When several individuals of the samespeciesor of several differentspeciesdependon the same limitedresource, a situation may arise that is referred to as competition. Theexistenceof competition has been long known to naturalists; its effects were described by Darwin inconsiderabledetail. Competition among individuals of the samespecies(intraspecies competition), one of themajormechanisms of naturalselection, is theconcernofevolutionarybiology. Competition among the individuals of differentspecies(interspecies competition) is amajorconcernofecology. It is one of the factors controlling the size ofcompetingpopulations, andextremecases it mayleadto theextinctionof one of thecompetingspecies. This was described by Darwin forindigenousNew Zealandspeciesof animals and plants, which died out whencompetingspeciesfrom Europe were introduced.

No serious competition exists when themajorneededresourceis in superabundantsupply, as in most cases of the coexistence of herbivores (plant eaters). Furthermore, mostspeciesdo notdependentirelyon a singleresource, if themajorresourcefor aspeciesbecomesscarce, thespeciescan usuallyshifttoalternativeresources. If more than onespeciesiscompetingfor ascarceresource, thecompetingspeciesusuallyswitchto differentalternativeresources. Competition is usually mostsevereamong close relatives withsimilardemands on the environment. But it may alsooccuramong totally unrelated forms thatcompetefor the sameresource, such as seed-eating rodents and ants. The effects of such competition are graphically demonstrated when all the animals or all the plants in anecosystemcome 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 Americanspeciesmigratingacrossthe Isthmus now came into competition with each other. The result was the extermination of a largefractionof the South American mammals, which were apparently unable towithstandthe competition from invading North American species----although addedpredationwas also an importantfactor.

To whatextentcompetition determines thecompositionof acommunityand thedensityofparticularspecieshas been thesourceofconsiderablecontroversy. The problem is that competition ordinarily cannot be observed directly but must be inferred from thespreador increase of onespeciesand the concurrentreductionor disappearance of anotherspecies. The Russian biologist G. F. Gause performednumeroustwo-species experiments in thelaboratory, in which one of thespeciesbecameextinctwhen only a single kind ofresourcewasavailable. On the basis of these experiments and offieldobservations, theso-calledlaw ofcompetitiveexclusion was formulated, according to which no twospeciescanoccupythe sameniche. Numerousseeming exceptions to this law have since been found, but they can usually be explained as cases in which the twospecies,eventhoughcompetingfor amajorjointresource, did not reallyoccupyexactly the sameniche.

Competition amongspeciesis ofconsiderableevolutionaryimportance. Thephysicalstructure ofspeciescompetingfor resources in the sameecologicalnichetends tograduallyevolvein ways that allow them tooccupydifferent niches. Competingspeciesalsotendto change their ranges so that their territories no longeroverlap. Theevolutionaryeffect of competition onspecieshas been referred to as “speciesselection”; however, this description is potentially misleading. Only the individuals of aspeciesaresubjectto the pressures of naturalselection. The effect on the well-being andexistenceof aspeciesis just the result of the effects ofselectionon all the individuals of thespecies. Thusspeciesselectionis actually a result ofindividualselection.

Competition mayoccurfor any neededresource.

In the case of animals it is usually food; in the case of forest plants it may be light; in the case ofsubstrateinhabitants it may bespace,

as in many shallow-water bottom-dwellingmarineorganisms. Indeed, it may be for any of the factors,physicalas well as biotic, that areessentialfor organisms. Competition is usually the moreseverethe denser the population. Together withpredation, it is the most important density-dependentfactorin regulating population growth.

Questions:
question_stem: The phrase “mechanisms of natural selection”in the passage is closest in meaning to
choices: tag: A
text: types of natural selection

tag: B
text: dangers of natural selection

tag: C
text: problems natural selection solves

tag: D
text: ways natural selection works
answer_key: D
explanation: D mechanism: 机制，途径。对应 D 选项的 ways（方法，途径）。对应原文： Competition among individuals of the same species (intraspecies competition), one of the major mechanisms of natural selection, is the concern of evolutionary biology 从原文也可以推断出来。我们都知道进化是由于“物竞天择”的原因，原文这一句就是这个意思。而 mechanisms of natural selection 出现在插入语成分当中，主要用来修饰 competition,说 competition 是一种自然选择的 mechanism。B 选项的 dangers 和 C 选项的 problems 明显不对，而 A 和 D 之间，D 更接近 mechanism 的意思，因此这道题选择 D。

question_stem: According to paragraph 1, what is one effect of competition among individuals of different species?
choices: tag: A
text: It results in the eventual elimination of the resource for which they are competing.

