托福阅读原文TPO31-33

托福阅读TPO31第1篇
Speciation in Geographically Isolated Populations
Evolutionary biologists believe that speciation, the formation of a new species, often begins when some kind of physical barrier arises and divides a population of a single species into separate subpopulations. Physical separation between subpopulations promotes the formation of new species because once the members of one subpopulation can no longer mate with members of another subpopulation, they cannot exchange variant genes that arise in one of the subpopulations. In the absences of gene flow between the subpopulations, genetic differences between the groups begin to accumulate. Eventually the subpopulations become so genetically distinct that they cannot interbreed even if the physical barriers between them were removed. At this point the subpopulations have evolved into distinct species. This route to speciation is known as allopatry (“alio-” means “different”，and “patria” means “homeland”).
进化⽣生物学家认为物种形成(也就是新物种的产⽣生)经常是某种物理理障碍(地理理隔离)的出现把⼀一个单⼀一物种群分为隔离的亚种群。

亚种群的身体隔离促进了了新物种的产⽣生，因为⼀一旦亚种群中的成员⽆无法与其他亚种群中的成员交配，那么亚种群之间就没有变种基因的交换。

缺乏了了基因交流，亚种群之间的遗传差异就开始变⼤大。

最终这些亚种群的基因差异变得⼗十分明显，以⾄至于它们⽆无法进⾏行行种族内的交配，即使它们之间的物理理障碍已经消除。

这时，这些亚种族就演化成了了独⽴立的物种。

这样的物种形成的⽅方式被称作异域性(“alio-”意思是“不不同的”,“patria”意为“故乡”)。

Allopatric speciation may be the main speciation route. This should not be surprising, since allopatry is pretty common. In general, the subpopulations of most species are separated from each other by some measurable distance. So even under normal situations the gene flow among the subpopulations is more of an intermittent trickle than a steady stream. In addition, barriers can rapidly arise and shut offthe trickle. For example, in the1800s a monstrous earthquake changed the course of the Mississippi River, a large river flowing in the central part of the United States of America. The change separated populations of insects now living along opposite shore, completely cutting offgene flow between them.
异域性物种形成可能是最主要的物种形成⽅方式。

这没什什么惊讶的，因为异域现象太常⻅见。

⼀一般⽽而⾔言，⼤大多数的物种的亚种族都是被遥远距离所隔开，所以即使在正常条件下，这些亚物种间的基因流动倒更更像是⼀一条断断续续的细流，⽽而不不是⼀一条不不停流淌的⼩小溪。

并且，障碍也会迅速出现来截断这条细流。

例例如，19世纪的⼀一次⼤大地震改变了了密⻄西⻄西⽐比河(美国中部的⼀一条⼤大河)的流向，这个变化使得当地的昆⾍虫分离开来，它们现在居住于河的两岸，彼此的基因流动已被完全截断。

Geographic isolation also can proceed slowly, over great spans of time. We find evidence of such extended events in the fossil record, which affords glimpses into the breakup of formerly continuous environments. For example, during past ice ages, glaciers advanced down through North America and Europe and gradually cut off parts of populations from one another. When the glacier retreated, the separated populations of plants and animals
came into contact again. Some groups that had descended from the same parent population were no longer reproductively compatible—they had evolved into separate species. In other groups, however, genetic divergences had not proceeded so far, and the descendants could still interbreed—for them, reproductive isolation was not completed, and so speciation had not occurred.
地理理隔离也能缓慢地进⾏行行，会跨越很⻓长的时间段。

我们在化⽯石记录中找到了了这种⻓长期证据，从中我们可以瞥⻅见先前延续环境的破碎。

⽐比如说，在过去的冰河世纪，经过北北美和欧洲的冰川最终把种群的部分彼此切断，当冰川消退后，这些分离的动植物种群⼜又会连到⼀一起。

⼀一些起源于同⼀一⺟母群的群体变得不不再那么容易易兼容——它们演化成了了分开的物种。

然⽽而，在另⼀一些群体⾥里里，遗传差异并没有那么明显，后代们还是可以种族内互相交配的繁殖，隔离并没有彻底，所以物种形成就没有发⽣生。

Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth’s surface. About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the AtlanticOcean from the Pacific Ocean. This division set the stage for allopatric speciation among populations of fishes and other marine species.
异域性物种的形成也可能是由构成地球表⾯面的地壳构造板块运动所产⽣生的，这个运动虽略略微缓慢但却异常剧烈烈。

