Final answer:
Wolves in Yellowstone National Park travel in packs to bring down primarily elk, and their presence as a keystone species has led to significant ecological changes, including improved habitats for various species.
Step-by-step explanation:
In Yellowstone National Park, wolves, which are a keystone species, travel in packs to bring down their prey, which primarily includes elk. The reintroduction of wolves to the park in 1995 resulted in elk changing their grazing behavior to avoid predation, particularly in exposed stream and riverbeds like the Lamar Riverbed. As a consequence, willow and cottonwood seedlings were able to grow, which decreased erosion and improved the habitat for other species like fish and beavers, thereby showing the profound impact of predator presence on ecosystem dynamics.