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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 waterfowl-nest 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.
Q 15:
The primary purpose of the passage is to
A.describe some procedures used for wildlife management and consider some problems associated with the execution of those procedures
B.outline a problem related to a wildlife management procedure and offer potential explanations for the results of an experiment bearing on that problem
C.present experimental results that illustrate the need for certain wildlife management procedures and point out some inconsistencies in those results
D.argue that a certain procedure used for wildlife management should be modified because of its unintended consequences
E.propose that further experiments be performed to assess the long-term effects of certain wildlife management procedures
答案B
我选A
主旨题总做不对……A consider some problems associated with the execution of those procedures怎么错了，problem就是讲的remove predator的方法行不通么 |
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发表于 2011-7-21 04:50:49
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