Official 38 Passage 2


The Racoon's Success


According to paragraph 6, during the eighteenth century, raccoons were abundant only in forests and wooded bottomlands of major rivers mainly because those were the only places where raccoons

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  • A
    were relatively safe from conflict with humans
  • B
    had little trouble finding sufficient food
  • C
    had some protection from wolves
  • D
    could find a varied diet of prey
正确答案: C

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  • 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 regionA vast grassland region in North America extending from central Canada south through the west central United States into Texas, 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 wolf's 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.

  • 浣熊有着横贯大陆的广泛分布,北美洲和中美洲的大部分都有他们的身影。 从加拿大的南部一直到巴拿马,以及在沿海地区的岛屿上都可以找到浣熊的足迹。 美国本土的49个州都有它们的分布。 尽管浣熊本来只存在于西半球,它们也成功迁移到了其他地方。

    在二十世纪三十年代,浣熊的数量跌倒了一个相对低点,1943年它们的繁殖季之后,浣熊的数量又开始发展壮大。 浣熊数量的快速增长贯穿了上世纪40年代始终,之后便一直维持着高位。 到上世纪80年代末,北美洲的浣熊数量至少是30年代数量的15到20倍。 到如今,浣熊的数量无疑又增长了很多,因为它们不断的扩展到新的栖息地,这些栖息地之前没有或者很少有浣熊的存在,比如,沙地草原、沙漠、沿海湿地以及山地。 它们在落基山西部的分布就是它们快速开拓新环境的典型示例。 尽管浣熊的数量收获了大幅增长,有时候会因为疾病有偶然性的下滑,浣熊的数量一直保持着较高水平。

    一些因素能够解释浣熊在数量和分布范围上的快速增长。 首先,它们的成功一部分归因于城市的发展,因为它们经常活跃在郊区甚至是城区。 此外,它们还被有意引入美洲大陆的各个地方。 在美国内部,浣熊经常被从一个地方带到另一个地方,有些是合法的有些是非法的,它们被用来重建狩猎区,或者因为人们仅仅是希望浣熊成为当地动物种类的一部分。 过去的40年间它们在犹他州大盐湖谷底的出现和繁荣发展就是源于这种引入方式。 美国中西部的印第安纳州的浣熊能够在阿拉斯加海岸附近的小岛上繁荣兴旺,这正是迁移引入的一个很好的例子。

    浣熊在不同地区的扩展分布也许也是因为农业的发展。 浣熊能够采摘农作物,尤其是玉米,也包括谷类,是浣熊的主要食物来源。 农业的扩张并不一定会引起浣熊数量的急剧增长。 十九世纪70年代至80年代,农业在堪萨斯州和科罗拉多州东部地区快速发展,但是直到50年后浣熊才从主要栖息地—长满树木的河流低地—开始向外扩张。 它们甚至也向只有牧场没有其他农业的地区扩张,或者进入没有树林或常年河流的地方。

    在欧洲人于大平原地区安家和耕作之前,浣熊在该地区的河流、溪流沿岸以及该地区的东南部树林里就已经存在了。除了马尼托巴省南部地区之外,整个加拿大都难以找到浣熊。刚开始它们只是在马尼托巴省南部分布更为广泛一些,直到二十世纪40年代,浣熊数量在该省东南部就已经相当可观了。 在二十世纪50年代,浣熊数量在加拿大快速上升。 二十世纪50年代平原地区丛林狼的控制也许是浣熊向外扩张的原因之一。 如果他们数量够多的话,丛林狼是可以控制浣熊数量的(尽管几乎很少有直接证据支持这一观点)。 到二十世纪60年代,浣熊成了马尼托巴省西南部的灰背野鸭的主要捕食者。

    在相邻的美国,狼的灭绝或许是浣熊数量快速增长的关键因素。 在18世纪,当时狼分布于北美的绝大部分,而浣熊只在东部的落叶林中、墨西哥湾沿岸地区、五大湖区大量分布,虽然它们也向中西部主要河流沿线的树木繁茂的低地扩张。在这些地区,浣熊择木而居的习惯和中空树洞的存在,一定程度上保护了它们不被狼和其他大型捕食动物猎食。虽然浣熊不是它们的主要食物来源,在相对缺少树木保护的地方,狼还是会去捕食暴露在外的浣熊的。
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    题干分析:可用题干关键词“forests and wooded bottomlands”定位到第六段第二句,答案在后面的第六段第三句。

    原文定位:第六段第三句In such areas, their arboreal habits and the presence of hollow den trees should have offered some protection from wolves and other large predators.