[求助]GWD-25-Q13

Jeffrey-N

GWD-25-Q13-Q15Grassland songbirds often nest in



the same grassland-wetland complexes



as waterfowl, particularly in a certain



Line part of those complexes, namely,




(5) upland habitats surrounding wetlands.



Although some wildlife management



procedures directed at waterfowl, such



as habitat enhancement or restoration,



may also benefit songbirds , the impact



(10) of others, especially the control of



waterfowl predators, remains difficult to



predict. For example, most predators



of waterfowl nests prey opportunistic-



ally on songbird nests, and removing



(15) these predators could directly increase



songbird nesting success. Alterna-



tively, small mammals such as mice



and ground squirrels are important



in the diet of many waterfowl-nest



(20) predators and can themselves be



important predators of songbird



nets. Thus. Removing waterfowl-nest



predators could affect songbird nesting



success through subsequent increases



(25) in small-mammal populations.



In 1995 and 1996, researchers



trapped and removed certain waterfowl-



nest predators. primary raccoons and



striped skunks, then observed subse-



(30) quent survival rates for songbird nests.



Surprisingly. They observed no sig-



nificant effect on songbird nesting



success. This may be due to several



factors. Neither raccoons nor striped



(35) skunks consume ground squirrels,



which are important predators of song-



bird nests. Thus, their removal may



not have led to significant increases



in populations of smaller predators.



(40) 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 13:



According to the passage, which of the
following is true about the role played
by ground squirrels in the ecology of
   grassland-wetland complexes?

A.
While not important in the diet of
raccoons or striped skunks, ground
squirrels are a significant source
of food for other waterfowl-nest
predators.

B.     Whereas ground squirrels are
   typically important as predators of
   songbird nests, their opportunistic
   predation on waterfowl nests also
   has an observable effect on waterfowl nesting success.



C.
Although most waterfowl-nest
predators prey on small mammals
such as mice and ground squirrels,
populations of ground squirrels tend
to increase quickly enough to compensate for this level of predation.



D.
Although ground squirrels have been
known to prey on songbird nests, a
larger portion of their diets is usually
provided by predation on waterfowl
nests.



E.
Since larger predators tend to prefer
small mammals to songbird eggs as
a food source, a large population of ground squirrels plays an important
role in controlling opportunistic
predation on songbird nests.




答案是A，请问B为什么不对呢？我觉得就题目中说土拨鼠在鸟的生态均衡系统中起的作用而用，应该是B更加切题才对啊。A说的是土拨鼠作为人家的食物，***不吃它，但是其他的要吃它，和在鸟的生态均衡系统中起的作用没关系啊。

xiaohaotoutou

ground squirrels are important for waterfowl-nest predators, but when researchers removed some reccoons and skunks, the effect on songbird nesting is not very significant.  therefore,  ground squirrels are not important in the diet of raccoons and striped skunks, but do for other predators.
the answer is A

Jeffrey-N

那么B到底为什么错呢？

如果要把实验结合起来的话，A对B错，因为实验中土拨鼠没起到什么作用。是不是应该这样理解这道题目啊？

luciferc

waterfowl predator 吃 squirrels 吃 songbird

waterfowl predator 也可直接吃songbird

对我来说 B关系 文章没有提过 我也推不出来

Jeffrey-N

刚才又看了一遍文章，知道B为什么错了。

Whereas ground squirrels are
  typically important as predators of
  songbird nests, their opportunistic
  predation on waterfowl nests also
  has an observable effect on waterfowl nesting success.
后半句不对，文中没有提到土拨鼠吃水鸟，只是说土拨鼠吃songbird 。我太粗心啦。

欧罗巴

刚才又看了一遍文章，知道B为什么错了。

Whereas ground squirrels are
  typically important as pred ...
Jeffrey-N 发表于 2013-1-15 21:10

    多读两遍