托福阅读TPO3(试题+答案+译文)第3篇:TheLong-TermStabilityofEcosystems
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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 St.Helens, 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
A.natural
B.final
C.specific
D.complex
2. According to paragraph 1, which of thefollowing is NOT true of climax communities?
A.They occur at the end of a succession.
B.They last longer than any other type ofcommunity.
C.The numbers of plants in them and the mixof species do not change.
D.They 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?
A.Ecosystem properties change more slowlythan individuals in the system.
B.The stability of an ecosystem tends tochange as individuals are replaced.
C.Individual 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?
A.Pioneer communities
B.Climax communities
C.Single-crop farmlands
D.Successional plant communities
5. According to paragraph 4, why is thequestion of ecosystem stability complicated?
A.The reasons for ecosystem change are notalways clear.
B.Ecologists often confuse the word“stability” with the word “resilience.”
C.The exact meaning of the word “stability”is debated by ecologists.
D.There are many different answers toecological questions.
6. According to paragraph 4, which of thefollowing is true of climax communities?
A.They are more resilient than pioneercommunities.
B.They can be considered both the most andthe least stable communities.
C.They are stable because they recoverquickly after major disturbances.
D.They are the most resilient communitiesbecause they change the least over time.
7. Which of the following can be inferredfrom paragraph 5 about redwood forests?
A.They become less stable as they mature.
B.They support many species when they reachclimax.
C.They are found in temperate zones.
D.They have reduced diversity duringmid-successional stages.
8. The word “guarantee” in the passage(paragraph 5) is closest in meaning to
A.increase
B.ensure
C.favor
D.complicate
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”?
A.To illustrate a general principle aboutthe stability of systems by using an everyday example
B.To demonstrate that an understanding ofstability in ecosystems can be applied to help understand stability in othersituations
C.To make a comparison that supports theclaim that, in general, stability increases with diversity
D.To provide an example that contradictsmathematical models of ecosystems
10. The word “pales” in the passage(paragraph 6) is closest in meaning to
A.increases proportionally
B.differs
C.loses significance
D.is 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.
A.Ecologists now think that the stabilityof an environment is a result of diversity rather than patchiness.
B.Patchy environments that vary from placeto place do not often have high species diversity.
C.Uniform 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
A.foreign
B.stable
C.fluid
D.neighboring
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 below.Complete 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.
A.The 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.
C.The level of resilience in a plantcommunity contributes to its long-term stability.
D.Ecologists agree that climax communitiesare the most stable types of ecosystems.
E.Disagreements over the meaning of theterm “stability” make it difficult to identify the most stable ecosystems.
F.The 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，就是每个群落都不一样，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
10.pale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clima_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
12.adjacent是相邻之意，原文说本地的population灭绝的话会被哪里来的群落补充，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，还可以认为相邻的群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
14.Thechanges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群落能抵抗破坏，不选
托福阅读译文
植物群体可以自由地聚集，它们特殊的结构取决于聚集区域的具体历史。生态学家使用“演替”来诠释植物群落和生态系统随着时间推移所发生的变化。演替中的第一个群落被称作先锋群落，而处于演替最后那个长期生存的群落被称为顶极群落。先锋群落和紧接着的植物群落的变化周期是从1到500年不等，植物数量和混合种类数量的变化是慢慢积累的。顶极群落本身也改变，但其变化周期超过500 年。
现代一个研究池塘的生态学会发现池塘在一年当中相对而言是不变的。个别鱼类可能被替换，但年复一年鱼的总数都趋于一致。也就是说，一个生态系统自身的属性要比由单一生物体组成的生态系统更稳定。
生态学家们一度认为物种的多样性使生态系统稳定，生态系统物种越多样则生态系统越稳定。通过观察得出的结论支持了这个观点，长期持久的顶极群落通常要比先锋群落具备更为复杂的食物网和更多的物种。生态学家家们得出的结论是：顶点生态系统的稳定性明显取决于他们的复杂化程度。举个极端的例子，在单一作物的农田中，一年的恶劣天气或单一害虫的入侵就可以摧毁所有作物。与此相反，在一个复杂的顶极群落里，如温带森林，他们便可以抵御来自气候和害虫的干扰和入侵。
不管怎样，生态系统稳定性的问题非常复杂。首先，不是所有的生态学家都赞同“稳定”的含义。稳定性可以简单地定义为缺乏变化。如果是这样的话，顶极群落将被视为最稳定的，因为根据定义，他们随着时间推移而变化得最少。另外，稳定性也可以界定为生态系统在经历了严重破坏之后回复原貌的速度，比如火灾。这种稳定性也被称作弹性。在这种情况下，顶极群落将是最脆弱和最不稳定的，因为他们可能需要数百年时间才能恢复到顶点状态。
即使是这种被定义为简单地缺乏变化的稳定性并非总是与最多样的物种联系起来。至少在温带地区，会经常在演替过程中发现最多物种，而不是在顶极群落中。例如，红杉树林一旦成熟，其中的物种数量以及单个物种的数量都会减少。一般来说，多样性本身并不能保证稳定性(事实上正相反)，生态系统的数学模型也可以得出同样的结论。一个更复杂的系统可能比一个简单的系统更容易被破坏(一个十五速的赛车比一个孩子的三轮车更容易损坏)。
生态学家们更想弄清楚到底哪些因素有助于促成群落的恢复，因为世界各地的顶极群落都因为人类活动而遭受到严重的损坏或毁坏。就像美国西北部圣海伦火山的猛烈喷发所造成的破坏，在人类活动对环境造成的破坏面前也相形见绌。我们必须了解对群落抵抗、破坏和恢复来说哪些是最重要的。
现在的很多生态学家们认为，顶极群落相对长期的稳定性并非来自于多样性，而是来自环境的“补缀”，随处变化的环境比始终如一的环境更有利于多种有机体的生存。当地物种灭亡后，马上就会被相邻群落的移民取代。即便是另一种不同的物种，他们也可以填补那些已灭绝生物的空缺，并保持食物网的完整。
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