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【1】Colonization is one way in which plants can change the ecology of a site. Colonization is aprocess with two components: invasion and survival. The rate at which a site is colonized byplants depends on both the rate at which individual organisms (seeds, spores, immature ormature individuals) arrive at the site and their success at becoming established and surviving.Success in colonization depends to a great extent on there being a site available forcolonization—a safe site where disturbance by fire or by cutting down of trees has eitherremoved competing species or reduced levels of competition and other negative interactionsto a level at which the invading species can become established. For a given rate of invasion,colonization of a moist, fertile site is likely to be much more rapid than that of a dry, infertilesite because of poor survival on the latter. A fertile, plowed field is rapidly invaded by a largevariety of weeds, whereas a neighboring construction site from which the soil hasbeencompacted or removed to expose a coarse, infertile parent material may remain virtuallyfree of vegetation for many months or even years despite receiving the same input of seeds asthe plowed field.
【2】Both the rate of invasion and the rate of extinction vary greatly among different plantspecies. Pioneer species—those that occur only in the earliest stages of colonization—tend tohave high rates of invasion because they produce very large numbers of reproductivepropagules (seeds, spores, and so on) and because they have an efficient means of dispersal(normally, wind).
【3】If colonizers produce short-lived reproductive propagules, then they must produce verylarge numbers unless they have an efficient means of dispersal to suitable new habitats. Manyplants depend on wind for dispersal and produce abundant quantities of small, relativelyshort-lived seeds to compensate for the fact that wind is not always a reliable means ofreaching the appropriate type of habitat. Alternative strategies have evolved in some plants,such as those that produce fewer but larger seeds that are dispersed to suitable sites bybirds or small mammals or those that produce long-lived seeds. Many forest plants seem toexhibit the latter adaptation, and viable seeds of pioneer species can be found in largenumbers on some forest floors. For example, as many as 1,125 viable seeds per square meterwere found in a 100-year-old Douglas fir/western hemlock forest in coastal British Columbia.Nearly all the seeds that had germinated from this seed bank were from pioneer species. Therapid colonization ofsuch sites after disturbance is undoubtedly in part a reflection of thelarge seed bank on the forest floor.
【4】An adaptation that is well developed in colonizing species is a high degree of variation ingermination (the beginning of a seed's growth). Seeds of a given species exhibit a widerange of germination dates, increasing the probability that at least some of the seeds willgerminate during a period of favorable environmental conditions. This is particularly importantfor species that colonize an environment where there is no existing vegetation to ameliorateclimatic extremes and in which there may be great climatic diversity.
【5】Species succession in plant communities, i.e., the temporal sequence of appearanceand disappearance of species is dependent on events occurring at different stages in the lifehistory of a species. Variation in rates of invasion and growth plays an important role indetermining patterns of succession, especially secondary succession. The species that are firstto colonize a site are those that produce abundant seed that is distributed successfully tonew sites. Such species generally grow rapidly and quickly dominate new sites, excluding otherspecies with lower invasion and growth rates. The first community that occupies a disturbedarea therefore may be composed of species with the highest rate of invasion, whereas thecommunity of the subsequent stage may consist of plants with similar survival rates but lowerinvasion rates.
托福阅读试题
1.According to paragraph 1, how does disturbance of a site influence its colonizationby a plant species?
A.Disturbance reduces or eliminates competition by other species.
B.Disturbance increases negative interactions with other organisms on the site.
C.Disturbance prevents a plant species from colonizing a new site.
D.Disturbance reduces the fertility of a site.
2.The word "virtually" in the passage (paragraph 1) is closest in meaning to
A.almost totally.
B.unusually.
C.consistently.
D.unnaturally.
3.Why does the author mention a plowed field and a construction site in the passage?
A.To argue that sites that have been affected by human activity tend to be colonized slowly.
B.To illustrate the kind of sites that may be invaded by weeds.
C.To contrast sites in terms of their suitability for colonization.
D.To explain that exposing or compacting the soil results in successful colonization.
4.The word "despite"(paragraph 1) in the passage is closest in meaning to
A.without.
B.almost never.
C.even though.
D.perhaps.
5.Which of the sentences below best expresses the essential information in thehighlighted sentence in the passage (paragraph 2)? Incorrect choices change themeaning in important ways or leave out essential information.
A.The seeds of pioneer species are usually carried by the wind to fertile sites, where theyreproduce very efficiently.
B.Pioneer species are successful invaders because they produce lots of seeds that aredispersed effectively.
C.Pioneer species produce their largest numbers of propagules during the earliest stages oftheir colonization.
D.Pioneer species reproduce very quickly and efficiently because they produce very largenumber of seeds.
6.What can be inferred from paragraph 3 about the reason that large seeds aredispersed by birds or small animals rather than by wind?
A.Large seeds are easier for birds and animals to see than are the small seeds dispersed bythe wind.