tag: B
text: It leads to competition among individuals of the same species.

tag: C
text: It encourages new species to immigrate to an area.

tag: D
text: It controls the number of individuals in the competing populations.
answer_key: D
explanation: D 用 different species 定位到原文倒数第二、三句话： 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.这里明确说了，这是对于竞争种群的一种控制，极端情况下可能会使其中一个竞争物种灭绝。所以，对应 D 选项的 control。ABC 选项都没有提及。

question_stem: The word “indigenous”in the passage is closest in meaning to
choices: tag: A
text: native

tag: B
text: rate

tag: C
text: most

tag: D
text: numerous
answer_key: A
explanation: A Indigenous: 本土的。对应 A 选项的 native（本土的）。B 是稀少的，C 是大部分的，D 是无数的。对应原文 This was described by Darwin for indigenous New Zealand species of animals and plants, which dies out when competing species from Europe were introduced.这个词义也可以从原文推断。原文最后半句，which 引导的从句说由于欧洲引进的种族和 which 指代的 indigenous 的新西兰物种竞争，是 indigenous 的新西兰物种灭绝了。这两个物种呈现竞争对立的关系，用这层关系可以进行推测。A 选项带入最合适。

question_stem: In paragraph 1, why does the author mention what happened in New Zealand?
choices: tag: A
text: To indicate that Darwin understood the importance of competition

tag: B
text: To illustrate that competition can lead to the extinction of species

tag: C
text: To identify where the idea of competition among species first arose

tag: D
text: To argue against the idea that the process of selection is a natural occurrence
answer_key: B
explanation: B 先用 New Zealand 定位到细节出处，即该段的最后一句话，这句话说由于欧洲引进的种族和本土的新西兰物种竞争，使本土的新西兰物种灭绝了。往前寻找要支撑的观点句，前一二句话说到种族间竞争时的论点是可以控制不同种族的数量。然后举出了新西兰动植物作为了例子，而例子都是用来证明和支持观点的。因此选择 B 选项。

question_stem: According to paragraph 2, competition is not usually a significant factor among two coexisting species when
choices: tag: A
text: one of the species has only recently moved into the territory of the other

tag: B
text: the species are closely related to each other

tag: C
text: the population of one species is much larger than that of the other

tag: D
text: both of the species are herbivores
answer_key: D
explanation: D 根据 coexisting species 定位到第一句话： No serious competition exists when the major needed resources is in superabundant supply, as in most cases of the coexistence of herbivores (plant eaters).这句话中提到了资源供给充足的话，就不会有太多的竞争，大部分的食草动物正式如此。所以对应 D 选项。A 选项和原文由出入，原文是说如果竞争太强，有一个物种可能会转向其他的 resource；B 选项的内容和原文相反，原文说了 closely related 的物种可能会竞争最激烈；C 选项没有提及。

question_stem: The word “graphically”in the passage is closest in meaning to
choices: tag: A
text: vividly

tag: B
text: frequently

tag: C
text: broadly

tag: D
text: typically
answer_key: A
explanation: A graphically: 生动的。对应 A 选项 vividly（生动的）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 the Pliocene,  when North South America became joined by the Isthmus of Panama. Graph 是图画的意思，graphically 也就是用图形地，可以推出生动地的意思。因此选择 A 选项的 vividly。 B 选项是频繁地，C 是广泛地，D 是特别地。都不符合。也可以根据原文的前后搭配，将选项代入，排除明显不合适的的答案。BCD 代入不合适。

question_stem: In paragraph 2, why does the author talk about what happened as a result of North and South America becoming joined at the Isthmus of Panama?
choices: tag: A
text: To make the point that predation can have as much effect on species survival as competition does

tag: B
text: To show how the ability to switch to an alternative resource can give a species a competitive advantage

tag: C
text: To account for the current species composition of North and South America

