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题型:阅读理解-阅读单选 难度:0.65 引用次数:104 题号:22027608

Different forests in the western United States have unique combinations of trees and birds. One type has broad-leaved trees like ash and cottonwood, along with kingbirds. Anoher type has evergreen trees like pine and white spruce, along with juncos. Ecologists in the early twentieth century once claimed these ecological communities were precisely balanced systems, where every species had a specific role to play in a complex machine. They believed that removing or adding any plant, bird, or insect, could disrupt this balance and harm the habitat. One of these pioneer ecologists was Frederick Clements, who believed that in a specific climate area, ecological communities gradually moved toward the most balanced and integrated group of species in that region.

Clements was challenged by another pioneer ecologist, Henry Gleason, who took the opposite view. Gleason viewed the community as largely a group of species with similar tolerances to the stresses given by climate and other factors typical of the region. Gleason thought chance played a big role in where species lived. His concept suggests that nature is not highly integrated. Each species is responding individually to its surroundings. Gleason thought things could change in different ways, depending upon local conditions.

Who was right? It now appears that Gleason was more accurate than Clements. The ecological community is mostly a random collection of species with similar responses to a particular climate. Ash trees are found in association with cottonwood trees because both can survive well on floodplains and the competition between them is not so strong that only one can survive.

This is not to say that precise harmonies are not present within communities. Most flowering plants rely on pollinators (传粉者). But if we see a precise balance of nature, it is largely a product of our perception, due to the false belief that nature, especially a complex system like a forest, seems so unchanging from one day to the next.

1. Early 20th century ecologists commonly claimed that___________.
A.each species plays a specific role in the community
B.new species need to be added as communities develop
C.maintaining precise balance in community is challenging
D.it is important to protect communities by removing certain species
2. According to Gleason, what influences where species live?
A.How individualistic the species is.B.Their ability to tolerate the stresses there.
C.The number of similar species present.D.Their ways to integrate with other species.
3. Why does the author mention two kinds of trees in paragraph 3?
A.To show greater species variety in floodplains.
B.To provide evidence to support Clements’ theory.
C.To give an example of species that prefer to live on floodplains.
D.To support the current view on how ecological communities develop.
4. The underlined word “perception” in paragraph 4 is closest in meaning to____________.
A.cultureB.environmentC.understandingD.education
【知识点】 科普知识 说明文

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