B.Large seeds are too heavy for the wind to disperse.
C.Large seeds cannot be eaten by birds and animals.
D.Large seeds are short-lived and thus require a more efficient means of dispersal than smallseeds do.
7.The phrase "the latter adaptation" in the passage (paragraph 3) refers to
A.producing fewer seeds.
B.producing larger seeds.
C.dispersal by birds and small mammals.
D.producing long-lived seeds.
8.The word "viable" in the passage (paragraph 3) is closest in meaning to
A.able to survive.
B.individual.
C.large.
D.remaining.
9.The example of the 100-year-old Douglas fir/western hemlock forest in paragraph toillustrates which of the following ideas?
A.It is uncommon for older seed to germinate.
B.Pioneer species tend to prefer forest floors for colonization purposes.
C.Long-lived seeds of pioneer species can successfully germinate over long periods of time.
D.Coastal British Columbia is particularly suited for pioneer species to develop.
10.According to paragraph 4, how do plants manage to germinate in areas with greatclimatic diversity and climatic extremes?
A.By producing seeds only during favorable climatic conditions.
B.By generating large numbers of seeds.
C.By colonizing only those areas where other plants have survived.
D.By producing seeds that have a wide range of germination dates.
11.The word "abundant〃 in the passage (paragraph 5) is closest in meaning to
A.new.
B.improved.
C.suitable.
D.plentiful.
12.According to paragraph 5, which of the following determines the sequence in whichplant species will colonize a site?
A.The extent of growth of a species on a prior site before it begins to colonize a secondarysite.
B.The differences in invasion and growth rates across species.
C.The degree of fertility of a site.
D.The kind of disturbance that the site has undergone.
13. Look at the four squares [■] that indicate where the following sentence could beadded to the passage. Where does the sentence best fit? They require relatively littleprotection or nutrients.
Species succession in plant communities, i.e., the temporal sequence of appearance anddisappearance of species is dependent on events occurring at different stages in the lifehistory of a species.■【A】Variation in rates of invasion and growth plays an important role indetermining patterns of succession, especially secondary succession.■【B】The species thatare first to colonize a site are those that produce abundant seed that is distributedsuccessfully to new sites.■【C】Such species generally grow rapidly and quickly dominate newsites, excluding other species with lower invasion and growth rates. The first community thatoccupies a disturbed area therefore may be composed of species with the highest rate ofinvasion, whereas the community of the subsequent stage may consist of plants with similarsurvival rates but lower invasion rates.■【D】
14. Prose Summary
The ecology of a site is changed through its colonization by new plants that arrive andgrow there.
A.The species that first colonize a disturbed site are typically ones that produce a largenumber of efficiently dispersed seeds.
B.Plants that cannot successfully compete with other species can invade and colonize a siteonly if it is fertile and moist, such as a plowed field.
C.Pioneer species arrive at a site first but have lower survival rates than do species that arrivelater.
D.Producing seeds that germinate at various times over long periods allows some plants tocolonize sites that only occasionally present the right conditions for growth.
E.Large, long-lived seeds tend to result in large seed banks with short germination periodsrequiring favorable environmental conditions for development.
F.The successive appearance and disappearance of species on a site is a result of variationin species' rates of invasion, growth, and survival.
托福阅读答案
1.第1段第4句话，通过火灾和砍伐的干涉要么消除竞争对手要么降低竞争的强度。
2.virtually表示"实际上，几乎", 程度上对应almost totally。
3.第一段第5、6句话，肥沃的土地植物入侵的速度快，反之亦然。
4.despite 尽管，对应even though 尽管/即使。
5.原句强调了先锋物种入侵速度快的两个原因，一是能够产生大量可繁殖的种子，二是拥有有效的传播途径。原句和fertile sites没有关系，A错;C没有提到种子的繁殖力; D没有提到传播途径，只有B满足原句的条件。
6.第3段第2，3句：小种子通常靠风传播，大种子由鸟和动物实现传播。
7.the latter adaptation，后一种适应性，段落开头讲的是短命种子，所以后一种适应性是指长命种子。
8.viable，有生命力的，对应A。
9.该例子的前一句话为观点句, 例子是为了说明观点，即长命种子在森林地面上很繁荣。
10.该段的第1句话，发芽时间的变化。
11.abundant，表示"丰富的"，对应D。
12.该段第二句话，succession 对应colonize a site。
13.they指代species. 原句说该物种的生存要求很低，就意味着他们更能存活，原句接下去可能阐述该物种如何靠着该优势来侵占土地繁殖。
14.A选项: 对应第2段的核心意思，第2句话;
B选项: 原文中没有明确说明的信息;
C选项: 违背原文意思，第三段最后一句;
D选项: 对应第4段的核心意思;
E选项: requiring favorable environmental conditions for development是原文中没有明确说明的信息;
F选项: 对应第5段的核心意思。
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