⼤大约五百万年年前这种地质运动形成了了连接北北美和南美的⼤大陆桥，也就是我们今天所说的巴拿⻢马地峡。

巴拿⻢马地峡的形成对全球洋流的模式产⽣生了了重⼤大的影响。

之前，⼤大陆间的这个缺⼝口可以让⽔水⾃自由流动，⽽而现在巴拿⻢马地峡在⼤大⻄西洋和太平洋之间形成了了⼀一道屏障。

这个地域分割为⻥鱼和其他海海洋物种的异域性物种形成创造了了条件。

In the 1980s, John Graves studied two populations of closely related fishes, one population from the Atlantic side of isthmus, the other from the Pacific side. He compared four enzymes found in the muscles of each population. Graves found that all four Pacific enzymes function better at lower temperatures than the four Atlantic versions of the same enzymes. This is significant because Pacific seawater is typically 2 to 3 degrees cooler than seawater on the Atlantic side of isthmus. Analysis by gel electrophoresis revealed slight differences in amino acid sequence of the enzymes of two of the four pairs. This is significant because the amino acid sequence of an enzyme is determined by genes.
20世纪80年年代，约翰??格雷雷夫斯研究了了两个紧密相关的⻥鱼种，⼀一种来⾃自地峡的⼤大⻄西洋⼀一侧，另⼀一种来⾃自太平洋那⼀一侧。

他⽐比较了了每个⻥鱼种肌⾁肉⾥里里的四种酶。

格雷雷夫斯发现在低温条件下，位于太平洋⼀一侧的⻥鱼种⾥里里的全部四类酶⽐比⼤大⻄西洋⼀一侧的四种酶功能更更好。

这个发现很重要，因为太平洋的海海⽔水的⽔水温通常要⽐比地峡另⼀一侧⼤大⻄西洋的海海⽔水低2到3度。

凝胶电泳的分析显示，四对中的两对酶的氨基酸序列列略略有不不同。

这也很重要，因为酶的氨基酸序列列是由基因决定的。

Graves drew two conclusions from these observations. First, at least some of the observed differences between the enzymes of the Atlantic and Pacific fish populations were not random but were the result of evolutionary adaption. Second, it appears that closely related populations of fishes on both sides of the isthmus are starting to genetically diverge from each other. Because Graves’s study of geographically isolated populations of isthmus fishes offers a glimpse of the beginning of a process of gradual accumulation of mutations that are neutral or adaptive, divergences here might be evidence of allopatric speciation in process.
根据这些观测，格雷雷夫斯得出了了两个结论。

第⼀一，在这些观测到的⼤大⻄西洋和太平洋⻥鱼种体内酶的差异中，⾄至少有⼀一些不不是偶然的，它们是适应进化的结果。

第⼆二，似乎地峡两侧原本密切相关的⻥鱼种开始有了了基因分化。

因为格雷雷夫斯关于地峡⻥鱼类地域隔离的种群研究为中性或适应性突变的逐渐累积过程的开始提供了了⼀一些线索。

这⾥里里的差异可能会给正在进⾏行行的异域性物种的形成提供证据。

托福阅读TPO31第2篇
Early Children Education
Preschools—educational programs for children under the age of five—differ significantly from one country to another according to the views that different societies hold regarding the purpose of early childhood education. For instance, in a cross-country comparison of preschools in China, Japan, and the United States, researchers found that parents in the three countries view the purpose of preschools very differently. Whereas parents in China tend to see preschools primarily as a way of giving children a good start academically, Japanese parents view them primarily as a way of giving children the opportunity to be members of a group. In the United States, in comparison, parents regard the primary purpose of preschools as making children more independent and self-reliant, although obtaining a good academic start and having group experience are also important.
由于不不同社会持有的关于⼉儿童早教⽬目的观点的不不同，学前班(5岁以下⼉儿童的教育项⽬目)的形式在不不同国家也⼤大不不相同。

