A. I only
B. II only
C. I and II only
D. I, II and III
参考答案:
C
本题详细解析:
The keystone species, by definition, is a species within a community with a disproportionate role to its abundance or biomass. It has a unique role in maintaining the balance and structure of the ecosystem. If the species were removed, it would have severe ramifications for the rest of the community.
[The analogy is the keystone in the architecture of an arch, if the stone is removed, the arch would collapse. Though small in size, this stone plays a key structural role in maintaining the arch.]
An example of a keystone species is the beaver, a small animal that builds a dam, flooding a river valley, allowing for fish, other aquatic animals and vegetation to flourish in the resultant water body that is formed. If the beaver were removed, the entire ecosystem would collapse.
A keystone species is not a dominant species, one that has a significant influence on the community because of its abundance or high biomass, it can be relatively rare compared to the other species in the ecosystem. Therefore, Choice D is incorrect. Choices A and B do not include both the correct statements.
