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 account for this relative constancy.
The first theory attributes a relatively constant population to periodic climatic catastrophes that decimate populations with such frequency as to prevent them from exceeding some particular limit. In the case of 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 exert the same regulatory effect on population regardless 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 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 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 glands that in turn may regulate population by lowering sexual activity and inhibiting sexual maturation. There is evidence that these effects may persist for three generations in the absence of the original provocation. One challenge for density-dependent theorists is to develop models that would allow the precise prediction of the effects of crowding.
A third theory, proposed by Wynne-Edwards and termed “epideictic,” argues that organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint. However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies.
4.a According to the Wynne-Edwards theory as it is described in the passage, epideictic behavior displays serve the function of
(A) determining roosting aggregations
(B) locating food
(C) attracting predators
(D) regulating sexual activity（D）
(E) triggering hormonal changes
我选的是A，这是文中such as举例的内容，所以都没有看其他选项，D是根据文中推断出来的。可是题目没有什么明确的提示，我还是弄不明白，我觉得两个都可以的，请指教
GreenHorse，I know that "C" is correct,since I have found the key words "exercise reproductive restraint
".
Now,what I want to know is the reason why the answer "A" is wrong?
Could you give me some more advices?
Thanks a lot!
GreenHorse 同意解释。
但是不是social behavior，一个是epideictic behavior 的区别，而是 SUCH AS 和 SO THAT 的区别。
问题问的是 serve the function of 所以 这里应该找到SO THAT后的关键词
好像不是这么理解的. 文章明显提到"argues that organisms have evolved a "code" in the form of social or epideictic behavior displays, such as winter roosting aggregations or group vocalizing;" 所以这里social behavior和epideictic behavior是一样的.
A之所以错是因为问题问的不是epideictic behavior的形式, 而是animal 通过这种epideictic behavior能起到什么作用: exercise reproductive restraint(控制繁殖). 这点也是第三中理论的中心思想.
不过这题我也被表明现象迷惑了一下下, 选了A.
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