⽐比如说，在⼀一项中、⽇日、美三国的跨国学前班调査中，调査者发现这三个国家的⽗父⺟母对学前教育的看法⼤大相径庭。

中国的⽗父⺟母⼤大都认为上学前班可以帮孩⼦子们打开学术上的⼤大⻔门，⽇日本⽗父⺟母则把其看做是⼀一个使孩⼦子融⼊入集体的好机会。

相⽐比之下，美国⽗父⺟母认为学前班最主要的⽬目的是让孩⼦子减少依赖性并变得更更加⾃自⽴立，尽管获得⼀一个良好的学业开端和团队经验同样重要。

While many programs designed for preschoolers focus primarily on social and emotional factors, some are geared mainly toward promoting cognitive gains and preparing preschoolers for the formal instruction they will experience when they start kindergarten. In the United Stated, the best-known program designed to promote future academic success is Head Start. Established in the 1960s when the United States declared the War on Poverty, the program has served over 13 million children and their families. The program, which stresses parental involvement, was designed to serve the “whole child”,
including children’s physical health, self-confidence, social responsibility, and social and emotional development.
许多为学龄前⼉儿童设计的课程项⽬目主要集中在社会因素和情感因素上，⽽而有些主要是为提升学龄前孩⼦子们的认知能⼒力力和给他们提供开始上幼⼉儿园后会经历的正规指导。

在美国，众所周知，为促进未来学术成功设计的项⽬目叫“Head Start”，在20世纪60年年代美国开始“对贫穷开战”时建⽴立的。

这个项⽬目已经为超过13000000孩⼦子和其家庭提供服务。

其强调的是家⻓长的参与，为培养“全⽅方位发展的⼉儿童”所设计的，包括孩⼦子的身体健康、⾃自信⼼心、社会责任感以及社交能⼒力力与情感的发展。

Whether Head Start is seen as successful or not depends on the lens through which one is looking. If, for instance, the program is expected to provide long-term increases in IQ (intelligence quotient) scores, it is a disappointment. Although graduates of Head Start programs tend to show immediate IQ gains, these increases do lot last. On the other hand, it is clear that Head Start is meeting its goal of getting preschoolers ready for school. Preschoolers who participate in Head Start are better prepared for future schooling than those who do not. Furthermore, graduates of Head Start programs have better future school grade. Finally, some research suggests that ultimately Head Start graduates show higher academic performance at the end of high school, although the gains are modest.
“Head Start”的成功与否取决于⼈人们看待的⻆角度。

⽐比如说，如果⼈人们希望它可以带来智商的⻓长期増⻓长，那它终将是令⼈人失望。

因为，尽管“Head Start”可以使智⼒力力迅速地提⾼高，但这种増⻓长并不不会持续太久。

另⼀一⽅方⾯面，很显然，“Head Start”的⽬目标是让学龄前⼉儿童做好上学的准备。

相对那些没参与过“Head Start”计划的孩⼦子们⽽而⾔言，参加了了这个项⽬目的孩⼦子们对学业有着更更充分的准备。

⽽而且，“Head Start”的毕业⽣生今后的学习成绩会更更好。

最后，调査表明，虽然收获⼀一般，但最终“Head Start”的毕业⽣生在⾼高中结束时会取得更更⾼高的学术成就。

In addition, results from other types of preschool readiness programs indicate that those who participate and graduate are less like to repeat grades, and they are more like to complete school than readiness program, for every dollar spent on the program, taxpayers saved seven dollars by the time the graduated reached the age of 27.
此外，从其他类型的学龄前预备项⽬目的结果来看，那些参加过学前项⽬目的毕业⽣生很少重读，他们更更愿意完成学校⽽而不不是预备项⽬目。

