GWD-2-2

ponny

GWD-2-2:The primary purpose of the passage is to

A.      point out some of the differences between dominant and keystone species

B.      emphasize the complexity of the interactions that occur between two particular species

C.      detail the effect of a particular habitat on the role occupied by a certain keystone species

D.     illustrate the importance of community diversity for the perpetuation of an ecosystem

E.      explain some considerations involved in determining whether a species occupies a keystone role

E

请问C答案是什么意思阿？读起来总觉得怪怪的．谢谢！

beautywawa

樓主有沒有文章呀,,貼出來看看吧..

wangyu73cn

While the most abundant and dominant species within a particular ecosystem                  1

is often crucial in perpetuating the ecosystem, a “keystone” species, here defined                    2

as one whose effects are much larger than would be predicted from its appearance,               3

also play a vital role.  But because complex species interactions may be involved,                 4

identifying a keystone species by removing the species and observing changes   in                   5

the ecosystem is problematic.                                                                                                6

       It might seem that certain traits would clearly define a species as a keystone                    7

species; for example, Pisaster ochraceus is often a keystone predator because it                         8

consumes and suppresses mussel populations, which in the absence of this starfish                  9

can be a dominant species.  But such predation on a dominant or potentially dominant          10

species occurs in systems that do as well as in systems that do not have species that               11

play keystone roles.  Moreover, whereas P. ochraceus occupies an unambiguous                 12

keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats                13

the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand                    14

burial is responsible for eliminating mussels.  Keystone status appears to depend on                    15

context, whether of particular geography or of such factors as community diversity                 16

(for example, a reduction in species diversity may thrust more of the remaining species           17

into keystone roles) and length of species interaction (since newly arrived species                   18

in particular may dramatically affect ecosystem).

The primary purpose of the passage is to

A.      point out some of the differences between dominant and keystone species

B.      emphasize the complexity of the interactions that occur between two particular species

C.      detail the effect of a particular habitat on the role occupied by a certain keystone species

D.     illustrate the importance of community diversity for the perpetuation of an ecosystem

E.      explain some considerations involved in determining whether a species occupies a keystone role

本题答案应该为E吧。全文应该是贯穿这一主题的。
C选项是说，“对于特定栖息地点之于'keystone'物种功能的影响，进行详细地阐述。”此选项应该不是文中的主线，仅仅是一种细节论述。

[此贴子已经被作者于2005-3-4 23:59:13编辑过]

ponny

谢谢wangyu73cn！

梦不落

想问下为什么我的gwd-2里面没有这篇文章呢？我用的是taotao 31，携影也没有啊。。。这是哪个版本的呢？

谢谢！

BOASU

我下载的那份资料答案给的是D，，看来是答案错了，，

我最开始也选E看到第二段第一句很容易觉得本文是要讨论如何辨别keystone.

但是再读下去就会发现，第二段整段都是在讨论不同的环境对keystone species角色的影响。并没有提到在各种环境下如何鉴别。所以C项是最合理的。

看来做gwd抓主题句还远远不够啊！