Wolves transformed Yellowstone Park,, even changed the rivers. Watch 4 minute Trophic Cascade talk by George Monbiot

 As a warm up, try a few paragraphs from "Yellowstone: How Not To Manage A National Park".  Lying eco-elites in the Park Service were killing  predators and favouring others, making a wasteland of the park.  Reminds me of today's Covid-elites casting their policy curses on the people while believing in their own purity of heart.  

Overgrazing changed the flora. Aspen and willows were being eaten (by elk) at a furious rate and did not regenerate. Large animals and small began to disappear from the park.

In an effort to stem the loss, the park rangers began to kill predators, which they did without public knowledge. They eliminated the wolf and the cougar, and they were well on their way to getting rid of the coyote. Then a national scandal broke out. New studies showed that it wasn’t predators that were killing the other animals. It was overgrazing from too many elk. The management policy of killing predators therefore had only made things worse.  

Actually, the elk had so decimated the aspen that now, where formerly they were plentiful, now they’re quite rare. Without the aspen, the beaver, which use these trees to make dams, began to disappear from the park. Beaver were essential to the water management of Yellowstone, and without dams, the meadows dried hard in summer and still more animals vanished.

And now the video:  The "Trophic Cascade" from a small population of wolves is a real thing and so is the change in how the rivers flow and how the banks flourish.