托福閱讀TPO3(試題+答案+譯文)第3篇:TheLong-TermStabilityofEcosystems
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托福閱讀原文
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.
托福閱讀試題
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.
托福閱讀答案
1. particular特別的，特定的，答案specific。前文說assemblethem flexibly，多變的，就是每個群落都不一樣，強調特殊性。A自然B最終D復雜都與前文不搭，所以都不對
2.以climax communities做關鍵詞定位至原文第三句和最后一句，第三句說明A對，不選;最后一句說明D對，不選;B沒直說，說其他的communities 變化周期在1-500年，climax最少是500年，說明climax最長，B對，不選。而且最后一句也說了climax是變化的，C說反了，選
3.本段非常短，迅速看完之后發(fā)現(xiàn)最后一句是結論，說生態(tài)系統(tǒng)比組成生態(tài)系統(tǒng)的任意單一物種都穩(wěn)定，A是答案
4.以ecologists做關鍵詞定位至本段第一句，說生態(tài)學家認為生態(tài)系統(tǒng)中物種越多越穩(wěn)定。接著在舉例子的時候作者舉到了climax communities，說明生態(tài)學家認為climax communities最穩(wěn)定，答案B
5.以question ofecosystem stability為關鍵詞定位至本段頭兩句，說生態(tài)學家對于什么是生態(tài)系統(tǒng)的穩(wěn)定性依然存在爭議，C是原文的忠實改寫
6.關于climax communities原文有兩個地方提到。因為生態(tài)學家對什么是穩(wěn)定這個問題存在兩個觀點，以不變這種觀點看，climax是最穩(wěn)定的，以快速恢復這種觀點看，climax是最不穩(wěn)定的，所以climax既穩(wěn)定也不穩(wěn)定，B明確說到兩個方面，其它選項都只說到一個方面
7.以redwood forest做關鍵詞定位至原文第三句，事實上這個redwood是前句的一個具體例子，前面句說至少在溫帶，mid是最穩(wěn)定的，不是climax，緊接著就舉了一個redwood的例子，可以推斷redwood是溫帶植物，C是答案。A/B/D都與原文意思相反，而且B和D基本上意思一樣，都不對
8.本句中有個likewise，說明它與前面句子構成類比，前句說diversity does not ensure stability, 后文的內容幾乎和前句一模一樣，除了動詞被替換，因此guarantee的意思就是ensure
9.括號的作用是解釋括號之前的文字，前文說系統(tǒng)越復雜越容易壞，后面舉了十五速賽車和小孩子的三輪車的例子，三輪車明顯比賽車簡單，所以就是支持前文，A正確，C正好說反，其他都沒說
10.pale蒼白，使什么什么蒼白之意。單詞所在句之前說很多climax communities都被人類破壞了，也就是強調人的破話很嚴重。后面舉了個例子，說圣海倫斯火山爆發(fā)造船的破壞還沒有人類活動的破壞嚴重，所以C選項lose significance正確
11.原文的結構是生態(tài)系統(tǒng)的長期穩(wěn)定性不是因為blablabla，而是因為blablabla，又對這個進行了解釋，說物種多;A說反;B錯，因為原文沒有說patchiness和diversity是矛盾的;C錯，因為原文比較的是patchiness和uniform，而C直接將patchiness和clima_行比較，偷換概念;D正確，注意原文貌似沒有明顯的因果關系，因此可能單看句子間關系的話會排除D，但原文后半句整個是對patchiness的一種解釋，所以存在不明顯的因果關系
12.adjacent是相鄰之意，原文說本地的population滅絕的話會被哪里來的群落補充，可能的只有foreign和neighboring，這兩個選項代入原文都是可以的，除知道這個單詞的意思之外，還可以認為相鄰的群落更有可能迅速補充，而外來的范圍太大，不對
