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  3. The cycle of fluctuation in snowshoe hare populations is unusual among animal species in that it is remarkably regular—peaking e

The cycle of fluctuation in snowshoe hare populations is unusual among animal species in that it is remarkably regular—peaking e

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问题     The cycle of fluctuation in snowshoe hare populations is unusual among animal species in that it is remarkably regular—peaking every eight to eleven years—and broadly synchronized over a vast area. Declines from peak levels are initiated by markedly lower overwinter survival of young hares, sharp decreases in birth rates, and a declining survival rate for adult hares. The onset of population increases is brought about by greatly improved rates of survival and birth.
    Some biologists hypothesize that the cycle begins when peak snowshoe hare populations exceed their winter food supply; resulting malnutrition triggers a population decline. As hare numbers fall, the ratio of predators to hares increases, as does the impact of predation on the hare population. This extends the decline beyond the period of winter food shortage. Hare scarcity then causes predator population declines, and with fewer predators and more abundant winter food, the hare population begins another cyclic increase. The high mobility of predators responding to local differences in hare abundance contributes to interregional synchrony.
According to the passage, biologists have suggested which of the following about snowshoe hare population fluctuations?
选项 A、Their regularity is due to the persistent threat of malnourishment that young hares face.
B、They are similar in length to those of other species of hare.
C、Their synchrony can be partly explained by the ability of predators to change the areas in which they hunt.
D、Their variation from region to region is partly due to regional differences in the availability of alternate prey for predator.
E、Their regularity is due to the constant availability of the food sources hares rely on.
答案C
解析 C正确，对应最后一句。
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