托福阅读理解的一大要点就是逻辑理解，逻辑理解一方面是指对于文章中的逻辑关联词的把握；另一方面也包括对于文章整体逻辑思路的把握。从一篇托福阅读文章出发，为大家解读托福阅读逻辑的重要性。(文章来源TPO29)

　　注：重要逻辑词用紫色标出，重点信息加粗标识。

　　When several individuals of the same species or of several different species depend on the same limited resource, a situation may arise that is referred to as competition. (给出竞争的定义)The existence of competition has been long known to naturalists; its effects were described by Darwin in considerable detail. Competition among individuals of the same species (intraspecies competition), one of the major mechanisms of natural selection, is the concern of evolutionary biology. Competition among the individuals of different species (interspecies competition) is a major concern of ecology. It is one of the factors controlling the size of competing populations, and extreme cases it may lead to the extinction of one of the competing species. This was described by Darwin for indigenous New Zealand species of animals and plants, which died out when competing species from Europe were introduced.(种群内部竞争和种群外部竞争各自的定义)

　　No serious competition exists when the major needed resource is in superabundant supply, as in most cases of the coexistence of herbivores (plant eaters). (主题句：必要资源充足的情况下不存在激烈竞争)Furthermore, most species do not depend entirely on a single resource, if the major resource for a species becomes scarce, the species can usually shift to alternative resources. If more than one species is competing for a scarce resource, the competing species usually switch to different alternative resources. (Furthermore作为逻辑词提示考生可以先略过其后面的句子内容，大概了解后面是关于资源竞争的一个事实说明就好，if引起对上一句的进一步说明)Competition is usually most severe among close relatives with similar demands on the environment. But it may also occur among totally unrelated forms that compete for the same resource, such as seed-eating rodents and ants. (近亲之间的竞争往往最激烈，这一点也是主题之下的一个说明)The effects of such competition are graphically demonstrated when all the animals or all the plants in an ecosystem come into competition, as happened 2 million years ago at the end of Pliocene, when North and South America became joined by the Isthmus of Panama. North and South American species migrating across the Isthmus now came into competition with each other. The result was the extermination of a large fraction of the South American mammals, which were apparently unable to withstand the competition from invading North American species—although added predation was also an important factor.(as引起例子，在扫读时可以略过先不看)

　　段落分析：段落主旨是必要资源充足的情况下不存在激烈竞争。然后说明近亲之间由于环境资源需求相似存在激烈竞争、不相关但需要统一资源物种之间存在激烈竞争、一个生态系统中的所有动植物都参与到竞争中来时竞争激烈。段落中的并列逻辑词 furthermore；举例逻辑词 such as 、as；条件逻辑词If 等都可以帮助考生串联内容。

　　To what extent competition determines the composition of a community and the density of particular species has been the source of considerable controversy. (主题句：竞争在多大程度上决定特定群落组成和特定物种密度引起争议)The problem is that competition ordinarily cannot be observed directly but must be inferred from the spread or increase of one species and the concurrent reduction or disappearance of another species. (进一步解释争议的问题具体是什么)The Russian biologist G. F. Gause performed numerous two-species experiments in the laboratory, in which one of the species became extinct when only a single kind of resource was available. On the basis of these experiments and of field observations, the so-called law of competitive exclusion was formulated, according to which no two species can occupy the same niche. (俄罗斯生物学家的试验和结论：竞争灭绝法则是成立的)Numerous seeming exceptions to this law have since been found, but they can usually be explained as cases in which the two species, even though competing for a major joint resource, did not really occupy exactly the same niche.(说明实验结论例外情况的原因)

　　段落分析：本段结构较为简单，主题句+进一步解释+例子：实验及结论。

　　Competition among species is of considerable evolutionary importance. (物种间的竞争机制对进化过程很重要)The physical structure of species competing for resources in the same ecological niche tends to gradually evolve in ways that allow them to occupy different niches. Competing species also tend to change their ranges so that their territories no longer overlap. (两种进化的方向：依赖的资源变化和生活区域)The evolutionary effect of competition on species has been referred to as “species selection”; however, this description is potentially misleading. Only the individuals of a species are subject to the pressures of natural selection. The effect on the well-being and existence of a species is just the result of the effects of selection on all the individuals of the species. Thus species selection is actually a result of individual selection.

　　段落分析：本段中的并列逻辑词also、转折逻辑词 however与结论逻辑词Thus给出了段落的清晰结构：竞争对进化的2种影响结果+“species selection”概念的讨论(其中包含了一个thus引导的结论)

　　Competition may occur for any needed resource. (任何必须的资源都可能引发竞争)In the case of animals it is usually food; in the case of forest plants it may be light; in the case of substrate inhabitants it may be space, as in many shallow-water bottom-dwelling marine organisms. (几个举例)Indeed, it may be for any of the factors, physical as well as biotic, that are essential for organisms. (表示确定的逻辑词Indeed)Competition is usually the more severe the denser the population. Together with predation, it is the most important density-dependent factor in regulating population growth.

　　以上就是为大家带来的托福阅读文章分析，可见在托福阅读中逻辑词是很重要的，考生可以根据逻辑词来判断内容的重要程度，也可以利用逻辑词理清文章思路。在文章后托福阅读题目中也有不少题目和逻辑词相关，大家可以找到本文TPO题目进行练习。

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