When the moth, which feeds on this cactus, was introduced, it rapidly brought the cactus under control. Some years later both moth and cactus were rare, and it is unlikely that the casual observer would ever think that the moth had accomplished this. Once the cactus became sufficiently rare, the moths were also rare, and unable to find and eliminate every last plant. Inadequate dispersal is perhaps the only factor that keeps the cactus moth from completely exterminating its principal food source, the prickly pear cactus. Prey defenses can be a stabilizing factor in predator-prey interactions.
Predation can be a strong agent of natural selection.
Examples include camouflage in the peppered moth, and prey that are nocturnal to escape detection. Often a predator eats more than one prey. If a predator switches between prey A and B on the basis of their frequency, it will eat A when B is rare and B when A is rare. The prey should exhibit mild oscillations, and the predator should fluctuate little. This would stabilize prey abundances.