[求助]GWD25-Q 13

yangliu0401

Grassland 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.

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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 water-

fowl 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 com-

pensate 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，可偶从文中推不出相关的内容，偶就选E了，还请NNs指点啊

[此贴子已经被作者于2009-1-8 22:18:57编辑过]

UMLwang

Alterna-

tively, small mammals such as mice

and ground squirrels are important

in the diet of many waterfowl-nest
                    

(20) predators

That explained second part of Choice A.

yangliu0401

以下是引用UMLwang在2009-1-9 4:15:00的发言：
Alterna-

tively, small mammals such as mice

and ground squirrels are important

in the diet of many waterfowl-nest
     

(20) predators

That explained second part of Choice A.

谢谢~原来自己理解错了