Gray wolves once roamed the western portions of North America from Alaska to Mexico. Gray wolves prey on bison, deer, elk, and moose. These prey had been depleted by hunting by settlers. Ranches and farms were built near gray wolf habitat. The wolves thus began to prey on livestock. When the federal government set aside the Greater Yellowstone Ecosystem (GYE) as a national park in 1872, about 300-400 wolves were present, preying mostly on elk and bison (Yellowstone Association 1996). Fearing the wolves' impact on elk and bison herds as well as livestock owned by area ranchers, the federal government began eradicating the wolf population. Bounty programs that continued until 1965 offered as much as $50 per wolf. By the 1930s, wolves had been effectively eliminated from the 48 contiguous states and Mexico and remained in high numbers only in Alaska. The elk population then grew. Elk grazed on plants and soon plant populations declined. Plants such as willow trees and aspen were negatively affected. Song birds depended on the trees for habitat, river banks remain stable because of the trees, but now the trees were not producing saplings (young trees). Which of the following is the best conclusion to make based on this situation?