What is a keystone species?

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding 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. **Characteristics of Keystone Species**: Keystone species play a critical role in maintaining the structure of an ecological community. They can influence the types and numbers of various other species in the ecosystem. Their presence or absence can lead to significant changes in the ecosystem.

3. **Examples of Keystone Species**:
- **Ants**: Ants are a classic example of a keystone species. They contribute to the decomposition process by breaking down organic matter and recycling nutrients back into the soil. If ants were removed from an ecosystem, there would be an accumulation of waste, leading to negative impacts on other species.
- **Beavers**: Beavers are another example. They create wetlands by damming rivers, which can lead to the formation of new ecosystems. Their activity can increase biodiversity by creating habitats for various other species.

4. **Identifying the Correct Option**: Given the options provided in the question, the correct definition of a keystone species is:
- **Option C**: A species which makes up only a small proportion of the total biomass of the community yet has a huge impact on the community's organization and survival.