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  3. The cycle of fluctuation in snowshoe hare populations is unusual among anima

The cycle of fluctuation in snowshoe hare populations is unusual among anima

游客2024-01-10  51
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. [br] The passage suggests that which of the following is true of fluctuations in snowshoe hare populations?
选项 A、Changes in hare population levels are not highly correlated with changes in predator population levels.
B、Hare populations in one region are unlikely to peak at the same time that populations in nearby regions are at the lowest point of the cycle.
C、The regularity of hare population fluctuations is greater in regions where populations peak every eight years than in regions where they peak every eleven years.
D、In areas where hare population cycles are greater than eleven years, predator mobility is unusually high.
E、Fluctuations in hare populations vary greatly from region to region, depending on available winter food supply.
答案 B
解析 一个区域在最下面，这个区域就不可能在最上面，这就是区域间的同步，选项B正确。
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