Apex predators directly impact those they prey upon and cause a ripple effect on their environment. The red-tailed hawk can shift from one prey species to another. If one species is abundant it might be easier to catch and more of the abundant species will be caught. Should a new species become abundant it will be preyed upon.
By eating what it can find an apex predator in a prey rich environment prevents any single species from becoming dominant. The relationships between predator and prey seem complicated but are simple compared to the complexity of the apex predator’s impact on its environment. Each prey choice has its own environmental impact.