在毕业⽣生⻓长到27岁时，纳税⼈人在这个项⽬目上曾经花费的每1美元都可省下7美元。

The most recent comprehensive evaluation of early intervention programs suggests that, taken as a group, preschool programs can provide significant benefits, and that government funds invested early in life may ultimately lead to a reduction in future costs. For instance, compared with children who did not participate in early intervention programs, participants in various programs showed gains in emotional or cognitive development, better educational outcomes, increased economic self-sufficiency, reduced levels of criminal activity, and improved health-related behaviors. Of course, not every program produced all these benefits, and not every child benefited to the same extent. Furthermore, some researchers argue that less-expensive programs are just as good as
relatively expensive ones, such as Head Start. Still, the results of the evaluation were promising, suggesting that the potential benefits of early intervention can be substantial. 最近关于早期介⼊入项⽬目的综合评估表明，总的来说，学前项⽬目可以带来巨⼤大的收益，政府在早期投⼊入的资⾦金金最终会减少未来的花销。

⽐比如说，与没有参与早期介⼊入项⽬目的孩⼦子相⽐比, 参加了了各种项⽬目的孩⼦子在情感和认知能⼒力力上得到了了提⾼高，改善了了教育成果，提⾼高了了经济的⾃自⾜足性，减少了了犯罪⾏行行为的发⽣生，健康⾏行行为得到了了改进。

当然，不不是所有的项⽬目都能产⽣生这样的收益，也不不是每个孩⼦子都能得到同等程度的提⾼高。

此外，⼀一些调査者称那些相对便便宜的项⽬目和昂贵项⽬目结果⼀一样好。

评估的结果仍然很乐观，它认为早期介⼊入的潜在好处是不不可估量量的。

Not everyone agrees that programs that seek to enhance academic skills during the preschool years are a good thing. In fact, according to developmental psychologist David Elkind, United States society tends to push children so rapidly that they begin to feel stress and pressure at a young age. Elkind argues that academic success is largely dependent upon factors out of parents’ control, such as inherited abilities and a child’s rate of maturation. Consequently, children of a particular age cannot be expected to master educational material without taking into account their current level of cognitive development. In short, children require development appropriate educational practice, which is education that is based on both typical development and the unique characteristics of a given child.
并不不是所有⼈人都认为在学前期追求学术上的提⾼高是⼀一件好事。

事实上，据发展⼼心理理学家⼤大卫??艾尔凯德所说，美国社会急于催促逼迫孩⼦子，以⾄至于他们年年纪⼩小却感到压⼒力力。

艾尔凯德认为学术上的成功主要取决于⽗父⺟母控制以外的因素，如天⽣生的能⼒力力和孩⼦子的成熟程度。

因此，如果不不考虑特定年年龄段孩⼦子们⽬目前的认知发展⽔水平，就不不能期待他们掌握教材。

总之，孩⼦子们需要发展适当的教育实践，那就是基于孩⼦子的典型发展和独特性的教育。

托福阅读TPO31第3篇
Savanna Formation
Located in tropical area at low altitudes, savannas are stable ecosystems, some wet and some dry consisting of vast grasslands with scattered tree or shrubs. They occur on a wide range of soil type sand in extremes of climate. There is no simple or single factor that determines if a given site will be a savanna, but some factors seem to play important roles in their formation.
热带草原或热带稀树草原位于热带低海海拔地区，⼲干湿⽓气候皆有。

