Key stone species is

Options

A. always dominant
B. useful in maintaining structure and function of biotic community
C. with maximum biomass
D. all of the above

Answer

### Step-by-Step Text 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 a keystone species is not the most numerous, its presence or absence significantly impacts the ecosystem.

2. **Role in Ecosystem**: Keystone species play a critical role in maintaining the structure, diversity, and function of an ecosystem. They help regulate populations of other species and contribute to the overall health of the ecosystem.

3. **Impact on Biodiversity**: The presence of keystone species can influence the types and numbers of other species in the community. For example, they may control the population of herbivores, which in turn affects plant communities, or they may provide essential resources for other species.

4. **Not Necessarily Dominant**: It is important to note that keystone species are not always the most dominant or abundant species in an ecosystem. Their impact is more about their role and function rather than their biomass.

5. **Examples of Keystone Species**: Common examples of keystone species include predators like wolves, which control the population of herbivores, or certain plants that provide critical habitat or food sources for other organisms.

6. **Conclusion**: In summary, a keystone species is essential for maintaining the structure and function of its ecosystem, and its influence can be significant despite its relatively low biomass.