Bison breed from mi… Elk are some of the most important and influential animals in the Greater Yellowstone Ecosystem.Elk have shaped the environment of the park, affecting plant growth, influencing the materials beavers use to build dams, and even impacting stream temperatures. About 21,000 remain in the park through the winter.Â. Fish and Aquatic Species in Yellowstone National Park. Their decreased populations have historically led to increased elk populations (since they are prey of the wolves), and thus decreased aspen tree populations (as elk eat/damage these plants). The National Elk Refuge in Jackson Hole, Wyoming, is a winter sanctuary for several thousand elk from the Bridger-Teton National Forest as well as Yellowstone and Grand Teton national parks. //-->,