稀疏分布着树⽊木和灌⽊木的⼴广阔⼤大草原，其为⼀一个稳定的⽣生态系统。

⽓气候极端，涵盖了了⼴广泛的⼟土壤种类。

对于热带草原的形成原因，虽⽆无单⼀一的解释，但似乎仍有⼀一些因素对其形成起到了了重⼤大作⽤用。

Savannas typically experience a rather prolonged dry season. One theory behind savanna formation is that wet forest species are unable to withstand the dry season, and thus savanna, rather than rain forest, is favored on the site. Savannas experience an annual rainfall of between 1000 and 2000 millimeters, most of it falling in a five-to-eight month
wet season.Though plenty of rain may fall on a savanna during the year, for at least part of the year little does, creating the drought stress ultimately favoring grasses. Such conditions prevail throughout much of northern South America and Cuba, but many Central American savannas as well as coastal areas of Brazil and the island of Trinidad do not fit this pattern. In these areas, rainfall per month exceeds that in the above definition, so other factors must contribute to savanna formation.
热带草原通常会经历⼗十分漫⻓长的旱季。

热带草原形成理理论之⼀一，就是湿润的森⽊木物种⽆无法承受⼲干燥的季节——这更更有利利于热带草原，⽽而不不是热带⾬雨林林的形成。

热带草原的年年降⽔水量量在1000到2000毫⽶米，绝⼤大多数降⽔水都集中在⻓长达5到8个⽉月的⾬雨季中。

虽然每年年的降⽔水总量量充⾜足，但⾄至少会有⼏几个⽉月⼏几乎零降⽔水，由此引起的⼲干旱使得该地区最终只适合草地⽣生⻓长。

这样的条件⼴广泛地分布于南美北北部和古巴的⼤大部分地区，但也有例例外，⽐比如在中美洲的稀树⼤大草原，巴⻄西的沿海海地区和特⽴立尼达岛⽓气候的类型就不不⼀一样。

在这些地区每⽉月的降⽔水量量超过了了之前定义的降⽔水量量范围，因此还有其他因素影响着热带草原的形成。

In many characteristics, savanna soils are similar to those of some rain forests, though more extreme. For example, savanna soils, like many rain forest soils, are typically oxisols(dominated by certain oxide minerals) and ultisols (soils containing no calcium carbonate),with a high acidity notably low concentrations of such minerals as phosphorus, calcium, magnesium, and potassium, while aluminum levels are high. Some savannas occur on wet, waterlogged soils; other dry, sandy, well-drained soils. This many seem contradictory, but it only means that extreme soil conditions, either too wet or too dry for forests, are satisfactory for savannas. More moderate conditions support moist forests.
虽然极端，但在⼤大多数特点上，热带草原和⾬雨林林的⼟土壤还是相似的。

⽐比如说，和许多热带⾬雨林林⼟土壤⼀一样，热带草原的⼟土壤通常为含酸量量⾼高的氧化⼟土(某些氧化物矿物占主导)和⽼老老成⼟土(这些⼟土壤中不不含碳酸钙，磷、钙、镁、钾这样的矿物质含量量⾮非常低，⽽而铝的含量量却很⾼高)。

有些热带草原的⼟土壤潮湿，呈溃⽔水状态;⽽而有些的⼟土壤却⼲干燥、多沙、易易排⽔水。

这看起来⽭矛盾，但却意味着只有像过度湿润或过度⼲干旱那样的极端⼟土壤条件，才适合热带草原，温润的⽓气候适合湿润的森林林。

Waterlogged soils occur in areas that are flat or have poor drainage. These soils usually contain large amounts of clay and easily become water-saturated. Air cannot penetrate between the soil particles, making the soil oxygen-poor. By contrast, dry soils are sandy and porous, their coarse textures permitting water to drain rapidly. Sandy soils are prone to the leaching of nutrients and minerals and so tend to be nutritionally poor. Though most savannas are found on sites with poor soils (because of either moisture conditions or nutrient levels of both), poor soils can and do support lush rain forest.
溃⽔水⼟土壤出现在地形平坦和排⽔水性差的地⽅方。

