托福阅读素材:分散分布的优点
2017-10-23编辑: 环球教育整理来自: 环球教育
很多考生会抱怨托福阅读时间不够,还没完全理解文章就做题,正确率不高。其实这是我们对托福阅读素材不熟悉造成的,下面小编整理了一下托福阅读考试最新的素材,希望能帮助大家更加快速高效的备考托福。
托福阅读素材:分散分布的优点
内容回忆:讲诉同种动物的分散分布。有种松鼠,公的爱跑得离家远一点,母的喜欢待在家,因为家里的世袭的资源为母松鼠提供条件,而公的待在家容易近亲交配,生下来的仔活不久,不能生育;獅子也这样,但是公的跑的远的原因是别的公狮子当了老大,原来团体的公狮子就被赶走了。
参考阅读:TPO38-2: The Raccoons's Success
Raccoons have a vast transcontinental distribution, occurring throughout most of North America and Central America. They are found from southern Canada all the way to Panama, as well as on islands near coastal areas. They occur in each of the 49 states of the continental United States. Although raccoons are native only to the Western Hemisphere, they have been successfully transplanted to other parts of the globe.
Following a decline to a relatively low population level in the 1930s, raccoons began to prosper following their 1943 breeding season. A rapid population surge continued throughout the 1940s, and high numbers have been sustained ever since. By the late 1980s, the number of raccoons in North America was estimated to be at least 15 to 20 times the number that existed during the 1930s. By now, their numbers have undoubtedly grown even more, as they have continued to expand into new habitats where they were once either rare or absent, such as sandy prairies, deserts, coastal marshes, and mountains. Their spread throughout the Rocky Mountain West is indicative of the fast pace at which they can exploit new environments. Despite significant numbers being harvested and having suffered occasional declines, typically because of disease, the raccoon has consistently maintained high population levels.
Several factors explain the raccoon's dramatic increase in abundance and distribution. First, their success has been partially attributed to the growth of cities, as they often thrive in suburban and even urban settings. Furthermore, they have been deliberately introduced throughout the continent. Within the United States, they are commonly taken from one area to another, both legally and illegally, to restock hunting areas and, presumably, because people simply want them to be part of their local fauna. Their appearance and subsequent flourishing in Utah's Great Salt Lake valley within the last 40 years appears to be from such an introduction. As an example of the ease with which transplanted individuals can succeed, raccoons from Indiana (midwestern United States) have reportedly been able to flourish on islands off the coast of Alaska.
The raccoon's expansion in various areas may also be due to the spread of agriculture. Raccoons have been able to exploit crops, especially corn but also cereal grains, which have become dependable food sources for them. The expansion of agriculture, however, does not necessarily lead to rapid increases in their abundance. Farming in Kansas and eastern Colorado (central and western United States) proceeded rapidly in the 1870s and 1880s, but this was about 50 years before raccoons started to spread out from their major habitat, the wooded river bottomlands. They have also expanded into many areas lacking any agriculture other than grazing and into places without forests or permanent streams.
Prior to Europeans settling and farming the Great Plains Region, raccoons probably were just found along its rivers and streams and in the wooded areas of its southeastern section. With the possible exception of the southern part of the province of Manitoba, their absence was notable throughout Canada. They first became more widely distributed in the southern part of Manitoba, and by the 1940s were abundant throughout its southeastern portion. In the 1950s their population swelled in Canada. The control of coyotes in the prairie region in the 1950s may have been a factor in raccoon expansion. If their numbers are sufficient coyotes might be able to suppress raccoon populations (though little direct evidence supports this notion). By the 1960s the raccoon had become a major predator of the canvasback ducks nesting in southwestern Manitoba.
The extermination of the wolf from most of the contiguous United States may have been a critical factor in the raccoon's expansion and numerical increase. In the eighteenth century, when the wolfs range included almost all of North America, raccoons apparently were abundant only in the deciduous forests of the East, Gulf Coast, and Great Lakes regions, though they also extended into the wooded bottomlands of the Midwest's major rivers. In such areas, their arboreal habits and the presence of hollow den trees should have offered some protection from wolves and other large predators. Even though raccoons may not have been a significant part of their diet, wolves surely would have tried to prey on those exposed in relatively treeless areas.
更多托福阅读考试信息
了解环球教育托福课程
相关阅读
-
预约托福水平在线测试
获取0元体验课程