2016年2月27日托福阅读解析

　  2月27日托福阅读第一篇

　　题材划分：动物类

　　主要内容：动物灭绝

　　讲的是大型动物的灭绝。第一题问哪里的动物灭绝率高。文章讲到两个可能的因素。第一点说可能是因为气候的变化，但是有反驳说不对，动物都能迁徙到适合的地方，但事实是有些动物没走。举了一个例子，这里也有题。第二点说可 能是人类的捕杀，但是有证据表明人类比较少，居住也很分散，而且大多证据都是小型动物，没有大型动物。也举了个例子，是澳大利亚，也有题。然后这段末尾有个词汇题。最后一段总结概括说其实可能两种因素都有，需综合考虑，可能是共同作用的结果。

　　相似TPO练习推荐：

　　Official Model Exam-Meteorite Impact and Dinosaur Extinction

　　TPO-8 Extinction of the Dinosaurs

　　TPO-15 Mass Extinctions

　　相关背景知识：

　　Habitat degradation is currently the main anthropogenic cause of species extinctions. The main cause of habitat degradation worldwide is agriculture, with urban sprawl, logging, mining and some fishing practices close behind. The degradation of a species' habitat may alter the fitness landscape to such an extent that the species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic, or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species.

　　Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness.

　　Habitat degradation can also take the form of a physical destruction of niche habitats. The widespread destruction of tropical rainforests and replacement with open pastureland is widely cited as an example of this; elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive without forest to shelter it. Another example is the destruction of ocean floors by bottom trawling.

　　Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing unwelcome competition to other species that previously occupied that area. Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources. Vital resources including water and food can also be limited during habitat degradation, leading to extinction.

　　There have been at least five mass extinctions in the history of life on earth, and four in the last 350 million years in which many species have disappeared in a relatively short period of geological time. A massive eruptive event is considered to be one likely cause of the "Permian–Triassic extinction event" about 250 million years ago, which is estimated to have killed 90% of species then existing. There is also evidence to suggest that this event was preceded by another mass extinction, known as Olson's Extinction. The Cretaceous–Paleogene extinction event occurred 66 million years ago, at the end of the Cretaceous period, and is best known for having wiped out non-avian dinosaurs, among many other species.

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