这些⼟土壤通常含有⼤大量量的黏⼟土，这就会使它们很容易易处于饱⽔水状态。

由于空⽓气不不能渗⼊入⼟土壤颗粒中，⼟土壤的含氧量量就低。

与之相对，⼲干燥⼟土壤是多沙和多孔渗⽔水的。

它们的粗质结构可以让⽔水很快排⼲干。

砂质⼟土壤更更易易于营养物和矿
物质的过滤渗漏漏，这就导致⼟土壤缺乏营养。

虽然⼤大多数热带草原都位于贫瘠⼟土壤区(⽆无论是因为各⾃自的⽔水分条件还是营养等级)，但贫瘠⼟土壤也的确能够⻓长出繁茂的热带⾬雨林林。

Most savannas probably experience mild fires frequently and major burns every two years or so. Many savanna and dry-forest plant species are called pyrophytes, meaning they are adapted in various ways to withstand occasional burning. Frequent fire is a factor to which rain forest species seem unable to adapt, although ancient charcoal remains from Amazon forest soils dating prior to the arrival of humans suggest that moist forests also occasionally burn. Experiments suggest that if fire did not occur in savannas in the Americas, species composition would change significantly. When burning occurs, it prevents competition among plant species from progressing to the point where some species exclude others, reducing the overall diversity of the ecosystem. But in experimental areas protected from fire, a few perennial grass species eventually come to dominate, outcompeting all others.Evidence from other studies suggests that exclusion of fire results in markedly decreased plant-species richness, often with an increase in tree density. There is generally little doubt that fire is a significant factor in maintaining savanna, certainly in most regions.
⼤大多数热带草原都可能经历着频繁的焚烧，⽽而⼤大约两年年就有⼀一次⼤大⽕火燃烧。

许多热带草原和⼲干燥林林的植物种类被叫做耐⽕火植物，意思是其善于⽤用各种⽅方法来抵御偶尔发⽣生的燃烧。

虽然追溯到⼈人类初⾄至时亚⻢马逊森林林⼟土壤中遗留留的古⽊木碳表明湿润林林带也会有不不定期的燃烧，但频繁的⼤大⽕火还是热带⾬雨林林物种所不不能适应的因素。

实验表明，如果美国的热带草原没有发⽣生⼤大⽕火，物种的构成就会变得完全不不⼀一样。

焚烧的防⽌止了了植物之间的竞争，这就避免了了因植物间的排挤⽽而使整个⽣生态系统的多样性发⽣生变化。

但是在防⽕火实验区，⼀一些多年年⽣生植物物种最终占得主导地位，胜过了了其他物种。

其他调査证据表明，没有焚烧则导致植物物种丰富性的显著减少，通常还会伴随着树的密度増加。

这就可以确定，⽕火是维持热带草原的重要因素。

当然，这指的是在⼤大多数地区。

【6】On certain sites, particularly in South America, savanna formation seems related to frequent cutting and burning of moist forests for pastureland. Increase in pastureland and subsequent overgrazing have resulted in an expansion of savanna. The thin upper layer of humus (decayed organic matter) is destroyed by cutting and burning. Humus is necessary for rapid decomposition of leaves by bacteria and fungi and for recycling by surface roots. Once the humus layer disappears, nutrients cannot be recycled and leach from the soil, converting soil from fertile to infertile and making it suitable only for savanna vegetation. Forests on white, sandy soil are most susceptible to permanent alteration.
在某些地区，特别是在南美洲，热带草原的形成可能和为了了建造牧场⽽而对湿润林林地进⾏行行频繁的砍伐和焚烧有关。

牧场的増加和随之⽽而来的过度放牧导致了了热带草原的扩张。

稀薄的腐殖质(腐烂的有机物)上层被砍伐和焚烧⾏行行为所破坏。

腐殖质是树叶被细菌和真菌迅速分解和根部表⾯面循环的必需品。

⼀一旦腐⾯面层消失了了，营养物质便便不不能循环并渗⼊入⼟土壤中，⼟土壤由肥沃变得贫瘠，这就使它只适合热带草原植被的⽣生⻓长。

⽩白⼟土和砂⼟土上的森林林结构容易易发⽣生永久性的改变。

托福阅读TPO32第1篇
Plant Colonization
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.
殖⺠民化是植物能够改变⼀一个地⽅方⽣生态的⼀一种⽅方法。

