What is the main ecological trade-off associated with heavy lateral plates in sticklebacks?

• A. Better camouflage and no costs
• B. Increased protection against predators but higher energy cost and slower growth; in predator-poor habitats, selection favors reduced armor
• C. No effect on fitness
• D. Increases mating success in all habitats

Answer: (B)

The key idea is that a trait can be helpful in one situation but costly in another. Heavy lateral plates act as armor, boosting survival when predators are common. But building and maintaining that armor uses energy and resources that could otherwise go to growth, reproduction, or better foraging. In habitats with lots of predators, the survival benefit of armor outweighs the costs, so heavy plates persist. In predator-poor environments, the protection isn’t as valuable while the energetic costs remain, so natural selection favors reduced armor to save energy and allow faster growth. This explains why sticklebacks show more heavy plating in high-predation areas and reduced or few plates where predators are scarce.