13.根據待插入句中的human判斷，A/B/C是可能的，naturalevents and processes自然的過程，與第二句中的圣海倫斯火山爆發(fā)是同義替換，所以B/C可能正確，但按照先理論后實例的原則，正確答案是B不是C
14.Thechanges選項與原文首段的最后一句意思相反，不選
A high degree選項對應原文第三段和第五段的首句，第四段的最后一句，正確
The level選項對應原文第六段首句，第四段倒數(shù)第二第三句，正確
Ecologists選項與原文第三段第四段的首句意思相反，不選
Disagreements選項對應原文第四段第二句，正確
The resilience選項原文沒說，原文第六段說不知道為什么生物群落能抵抗破壞，不選
托福閱讀譯文
植物群體可以自由地聚集，它們特殊的結構取決于聚集區(qū)域的具體歷史。生態(tài)學家使用“演替”來詮釋植物群落和生態(tài)系統(tǒng)隨著時間推移所發(fā)生的變化。演替中的第一個群落被稱作先鋒群落，而處于演替最后那個長期生存的群落被稱為頂極群落。先鋒群落和緊接著的植物群落的變化周期是從1到500年不等，植物數(shù)量和混合種類數(shù)量的變化是慢慢積累的。頂極群落本身也改變，但其變化周期超過500 年。
現(xiàn)代一個研究池塘的生態(tài)學會發(fā)現(xiàn)池塘在一年當中相對而言是不變的。個別魚類可能被替換，但年復一年魚的總數(shù)都趨于一致。也就是說，一個生態(tài)系統(tǒng)自身的屬性要比由單一生物體組成的生態(tài)系統(tǒng)更穩(wěn)定。
生態(tài)學家們一度認為物種的多樣性使生態(tài)系統(tǒng)穩(wěn)定，生態(tài)系統(tǒng)物種越多樣則生態(tài)系統(tǒng)越穩(wěn)定。通過觀察得出的結論支持了這個觀點，長期持久的頂極群落通常要比先鋒群落具備更為復雜的食物網和更多的物種。生態(tài)學家家們得出的結論是：頂點生態(tài)系統(tǒng)的穩(wěn)定性明顯取決于他們的復雜化程度。舉個極端的例子，在單一作物的農田中，一年的惡劣天氣或單一害蟲的入侵就可以摧毀所有作物。與此相反，在一個復雜的頂極群落里，如溫帶森林，他們便可以抵御來自氣候和害蟲的干擾和入侵。
不管怎樣，生態(tài)系統(tǒng)穩(wěn)定性的問題非常復雜。首先，不是所有的生態(tài)學家都贊同“穩(wěn)定”的含義。穩(wěn)定性可以簡單地定義為缺乏變化。如果是這樣的話，頂極群落將被視為最穩(wěn)定的，因為根據定義，他們隨著時間推移而變化得最少。另外，穩(wěn)定性也可以界定為生態(tài)系統(tǒng)在經歷了嚴重破壞之后回復原貌的速度，比如火災。這種穩(wěn)定性也被稱作彈性。在這種情況下，頂極群落將是最脆弱和最不穩(wěn)定的，因為他們可能需要數(shù)百年時間才能恢復到頂點狀態(tài)。
即使是這種被定義為簡單地缺乏變化的穩(wěn)定性并非總是與最多樣的物種聯(lián)系起來。至少在溫帶地區(qū)，會經常在演替過程中發(fā)現(xiàn)最多物種，而不是在頂極群落中。例如，紅杉樹林一旦成熟，其中的物種數(shù)量以及單個物種的數(shù)量都會減少。一般來說，多樣性本身并不能保證穩(wěn)定性(事實上正相反)，生態(tài)系統(tǒng)的數(shù)學模型也可以得出同樣的結論。一個更復雜的系統(tǒng)可能比一個簡單的系統(tǒng)更容易被破壞(一個十五速的賽車比一個孩子的三輪車更容易損壞)。
生態(tài)學家們更想弄清楚到底哪些因素有助于促成群落的恢復，因為世界各地的頂極群落都因為人類活動而遭受到嚴重的損壞或毀壞。就像美國西北部圣海倫火山的猛烈噴發(fā)所造成的破壞，在人類活動對環(huán)境造成的破壞面前也相形見絀。我們必須了解對群落抵抗、破壞和恢復來說哪些是最重要的。
現(xiàn)在的很多生態(tài)學家們認為，頂極群落相對長期的穩(wěn)定性并非來自于多樣性，而是來自環(huán)境的“補綴”，隨處變化的環(huán)境比始終如一的環(huán)境更有利于多種有機體的生存。當?shù)匚锓N滅亡后，馬上就會被相鄰群落的移民取代。即便是另一種不同的物種，他們也可以填補那些已滅絕生物的空缺，并保持食物網的完整。
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