GWD2-v3

Qiongwang01

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 3:

Which of the following, if true, would most clearly support the argument about keystone

status advanced in the last sentence of the passage (lines 15 – 19)?

A.      A species of bat is primarily responsible for keeping insect populations within an

ecosystem low, and the size of the insect population in turn affects bird species

within that ecosystem.

B.      A species of iguana occupies a keystone role on certain tropical islands, but does

not play that role on adjacent tropical islands that are inhabited by a greater number

of animal species.

C.      Close observation of a savannah ecosystem reveals that more species occupy

keystone roles within that ecosystem than biologists had previously believed.

D.     As a keystone species of bee becomes more abundant, it has a larger effect on

the ecosystem it habits.

E.      A species of mouse that occupies a keystone role in a prairie habitat develops

coloration patterns that camouflage it from potential predators.

The answer is B,  why it is not D

LES

偶的理解，仅供参考。

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

这段话只讲了什么时候出现keystone role，但没有说它的具体影响的大小。

LES

这套题目的答案有些混乱，欢迎大家积极讨论。谢谢先！

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

Answer:

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Question 4:

The passage suggests which of the following about the identification of a species as

a keystone species?

A.      Such an identification depends primarily on the species’ relationship to the dominant species.

B.      Such an identification can best be made by removing the species from a particular

ecosystem and observing changes that occur in the ecosystem.

C.      Such an identification is likely to be less reliable as an ecosystem becomes less diverse.

D.     Such an identification seems to depend on various factors within the ecosystem.

E.      Such an identification can best be made by observing predation behavior.

Answer:

future2005

Q2: E

Q4: D

手头没有答案, 请大家讨论.

valarie

以下是引用future2005在2004-9-8 23:04:00的发言：

Q2: E

Q4: D

手头没有答案, 请大家讨论.

Agree. and Q3: B.

dashasha

太好了，有NN跟我选的一样。帮我confirm了。

swlfx

同意future2005

weichenli

agree..totally ! thank you guys cause i was scared to hell when i checked with the ans provided ( appears to be wrong)

Dinaxie

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            

play keystone roles.

帮我翻译一下嘛！

wangyu73cn

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            

play keystone roles.

估计，第一部分的画线部分省略了 have species that play keystone roles