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TPO 32—1 Plant Colonization
原文：
【1】Colonization is one way in which plants can change the ecology of a site. Colonization is a process with two components: invasion and survival. The rate at which a site is colonized by plants depends on both the rate at which individual organisms (eds, spores, immature or mature 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 for colonization—a safe site where disturbance by fire or by cutting down of trees has either removed competing species or reduced levels of competition and other negative interactions to 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, infertile site becau of poor survival on the latter. A fertile, plowed field is rapidly invaded by a large variety of weeds, whereas a neighboring construction site from which the soil has beencompacted or removed to expo a coar, infertile parent material may remain virtually free of vegetation for many months or even years despite receiving the same input of eds as the plowed field. 【2】Both the rate of invasion and the rate of extinction vary greatly among different plant species. Pioneer species—tho that occur only in the earliest stages of colonization—tend to have high rates of invasion becau they produce very large numbers of reproductive propagules (eds, spores, and so on) and becau they have an efficient means of dispersal (normally, wind).小鸡卡通
【3】If colonizers produce short-lived reproductive propagules, then they must produce very large numbers unless they have an efficient means of dispersal to suitable new habitats. Many plants dep
end on wind for dispersal and produce abundant quantities of small, relatively short-lived eds to compensate for the fact that wind is not always a reliable means of reaching the appropriate type of habitat. Alternative strategies have evolved in some plants, such as tho that produce fewer but larger eds that are disperd to suitable sites by birds or small mammals or tho that produce long-lived eds. Many forest plants em to exhibit the latter adaptation, and viable eds of pioneer species can be found in large numbers on some forest floors. For example, as many as 1,125 viable eds per square meter were found in a 100-year-old Douglas fir/western hemlock forest in coastal British Columbia. Nearly all the eds that had germinated from this ed bank were from pioneer species. The rapid colonization ofsuch sites after disturbance is undoubtedly in part a reflection of the large ed bank on the forest floor.
【4】An adaptation that is well developed in colonizing species is a high degree of variation in germination (the beginning of a ed's growth). Seeds of a given species exhibit a wide range of germination dates, increasing the probability that at least some of the eds will germinate during a period of favorable environmental conditions. This is particularly important for species that colonize an environment where there is no existing vegetation to ameliorate climatic extremes and in which there may be great climatic diversity.
【5】Species succession in plant communities, i.e., the temporal quence of
appearance and disappearance of species is dependent on events occurring at different stages in the life history of a species. Variation in rates of invasion and growth plays an important role in determining patterns of succession, especially condary succession. The species that are first to colonize a site are tho that produce abundant ed that is distributed successfully to new sites. Such species generally grow rapidly and quickly dominate new sites, excluding other species with lower invasion and growth rates. The first community that occupies a disturbed area therefore may be compod of species with the highest rate of invasion, whereas the community of the subquent stage may consist of plants with similar survival rates but lower invasion rates.
题目：白板课件
1.According to paragraph 1, how does disturbance of a site influence its colonization by a plant species?
A.Disturbance reduces or eliminates competition by other species.
B.Disturbance increas negative interactions with other organisms on the site.
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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 clost in meaning to
金毛多少钱一只A.almost totally.
B.unusually.
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D.unnaturally.
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3.Why does the author mention a plowed field and a construction site in the passage?
A.T o 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.T o explain that exposing or compacting the soil results in successful colonization.
4.The word "despite"(paragraph 1) in the passage is clost in meaning to
A.without.
B.almost never.
C.even though.风景画图片
D.perhaps.
5.Which of the ntences below best express the esntial information in the highlighted ntence in the passage (paragraph 2)? Incorrect choices change the meaning in important ways or leave out esntial information.
A.The eds of pioneer species are usually carried by the wind to fertile sites, where they reproduce very efficiently.
B.Pioneer species are successful invaders becau they produce lots of eds that are disperd effectively.
C.Pioneer species produce their largest numbers of propagules during the earliest stages of their colonization.
