Predator – Prey relationship: - It acts as a powerful extrinsic regularly mechanism. The interplay between the predator – prey results in a co evolutionary game between the two. In the process both the species evolve and regulate each others populations. Predation has the regulatory effect especially in ungulates where the predator is a highly skilled carnivore. Deer, moose and caribou are not known to have intrinsic population controls. Similarly, plant predators like deer and rabbits have a regulatory effect on plant population.