托福备考托福阅读34套TPO样题+解析+译文3--3 The Long-Term Stability

托福考试

复习

托福阅读TPO3(试题+答案+译文)第3篇:The Long-Term Stability of

Ecosystems

托福阅读原文

Plant communities assemble themselvesflexibly, and their particular

structure depends on the specific history of thearea. Ecologists use the

term “succession” to refer to the changes that happenin plant

communities and ecosystems over time. The first community in

asuccession is called a pioneer community, while the long-lived

community at theend of succession is called a climax community. Pioneer

and successional plantcommunities are said to change over periods from

1 to 500 years. Thesechanges—in plant numbers and the mix of species—are cumulative. Climaxcommunities themselves change but over periods

of time greater than about 500years.

An ecologist who studies a pond today maywell find it relatively

unchanged in a year’s time. Individual fish may bereplaced, but the

number of fish will tend to be the same from one year to thenext. We can

say that the properties of an ecosystem are more stable than

theindividual organisms that compose the ecosystem.

At one time, ecologists believed that speciesdiversity made ecosystems

stable. They believed that the greater the diversitythe more stable the

ecosystem. Support for this idea came from the observationthat long-lasting climax communities usually have more complex food webs

andmore species diversity than pioneer communities. Ecologists

concluded that theapparent stability of climax ecosystems depended on

their complexity. To takean extreme example, farmlands dominated by a

single crop are so unstable thatone year of bad weather or the invasion

of a single pest can destroy the entirecrop. In contrast, a complex climax

community, such as a temperate forest, willtolerate considerable damage

from weather to pests.

The question of ecosystem stability iscomplicated, however. The first

problem is that ecologists do not all agreewhat “stability” means.

Stability can be defined as simply lack of change. Inthat case, the climax

community would be considered the most stable, since, bydefinition, it

changes the least over time. Alternatively, stability can bedefined as the

speed with which an ecosystem returns to a particular formfollowing a

major disturbance, such as a fire. This kind of stability is alsocalled

resilience. In that case, climax communities would be the most fragileand

the least stable, since they can require hundreds of years to return to

theclimax state.

Even the kind of stability defined assimple lack of change is not always

associated with maximum diversity. At leastin temperate zones,

maximum diversity is often found in mid-successionalstages, not in the

climax community. Once a redwood forest matures, forexample, the kinds

of species and the number of individuals growing on theforest floor are

reduced. In general, diversity, by itself, does not ensurestability.

Mathematical models of ecosystems likewise suggest that diversitydoes

not guarantee ecosystem stability—just the opposite, in fact. A

morecomplicated system is, in general, more likely than a simple system

to breakdown. A fifteen-speed racing bicycle is more likely to break down

than achild’s tricycle.

Ecologists are especially interested toknow what factors contribute to the

resilience of communities because climaxcommunities all over the world

are being severely damaged or destroyed by humanactivities. The

destruction caused by the volcanic explosion of Mount , in the

northwestern United States, for example, pales in comparison tothe

destruction caused by humans. We need to know what aspects of a

communityare most important to the community’s resistance to

destruction, as well as itsrecovery.

Many ecologists now think that the relativelong-term stability of climax

communities comes not from diversity but from the“patchiness” of the

environment, an environment that varies from place to placesupports

more kinds of organisms than an environment that is uniform. A

localpopulation that goes extinct is quickly replaced by immigrants from

an adjacentcommunity. Even if the new population is of a different

species, it canapproximately fill the niche vacated by the extinct

population and keep thefood web intact.

托福阅读试题

1. The word “particular” in the passage(paragraph 1) is closest in

meaning to

l

ic

x

2. According to paragraph 1, which of thefollowing is NOT true of climax

communities?

occur at the end of a succession.

last longer than any other type ofcommunity.

numbers of plants in them and the mixof species do not change.

remain stable for at least 500 yearsat a time.

3. According to paragraph 2, which of thefollowing principles of

ecosystems can be learned bystudying a pond?

tem properties change more slowlythan individuals in the

system.

stability of an ecosystem tends tochange as individuals are replaced.

dual organisms are stable from oneyear to the next.

D.A change in the members of an organismdoes not affect an

ecosystem’s properties.

4. According to paragraph 3, ecologistsonce believed that which of the

following illustratedthe most stableecosystems?

r communities

communities

-crop farmlands

sional plant communities

5. According to paragraph 4, why is thequestion of ecosystem stability

complicated?

reasons for ecosystem change are notalways clear.

ists often confuse the word“stability” with the word

“resilience.”

exact meaning of the word “stability”is debated by ecologists.

are many different answers toecological questions.

6. According to paragraph 4, which of thefollowing is true of climax

communities?

are more resilient than pioneercommunities.

can be considered both the most andthe least stable communities.

are stable because they recoverquickly after major disturbances.

are the most resilient communitiesbecause they change the least

over time.

7. Which of the following can be inferredfrom paragraph 5 about

redwood forests?

become less stable as they mature.

support many species when they reachclimax.

are found in temperate zones.

have reduced diversity duringmid-successional stages.

8. The word “guarantee” in the passage(paragraph 5) is closest in

meaning to

se

cate

9. In paragraph 5, why does the authorprovide the information that “A

fifteen-speed racing bicycle is more likely tobreak down than a child’s

tricycle”?

illustrate a general principle aboutthe stability of systems by using

an everyday example

demonstrate that an understanding ofstability in ecosystems can be

applied to help understand stability in othersituations

make a comparison that supports theclaim that, in general, stability

increases with diversity

provide an example that contradictsmathematical models of

ecosystems

10. The word “pales” in the passage(paragraph 6) is closest in meaning

to

ses proportionally

s

significance

common

11. Which of the sentences below bestexpresses the essential information

in the highlighted sentence in the passage(paragraph 7)? Incurred

choices change the meaning in important ways or leaveout essential

information.

ists now think that the stabilityof an environment is a result of

diversity rather than patchiness.

environments that vary from placeto place do not often have

high species diversity.

m environments cannot be climaxcommunities because they do

not support as many types of organisms as patchyenvironments.

