Predator-prey relationship: This is an interaction between two species where one species, the predator, hunts and kills the other, the prey. In this case, wolves are predators to many animals in Yellowstone.
Trophic cascade: This is an ecological phenomenon triggered by adding or removing top predators from an ecosystem and seeing effects trickle down through every level of food web. The reintroduction of wolves caused a trophic cascade in Yellowstone.
Keystone Species:A species that has a disproportionately large effect on its environment relative to its abundance. Wolves are considered a keystone species in Yellowstone due to their significant impact on the ecosystem.