What is the keystone species?

Options

A. A species which makes up only a small proportion of the total biomass of a community, yet has a huge impact on the communit's organization and survival.
B. A common species that has plenty of biomass, yet has a fairly low impact on the community's organizaiton
C. A rare species that has minimal impact on the biomass and on other species in the community.
D. A dominant species that costitutes a large proportion of the biomass and which affects many other species.

Answer

### Step-by-Step Solution:

1. **Definition of Keystone Species**:
- A keystone species is defined as a species that has a disproportionately large effect on its environment relative to its abundance. This means that even if the population of a keystone species is small, its impact on the ecosystem is significant.

2. **Importance of Keystone Species**:
- Keystone species play a crucial role in maintaining the structure of an ecological community. They help regulate populations of other species and contribute to the overall health and stability of the ecosystem.

3. **Consequences of Removing Keystone Species**:
- The absence of a keystone species can lead to significant changes in the ecosystem, potentially resulting in its collapse. This is because other species that depend on the keystone species for survival may decline or disappear.

4. **Examples of Keystone Species**:
- Examples include predators, such as wolves, which control the population of herbivores, or certain plants that provide essential resources for other organisms in the ecosystem.

5. **Identifying Keystone Species**:
- When identifying a keystone species, one should look for species that, despite having a small biomass or population size, have a large impact on the community and ecosystem dynamics.

6. **Correct Option**:
- Based on the definitions and explanations, the correct option for defining a keystone species is: "species which makes up only a small proportion of the total biomass of a community yet has a huge impact on communities, organizations, and survival."