A keystone species is a species that has a

Correct option is A

The correct answer is (a) Large effect on the community. A keystone species is one that has a disproportionately large effect on its ecosystem relative to its abundance. Its presence and role are crucial for maintaining the structure, diversity, and functioning of the ecosystem.
Explanation:
· Keystone species play a critical role in maintaining the balance of an ecosystem.
· If a keystone species is removed, it can lead to a dramatic shift in the ecosystem, potentially causing the collapse of the community structure.
· These species often affect multiple other organisms in the ecosystem and can influence predation, competition, and resource availability.
Examples of Keystone Species:
1. Sea Otters:
· Control sea urchin populations, which helps maintain kelp forest ecosystems.
2. Wolves:
· Regulate prey populations like deer, influencing vegetation growth and ecosystem balance.
3. Beavers:
· Create wetlands by building dams, which support diverse plant and animal life.
4. Starfish (Pisaster ochraceus):
· Control mussel populations, maintaining biodiversity in tidal ecosystems.
Additional Knowledge:
· (a) Large Effect on the Community:
· Correct. Keystone species have a significant impact on their environment, and their loss can disrupt the ecosystem.
· (b) Slow Effect on the Community:
· Incorrect. The effects of removing a keystone species are usually rapid and substantial.
· (c) Medium Effect on the Community:
· Incorrect. The impact of a keystone species is greater than would be expected based on its population size.
· (d) Average Effect on the Community:
· Incorrect. Keystone species have an effect that is far above average compared to other species.
Key Points:
1. Keystone species are essential for ecosystem stability.
2. Their removal can cause a trophic cascade, affecting the entire food web.
3. They can be predators, prey, ecosystem engineers, or mutualists.
4. Conservation efforts often focus on protecting keystone species to maintain biodiversity.
5. Examples include wolves, sea otters, beavers, and starfish.