gwd 2 question 2

moon05

Question 2 – 4:

      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).                                                    19

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Question 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

这题为何选 D. 我选的是E, 为什么不对呢?

beautywawa

參考看看唷!

GWD讨论总结－by fair_sword
http://forum.chasedream.com/dispbbs.asp?boardID=25&ID=56774&page=1

moon05

那里面只有QUESTION 5-8, 没有 QUESTION 2.  还请帮忙指点一下. 多谢多谢!

xealot

I also think D looks a bit better...

moonmood

这道题为什么选d呢？

我选的e, 麻烦选d的朋友解释一下

juningw

这个section，我选择的是：2～4分别是：E，B，D。

供参考

Alice01

我选择的也是：2～4分别是：E，B，D。