❓ Câu hỏi According to the passage, why is the identification of keystone species often challenging?
- A. A. Keystone species are always rare and difficult to observe in the wild.
- B. B. Their ecological effects can vary depending on environmental conditions and time.
- C. C. The concept only applies to predators, making it hard to test with herbivores.
- D. D. Removing a keystone species usually has no noticeable impact on the ecosystem.