers no hypothesis regarding it, nor does it discuss the development of any such hypothesis.
E Although the passage gives passing consideration to some hypotheses, its primary concern is to note certain characteristics of tamarins. The passage does not primarily concern itself with any hypotheses.
The correct answer is C.
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