D.A patchy environment is thought toincrease stability because it is able

to support a wide variety of organisms.

12. The word “adjacent” in the passage(paragraph 7) is closest in

meaning to

n

oring

13. Look at the four squares [█] thatindicate where the following sentence

could be added to the passage. In fact,damage to the environment by

humans is often much more severe than damage bynatural events and

processes.

█【A】Ecologists are especially interested to know what factors

contributeto the resilience of communities because climax communities

all over the worldare being severely damaged or destroyed by human

activities. █【B】The destructioncaused by the volcanic explosion of

Mount St. Helens, in the northwesternUnited States, for example, pales in

comparison to the destruction caused byhumans. █【C】We need toknow

what aspects of a community are most important to the community’sresistance to destruction, as well as its recovery. █【D】

Where would the sentence best fit? Click ona square to add the sentence

to the passage.

14. Directions: Anintroductory sentence for a brief summary of the

passage is provided te the summary by selecting the

THREE answer choices that express themost important ideas in the

passage. Some sentences do not belong in thesummary because they

express ideas that are not presented in the passage or areminor ideas in

the passage. This question is worth 2 points.

The process of succession and the stabilityof a climax community can

change over time.

changes that occur in an ecosystemfrom the pioneer to the climax

community can be seen in one human generation.

B.A high degree of species diversity doesnot always result in a stable

ecosystem.

level of resilience in a plantcommunity contributes to its long-term

stability.

ists agree that climax communitiesare the most stable types of

ecosystems.

eements over the meaning of theterm “stability” make it

difficult to identify the most stable ecosystems.

resilience of climax communitiesmakes them resistant to

destruction caused by humans.

托福阅读答案

1. particular特别的，特定的，答案specific。前文说assemblethem flexibly，多变的，就是每个落都不一样，强调特殊性。A自然B最终D复杂都与前文不搭，所以都不对

2.以climax communities做关键词定位至原文第三句和最后一句，第三句说明A对，不选；最后一句说明D对，不选；B没直说，说其他的communities 变化周期在1-500年，climax最少是500年，说明climax最长，B对，不选。而且最后一句也说了climax是变化的，C说反了，选

3.本段非常短，迅速看完之后发现最后一句是结论，说生态系统比组成生态系统的任意单一物种都稳定，A是答案

4.以ecologists做关键词定位至本段第一句，说生态学家认为生态系统中物种越多越稳定。接着在举例子的时候作者举到了climax communities，说明生态学家认为climax communities最稳定，答案B

5.以question ofecosystem stability为关键词定位至本段头两句，说生态学家对于什么是生态系统的稳定性依然存在争议，C是原文的忠实改写

6.关于climax communities原文有两个地方提到。因为生态学家对什么是稳定这个问题存在两个观点，以不变这种观点看，climax是最稳定的，以快速恢复这种观点看，climax是最不稳定的，所以climax既稳定也不稳定，B明确说到两个方面，其它选项都只说到一个方面

7.以redwood forest做关键词定位至原文第三句，事实上这个redwood是前句的一个具体例子，前面句说至少在温带，mid是最稳定的，不是climax，紧接着就举了一个redwood的例子，可以推断redwood是温带植物，C是答案。A/B/D都与原文意思相反，而且B和D基本上意思一样，都不对

8.本句中有个likewise，说明它与前面句子构成类比，前句说diversity does not

ensure stability, 后文的内容几乎和前句一模一样，除了动词被替换，因此guarantee的意思就是ensure

9.括号的作用是解释括号之前的文字，前文说系统越复杂越容易坏，后面举了十五速赛车和小孩子的三轮车的例子，三轮车明显比赛车简单，所以就是支持前文，A正确，C正好说反，其他都没说

苍白，使什么什么苍白之意。单词所在句之前说很多climax

communities都被人类破坏了，也就是强调人的破话很严重。后面举了个例子，说圣海伦斯火山爆发造船的破坏还没有人类活动的破坏严重，所以C选项lose

significance正确

11.原文的结构是生态系统的长期稳定性不是因为blablabla，而是因为blablabla，又对这个进行了解释，说物种多；A说反；B错，因为原文没有说patchiness和diversity是矛盾的；C错，因为原文比较的是patchiness和uniform，而C直接将patchiness和climax进行比较，偷换概念；D正确，注意原文貌似没有明显的因果关系，因此可能单看句子间关系的话会排除D，但原文后半句整个是对patchiness的一种解释，所以存在不明显的因果关系

nt是相邻之意，原文说本地的population灭绝的话会被哪里来的落补充，可能的只有foreign和neighboring，这两个选项代入原文都是可以的，除知道这个单词的意思之外，还可以认为相邻的落更有可能迅速补充，而外来的范围太大，不对

13.根据待插入句中的human判断，A/B/C是可能的，naturalevents and

processes自然的过程，与第二句中的圣海伦斯火山爆发是同义替换，所以B/C可能正确，但按照先理论后实例的原则，正确答案是B不是C

nges选项与原文首段的最后一句意思相反，不选

A high degree选项对应原文第三段和第五段的首句，第四段的最后一句，正确

The level选项对应原文第六段首句，第四段倒数第二第三句，正确

Ecologists选项与原文第三段第四段的首句意思相反，不选

Disagreements选项对应原文第四段第二句，正确

The resilience选项原文没说，原文第六段说不知道为什么生物落能抵抗破坏，不选