极地【威学教育】王鑫托福阅读TPO27-3阅读文本

2021年1月15日发(作者：连战)
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【王鑫托福阅读】托福TPO全集之TPO27-3


TPO27
TPO27-3 Predator Prey Cycles
1. In paragraph 1, why does the author discuss the moose and wolves on
Isle Royale?
A To provide an example of predators moving to new habitats by following
migrating prey B To show that the interactions between predator populations
and prey populations are not always might be expected
C To suggest that prey populations are more influenced by predation than
food availability and disease
D To argue that studies of geographically isolated populations tend not
to be useful to naturalists
2. The word “rebound” in the passage is closest in meaning to A escape
B recover C survive D resist
3. Paragraph 2 implies which of the following about experimental environments
in which predators become extinct?
A They may yield results that do not accurate predict changes of populations
in the wild.
B In these environments, the prey species is better adapted than the predator
species.
C These environments are appropriate only for studying small populations
of predators and prey.

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D They are unrealistic because some predators are also the prey of other
predators.
4. Which of the following can be inferred from paragraphs 2 and 3 about
the small mammals that experience population cycles? A Their population cycles
are not affected by predators.
B Their predators' populations periodically disappear.
C They typically undergo ten-year cycles.
D They have access to places safe from predators.
How do predators affect populations of the prey animals? The answer is
not as simple as might be thought. Moose reached Isle Royale in Lake Superior
by crossing over winter ice and multiplied freely there in isolation without
predators. When wolves later reached the island, naturalists widely assumed
that the wolves would play a key role in controlling the moose population.
Careful studies have demonstrated, however, that this is not the case. The
wolves eat mostly old or diseased animals that would not survive long anyway.
In general, the moose population is controlled by food availability, disease
and other factors rather than by wolves.
When experimental populations are set up under simple laboratory conditions,
the predator often exterminates its prey and then becomes extinct itself,
having nothing left to eat. However, if safe areas like those prey animals
have in the wild are provided, the prey population drops to low level but not
extinction. Low prey population levels then provide inadequate food for the
predators, causing the predator population to decrease. When this occurs, the
prey population can rebound. In this situation the predator and prey population
may continue in this cyclical pattern for some time.
Population cycles are characteristic of small mammals, and they sometimes
appear to be brought about by predators. Ecologists studying hare populations
have found that the North American snow shoe hare follows a roughly ten-year
cycle. Its numbers fall tenfold to thirty in a typical cycle, and a hundredfold
change can occur. Two factors appear to be generating the cycle: food plants
and predators.

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5. The word “roughly” in the passage is closest in meaning to
A usually B repeating C approximately D observable
6. The word “generating” in the passage is closest in meaning to
A producing B changing C speeding up D smoothing out
7. to paragraph 4, all of the following are true of the food of snowshoe
hares EXCEPT A The preferred food fore hares consists of willow and birch twigs.
B High fiber food is the most nutritious for hares.
C Depletion of the supply of willow and birch twigs cause low birth and
growth rates.
D The food supply takes two or three years to recover
8. The word “conjunction” in the passage is closest in meaning to A
determination
B combination C alternation D transformation
9. According to paragraph 5, which of the following statements best
characterizes the abundance cycle of the Canada lynx?
A It closely follows the cycle the snowshoe hare.
B When the numbers of lynx fall, the numbers of snowshoe hares soon decrease.
The preferred foods of snowshoe hares are willow and birch twigs. As hare
density increases, the quantity of these twigs decreases, forcing the hares
to feed on low- quality high-fiber food. Lower birth rates, low juvenile
survivorship, and low growth rates follow, so there is a corresponding decline
in hare abundance. Once the hare population has declined, it takes two to three
year for the quantity of twigs to recover.