Q. Consider the following mechanisms employed by animals:

1. Hibernation
2. Migration
3. Diapause
4. Aestivation

Which of the above are adopted by animals to overcome stressful external environmental conditions?
Answer: All of the above
Notes: All four options—hibernation, migration, diapause, and aestivation—are adaptive mechanisms animals use to overcome external environmental stress. Hibernation and aestivation allow escape in time, diapause is a suspended developmental stage, and migration offers escape in space. Each strategy allows survival during adverse conditions such as extreme temperatures or resource scarcity.