Predators are those organisms using other organisms as a source of protein. Without predators a species' survival may be compromised, eg. it may become genetically weak through a dampening of instinctive responses.
Among the top of the food-chain predators in south-west wetlands of Western Australia is the tiger snake (Notechis scutatus). The individual frogs, birds, turtles and lizards taken, apart from those with physical flaws, are generally those with a reduced instinctive response to threat. Be it in their selection of shelter sites, foraging behaviour, activity periods, etc. The tiger snake, by removing these genetically flawed individuals, contributes to the natural selection process. That is, it fine tunes the genetic fingerprint for success in the other organisms at that particular point in time and in that particular environment.
The result is a strengthening of the prey species along with a corresponding strengthening of the predator species to remain viable by continuing to successfully hunt.