这是⼀一个由两部分组成的过程：⼊入侵和⽣生存。

⼀一个地⽅方被植物殖⺠民的⽐比率是取决于两个东⻄西的速率：⽣生物体(种⼦子，孢⼦子，成熟或不不成熟的个体) 到达这个区域和它们能成功地⽴立⾜足和⽣生存。

成功的殖⺠民化取决于有⼀一个⾮非常适合定居的场所——所谓安全的地⽅方就是，⽕火灾和砍伐的⼲干扰已经赶⾛走了了竞争物种或已经减⼩小了了竞争⼒力力和对⼊入侵物种要⽴立⾜足产⽣生的阻⼒力力。

对于⼊入侵速率，迁居到⼀一个潮湿肥沃的地⽅方会⽐比到⼀一个⼲干的，不不肥沃的地⽅方更更快，因为在后者更更难存活。

⼀一个肥沃，翻耕的领域会迅速地被⼤大量量多样的野草侵⼊入，然⽽而⼀一个邻近的建筑区，为了了曝光⼀一个粗糙不不肥沃的，并且⼏几乎可能是多⽉月或多年年都没有植被覆盖的⺟母质层，它的⼟土壤已经是被压实或是移动，尽管是收到了了如在翻耕区域相同的种⼦子投⼊入。

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).
在不不同的植物种类中，⼊入侵率和灭绝率有很⼤大的差别。

先驱物种——只出现在殖⺠民的最初阶段——它们能⾼高效的⼊入侵，因为它们可以产⽣生⼤大量量的⽣生殖繁殖体 (像是种⼦子，孢⼦子之类) 并且它们有⼀一种⾼高效的传播⽅方式 (正常情况下，是⻛风) 。

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.
如果殖⺠民植物产出的是寿命较短的⽣生命繁殖体，之后它们就必须繁殖很⼤大的数量量，除⾮非它们有⼀一种⾼高效的传播⽅方式去适应新的栖息地。

很多植物依靠⻛风去传播并且产⽣生⼤大量量的⼩小且寿命相对较短的种⼦子来抵消这样⼀一种⻛风并不不总是能可靠地到达⼀一个适合的栖息地的事实。

⼀一些植物已经发展了了可供选择的策略略，像那些能⽣生产出通过⻦鸟或⼩小型哺乳动物带到合适栖息地的较⼩小却更更⼤大的种⼦子的植物，或是能⽣生产出存活得更更久的种⼦子的植物。

很多的森林林植物偏于选择第⼆二种⽅方法，并且⼤大量量先驱植物的可存活种⼦子也能在森林林地被物上被找到。

举个例例⼦子，在不不列列颠哥伦⽐比亚沿海海的道格拉斯⻄西部铁杉森林林⾥里里，每⼀一平⽅方⽶米都能找到1125 个可⽣生⻓长的种⼦子。

⼏几乎所有在这个种⼦子库⾥里里发芽的种⼦子都是属于先驱植物。

如这样快速的在这种已被⼲干扰的区域殖⺠民毫⽆无疑问是在部分反映出这个⾬雨林林地表的种⼦子库。

【4】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.
这种在殖⺠民物种⾥里里发展的很好的适应⽅方法在萌芽期(种⼦子成⻓长初期)中存在很⼤大程度的变化。

⼀一个特定物种的种⼦子表现出⼀一个较宽范围的发芽期，这增加了了⾄至少有⼀一部分种⼦子会在有良好的环境条件时期发芽的可能性。

这对于要迁居到没有植被去改善极端⽓气候和已具备⽓气候多样性的地⽅方的物种尤其重要。

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.
植物群落⾥里里的物种演替，意思就是说，物种出现和消失的时间顺序是依赖于在⼀一个物种的⽣生存史中发⽣生在不不同阶段的事件。

⼊入侵和⽣生⻓长⽐比率的变化在决定演替模式中扮演着⼀一个重要⻆角⾊色，尤其是在次级演替中。

⾸首先迁居到别处的物种都可以产出⼤大量量能够顺利利分散到新地点的。