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TPO 29—2 Competition
原文：
【1】When veral individuals of the same species or of veral different species depend on the same limited resource, a situation may ari that is referred to as competition. The existence of competition has been long known to naturalists; its effects were described by Darwin in considerable detail. Compe
tition among individuals of the same species (intraspecies competition), one of the major mechanisms of natural lection, 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 cas 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.母猪养殖
【2】No rious competition exists when the major needed resource is in superabundant supply, as in most cas of the coexistence of herbivores (plant eaters). 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. Competition is usually most vere among clo relatives with similar demands on the environment. But it may also occur among totally unrelated forms that compete for
the same resource, such as ed-eating rodents and ants. The effects of such competition are graphically demonstrated when all the animals or all the plants in an ecosystem come into competitio
n, 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.
【3】To what extent competition determines the composition of a community and the density of particular species has been the source of considerable controversy. The problem is that competition ordinarily cannot be obrved directly but must be inferred from the spread or increa of one species and the concurrent reduction or disappearance of another species. The Russian biologist G. F. Gau 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 the experiments and of field obrvations, the so-called law of competitive exclusion was formulated, according to which no two species can occupy the same niche. Numerous eming exceptions to this law have since been found, but they can usually be explained as cas in which the two species, even though competing for a major joint resource, did not really occupy exactly the same niche.
【4】Competition among species is of considerable evolutionary importance. 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. The evolutionary effect of competition on species has been referred to as “species lection”; however, this description is potentially misleading. Only the individuals of a species are subject to the pressures of natural lection. The effect on the well-being and existence of a species is just the result of the effects of lection on all the individuals of the species. Thus species lection is actually a result of individual lection.
【5】Competition may occur for any needed resource. In the ca of animals it is usually food; in the ca of forest plants it may be light; in the ca of substrate inhabitants it may be space, as in many shallow-water bottom-dwelling marine organisms. Indeed, it may be for any of the factors, physical as well as biotic, that are esntial for organisms. Competition is usually the more vere the denr the population. Together with predation, it is the most important density-dependent factor in regulating population growth.
王文格题目：
1.The phra "mechanisms of natural lection" in the passage（paragraph 1）is clost in meaning to
B.dangers of natural lection.
C.problems natural lection solves.
D.ways natural lection works.
牛奶面包2.According to paragraph 1, what is one effect of competition among individuals of different species?
A.It results in the eventual elimination of the resource for which they are competing.
B.It leads to competition among individuals of the same species.
C.It encourages new species to immigrate to an area.
D.It controls the number of individuals in the competing populations.
3.The word "indigenous" in the passage（paragraph 1）is clost in meaning to
A.native.
B.rate.
丁香的作用
小孩百日宴祝福语
D.numerous.
4.In paragraph 1, why does the author mention what happened in New Zealand?鲜豆皮
A.T o indicate that Darwin understood the importance of competition.
1099年
B.To illustrate that competition can lead to the extinction of species.
C.To identify where the idea of competition among species first aro.
D.T o argue against the idea that the process of lection is a natural occurrence.
5.According to paragraph 2, competition is not usually a significant factor among two coexisting species when
< of the species has only recently moved into the territory of the other.
