托福阅读真题+题目+答案：Foundational and Keystone Species

托福阅读真题+题目+答案：Foundational and Keystone Species

The harmony present in any ecological system relies on the inclusion of different types of species, each with a specific role or set of roles. Although to some extent all species contribute in important ways, scientists are now learning about the pivotal parts played by, what are being called foundational and keystone species. Interestingly, the latter represent only a small fraction of the overall animal population within an ecosystem while the former can make up a significant portion of it. In both cases, though, their removal often results in massive changes to, if not the complete destruction of, their ecosystems. Efforts to conserve these species are currently based on the new idea that they prevent the start of a domino effect that would, once started, be unstoppable.

Foundational species are the backbones of the systems they inhabit. These species are referred to as primary producers, which means that they generate a large amount of the abundance other species require to survive. In most cases, they are a type of vegetation or stationary animal. Coral, which tends to grow in large colonies, is often pointed to as an example. Eventually a group of colonies will form a coral reef, which can sustain a complete ecosystem around it. The reef contains the skeletal remains of coral at its bottom and living coral on the top. Numerous animals, including zooplankton and sponges, live in the small crevices located in the rock-like bottom. At the top, the coral interacts with seaweed and other forms of vegetation to regulate the levels of nutrients and gases in the water. There are also more than four thousand types of fish that live on or around most coral reefs. Fish rely on the holes in the reef for protection. The more colorful species of coral provide excellent camouflage for fish, as well. Obviously, without its foundational species, an ecosystem would collapse.

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托福阅读真题题目：

1. The word extent in the passage is closest in meaning to

(A) amount

(B) explanation

(C) purpose

(D) average

2. According to paragraph 1, foundational species are usually

(A) responsible for environmental damage

(B) present only in certain ecosystems

(C) close to complete extinction

(D) found in the largest number

3. The word sustain in the passage could best be replaced by

(A) endure

(B) create

(C) receive

(D) support

4. The word it in the passage refers to

(A) coral

(B) coral reef

(C) ecosystem

(D) colony

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