Predators play a crucial role in controlling prey populations in ecosystems through predation. By preying on the prey species, predators help regulate their population sizes. This can prevent overgrazing or overpopulation of certain species, which can have cascading effects on the entire ecosystem's balance. Additionally, the fear of predation can also influence the behavior of prey animals, leading them to alter their patterns of movement, feeding, and reproduction to avoid being caught by predators.