Official 32 Passage 3

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Plant Colonization

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According to paragraph 1, how does disturbance of a site influence its colonization by a plant species?

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  • 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.
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正确答案: A

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  • 译文
  • 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 (seeds, 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 because 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 been compacted or removed to expose a coarse, infertile parent material may remain virtually free of vegetation for many months or even years despite receiving the same input of seeds as the plowed field.



    Both the rate of invasion and the rate of extinction vary greatly among different plant species. Pioneer species-those that occur only in the earliest stages of colonization-tend to have high rates of invasion because they produce very large numbers of reproductive propagules (seeds, spores, and so on) and because they have an efficient means of dispersal (normally, wind).



    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 depend on wind for dispersal and produce abundant quantities of small, relatively short-lived seeds 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 those that produce fewer but larger seeds that are dispersed to suitable sites by birds or small mammals or those that produce long-lived seeds. Many forest plants seem to exhibit the latter adaptation, and viable seeds of pioneer species can be found in large numbers on some forest floors. For example, as many as 1,125 viable seeds per square meter were 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. The rapid colonization of such sites after disturbance is undoubtedly in part a reflection of the large seed bank on the forest floor.



    An adaptation that is well developed in colonizing species is a high degree of variation in germination (the beginning of a seed`s growth). Seeds of a given species exhibit a wide range of germination dates, increasing the probability that at least some of the seeds 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.



    Species succession in plant communities, i.e., the temporal sequence 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 secondary succession. The species that are first to colonize a site are those that produce abundant seed 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 composed of species with the highest rate of invasion, whereas the community of the subsequent stage may consist of plants with similar survival rates but lower invasion rates.


  • 移居是植物改变某个地点生态环境的方式之一。 移居过程包括两个阶段:入侵和存活。 一个地点被植物移居的速度取决于个体生物(种子、孢子、不成熟或成熟的个体)到达该地点并成功存活下来的速度。 移居的成功很大程度上取决于有一个合适的移居地点——一个安全的地点,因为火或伐树造成的干扰移除了竞争物种,或者将竞争和其他消极作用降低到了入侵物种能够移居的水平。入侵的速度既定,移居潮湿的、富饶的地点比移居干燥的、贫瘠的地点要快得多,因为在后者上存活率很低。 一块富饶的、耕耘过的田地会很快地被一大批种子入侵,然而临近一个土壤被压实了或暴露在粗糙贫瘠的基质上的建筑工地,可能几个月甚至几年都寸草不生,尽管得到了和耕作田地一样的种子。

    不同植物种类的入侵速度和灭绝速度都有很大不同。 先锋物种——那些只出现在移居最早期阶段的物种——倾向于拥有高的入侵速度,因为它们能够产生大量的繁殖体(种子、孢子等),而且有高效的传播方式(通常是风)。

    如果移居植物产生的是寿命短的繁殖体,它们必须大量生产,除非它们有一个有效的传播方式到达新的适宜的栖息地。 许多植物依靠风来传播种子;它们产生大量小的、相对短命的种子,以弥补一个事实:风不总是可靠的到达适当栖息地的方式。 有些植物则进化出了另外的策略,例如有些植物产生数量较少却较大的种子,这些种子依靠鸟类或小型哺乳动物来被传播合适的地点,又如有些植物产生寿命长的种子。 许多森林植物似乎都展示了后一种适应性,在森林的地面上能发现大量先锋物种有繁殖力的种子。 例如,在英国哥伦比亚海岸有100年历史的道格拉斯冷杉/西部铁杉森林里,每平方米能找到1125粒有繁殖力的种子。 这个种子库里的几乎所有发芽的种子都是先锋物种留下的。 这些地点在扰乱后被快速移居,毫无疑问在一定程度上反映了林地里大量种子库的存在。

    在定居物种中得到很好发展的一种适应机制是萌芽期(即种子生长的开始)的很大差别。 某个物种的种子在萌芽时间上会表现出较大的范围,以此来增加至少有一些种子可以在最适宜的条件下萌发的可能性。 这一点对于在没有现存的植被改善极端气候以及气候非常多变的环境中定居的物种尤其重要。

    植物群落中的物种演替,即物种出现和消失的时间顺序,取决于在某一物种生活史不同阶段所发生的事件。 入侵和生长速度的不同在决定演替模式中发挥了重要作用,特别是在次生演替中。 在一个地点初次移居的物种是那些产生大量种子并成功传播的物种。 这些物种一般长得快,并很快控制新的领地,阻止其他入侵和生长速度低的物种的进入。 因此,第一个占领受干扰地区的群落可能包含入侵速度最快的物种,然而下一个阶段的群落可能包含具有相似存活率但较低入侵速度的物种。
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    解析

    【解析】

    题型分类:事实信息题

    题干分析:用题干关键词"disturbance"定位到第1段第4句话

    原文定位: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. 这里说了,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。这和A选项中的eliminates competition呼应。

    选项分析:

    B选项的increase negative interations和原文reduced other negative interations相反,所以错;C说反;

    D在原文无提及。

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