Grassland songbirds often nest in the same grassland-wetland complexes as waterfowl, particularly in a certain part of those complexes, namely, upland habitats surrounding wetlands. Although some wildlife management procedures directed at waterfowl, such as habitat enhancement or restoration, may also benefit songbirds , the impact of others, especially the control of waterfowl predators, remains difficult to predict. For example, most predators of waterfowl nests prey opportunistically on songbird nests, and removing these predators could directly increase songbird nesting success. Alternatively, small mammals such as mice and ground squirrels are important in the diet of many waterfowl-nest predators and can themselves be important predators of songbird nets. Thus. Removing waterfowl-nest predators could affect songbird nesting success through subsequent increases in small-mammal populations.
In 1995 and 1996, researchers trapped and removed certain waterfowlnest predators. primary raccoons and striped skunks, then observed subsequent survival rates for songbird nests. Surprisingly. They observed no significant effect on songbird nesting success. This may be due to several factors. Neither raccoons nor striped skunks consume ground squirrels, which are important predators of songbird nests. Thus, their removal may not have led to significant increases in populations of smaller predators. Additionally, both raccoons and striped skunks prefer wetlands and spend little time in upland habitats; removing these species may not have increased the nesting success of songbirds in the uplands enough to allow detection.
It can be inferred that the habitat preferences of raccoons and striped skunks affected the results of the experiment described in the passage for which of the following reasons?
Songbird nests in the wetlands are usually located in places that most waterfowl-nest predators cannot reach.
Raccoons and striped skunks are not usually found in areas where songbird nests tend to be located.
Mice and ground squirrels tend to avoid predation by raccoons and striped skunks by remaining exclusively in the uplands.
The populations of small mammals in the wetlands are usually controlled by larger waterfowl-nest predators such as raccoons and striped skunks.
The waterfowl on which raccoons and striped skunks prey in the wetlands compete with songbirds for food.
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正确答案是 B。因为文章指出,1995年和1996年研究人员捕捉和清除了特定的水禽巢穴捕食者,主要是浣熊和条纹臭鼬,然后观察歌鸟巢穴的随后生存率。令人惊讶的是,他们没有观察到歌鸟巢穴的成功率有显著影响。这可能是由于几个因素:浣熊和条纹臭鼬不吃地鼠,这些动物是歌鸟巢穴重要的捕食者,因此它们的消失可能不会导致小捕食者数量的显著增加。此外,浣熊和条纹臭鼬都偏好湿地,在上山生境很少待,清除这些物种可能不足以增加歌鸟在上山地区的巢穴成功,以至于无法检测到。由此可以推断,浣熊和条纹臭鼬的栖息地偏好影响了该实验的结果,因为它们通常不在歌鸟巢穴所在的地方。因此,B选项是正确答案。
A选项错误原因:文章第二段只讲了Raccoons and striped skunks很少在upland habitats,也就是songbird nests所在的地方,但是不能以此推断出所有的most waterfowl-nest predators就不能到,不能用特殊推出一般
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