tag: D
text: To provide an example of the serious effects of competition between unrelated species
answer_key: D
explanation: D 用 Isthmus of Panama 先定位到细节的出处，发现是一个具体的例子的描述。往前去寻找主旨句，定位到 but 引导的句子： But it may also occur among totally unrelated forms that compete for the same resource, such as seed-eating rodents and ants.这句主旨句中说了，完全不相关的物种也可能会竞争同一种资源，他们之间也会产生强烈的竞争。由此推断，南北美洲动物竞争的结果就是为了说明竞争的 Effects。因此选择 D。A 原文提到了，在最后的半句，但是前面的 although 说明了这不是主要观点。

question_stem: Paragraph 3 supports the idea that Gause’s experiments were important because they
choices: tag: A
text: provided a situation in which competition could be removed from the interaction between two species

tag: B
text: showed that previous ideas about the extent to which competition determines the composition of a community were completely mistaken

tag: C
text: helped establish that competition will remove all but one species from any given ecological niche

tag: D
text: offered evidence that competition between species is minimal when there is an overabundance of a single food source
answer_key: C
explanation: C 通过 Gause's experiments 定位，文章在描述完实验内容后，说 on the basis of these experiment，那么说明后面就是实验得到的结论： 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.这里说了没有两个物种可以占有同一个生态位，即：一个 niche 只能有一个物种，和 C 选项吻合。ABD 在原文都没有提及。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Apparent exceptions to this law usually involves cases in which two species compete for the same major resource but occupy slightly different niches.

tag: B
text: Although it may appear that two species always have different niches, many exceptions show that species compete with each other.

tag: C
text: Cases in which two species not only compete for a shared resource but also occupy similar niches are considered exceptions to this law.

tag: D
text: Cases in which the two species do not occupy that same niche yet still compete for the same resource are believed to be exceptions to this law.
answer_key: A
explanation: A 原文中句子的主干是 seeming exceptions have been found，然后存在了转折逻辑之后说这种例外是可以被解释的。因此只有 A 选项将这两个主要的意思包含进去。B 选项的后半句话和原句不符，C 选项的 not only, but also 的并列逻辑明显和原句不符,D 都在一定程度上改变了原句的意思，没有表达出原句的 not exactly the same niche,其逻辑关系变动过大。

question_stem: According to paragraph 4, how does competition affect evolution?
choices: tag: A
text: It results in the evolution of physical structures that allow the species to compete with each other more effectively.

tag: B
text: It results in the evolutionary extinction of all but one of the competing species.

tag: C
text: It results in the competing species evolving in such a way that they no longer compete for the same resources.

tag: D
text: It results in the competing species evolving to become so much like each other that competition between them eventually disappears.
answer_key: C
explanation: C 用 evolution 去定位，定位到第一句，第一句就提到了问题所问的内容，说 competition 具有 evolutionary importance。后面应该就是具体的解释。往后看说同一小生态环境中的竞争物种 tend to….那么 tend to 的内容就是答案： 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.说使得其领地不再重叠，也就是不再同一区域内进行资源竞争了，对应的就是 C。其他三个选项在原文都没有提及。

question_stem: According to paragraph 4, “species selection”is a misleading term because it
choices: tag: A
text: overemphasizes the role of selection pressure in species extinction

tag: B
text: suggests that selection pressures directly influence whole species

tag: C
text: does not make a distinction between species extinction and species evolution

tag: D
text: suggests that extinction always results whenever there is a competition
answer_key: B
explanation: B 通过 species selection 定位到”The evolutionary effect of competition…”，后面出现了转折，说这个描写是 misleading 的。往后肯定就会解释原因： 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.原文说 natural selection 其实是直接作用在 individual 上的，而不是 species 上。所以错误。对应了 B 选项，“species selection 暗示了选择压力是直接作用于整个物种上的。”

question_stem: The word “regulating”in the passage is closest in meaning to
choices: tag: A
text: controlling

tag: B
text: explaining

tag: C
text: observing

tag: D
text: stopping
answer_key: A
explanation: A regulate: 调节，控制。对应 A 选项的 control（控制）对应原文 Together with predation, it is the most important density-dependent factor in regulating population growth.最后一句是说在 regulating 数量增长中，它是最重要的密度依赖的因素。很容易理解是控制。因此选 A。B 是解释，C 是观察，D 是停止。BCD 代入后都不能和 population growth 形成合适的搭配。