SAT阅读模拟题之number fluctuations of animals.

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　　 Although numbers of animals in a given region may

　　 fluctuate from year to year, the fluctuations are often

　　 temporary and, over long periods, trivial. Scientists

　　 have advanced three theories of population control to

　　(5) account for this relative constancy.

　　 The first theory attributes a relatively constant popu-

　　 lation to periodic climatic catastrophes that decimate

　　 populations with such frequency as to prevent them

　　 from exceeding some particular limit. In the case of

　　(10) small organisms with short life cycles, climatic changes

　　 need not be catastrophic: normal seasonal changes in

　　 photoperiod (daily amount of sunlight), for example,

　　 can govern population growth. This theory---the

　　 density-independent view---asserts that climatic factors

　　(15) exert the same regulatory fect on population regard-

　　 less of the number of individuals in a region.

　　 A second theory argues that population growth is

　　 primarily density-dependent---that is, the rate of

　　 growth of a population in a region decreases as the

　　(20) number of animals increases. The mechanisms that

　　 manage regulation may vary. For example, as numbers

　　 increase, the food supply would probably diminish,

　　 which would increase mortality. In addition, as Lotka

　　 and Volterra have shown, predators can find prey more

　　(25) easily in high-density populations. Other regulators

　　 include physiological control mechanisms: for example.

　　 Christian and Davis have demonstrated how the

　　 crowding that results from a rise in numbers may bring

　　about hormonal changes in the pituitary and adrenal

　　(30) glands that in turn may regulate population by lowering

　　 sexual activity and inhibiting sexual maturation. There

　　 is evidence that these fects may persist for three

　　 generations in the absence of the original provocation.

　　 One challenge for density-dependent theorists is to

　　(35) develop models that would allow the precise prediction

　　 of the fects of crowding.

　　 A third theory, proposed by Wynne-Edwards and

　　 termed “epidtic,” argues that organisms have evolved

　　 a “code”in the form of social or epidtic behavior

　　(40) displays, such as winter-roosting aggregations or group

　　 vocalizing; such codes provide organisms with infor-

　　 mation on population size in a region so that they can,

　　 if necessary, exercise reproductive restraint. However,

　　 wynne-Edwards’ theory, linking animal social behavior

　　(45) and population control, has been challenged, with some

　　 justification, by several studies.

　　1. The primary purpose of the passage is to

　　(A) argue against those scientists who maintain that animal populations tend to fluctuate

　　(B) compare and contrast the density-dependent and epidtic theories of population control

　　(C) provide example of some of the ways in which animals exercise reproductive restraint to control their own numbers

　　(D) suggests that theories of population control that concentrate on the social behavior of animals are more open to debate than are theories that do not

　　(E) summarize a number of scientific theories that attempt to explain why animal populations do not exceed certain limits

　　2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to

　　(A) use their theory to explain the population growth of organisms with short life cycles

　　(B) reproduce the results of the study of Christian and Davis

　　(C) explain adequately why the numbers of a population can increase as the population’s rate of growth decreases

　　(D) make sufficiently accurate predictions about the fects of crowding

　　(E) demonstrate how predator populations are themselves regulated

　　3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

　　(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.

　　(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease.

　　(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase.

　　(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.

　　(E) After the number of eagles in Montana decreases, the food supply of this population of eagles also begins to decrease.

　　4. According to the Wynne-Edwards theory as it is described in the passage, epidtic behavior displays serve the function of

　　(A) determining roosting aggregations

　　(B) locating food

　　(C) attracting predators

　　(D) regulating sexual activity

　　(E) triggering hormonal changes

　　5. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with

　　(A) complete indifference

　　(B) qualified acceptance

　　(C) skeptical amusement

　　(D) perplexed astonishment

　　(E) agitated dismay

　　6. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?

　　(A) Thus wynne-Edwards’ theory raises serious questions about the constancy of animal population in a region.

　　(B) Because Wynne-Edwards’ theory is able to explain more kinds of animal behavior than is the density-dependent theory, epidtic explanations of population regulation are now widely accepted.

　　(C) The results of one study, for instance, have suggested that group vocalizing is more often used to dend territory than to provide information about population density.

　　(D) Some of these studies have, in fact, worked out a systematic and complex code of social behavior that can regulate population size.

　　(E) One study, for example, has demonstrated that birds are more likely to use winter-roosting aggregations than group vocalizing in order to provide information on population size.

　　Correct Answers：EDADBC

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