Yellowstone National Park: On a recent northern autumn afternoon in the Lamar Valley, visitors watched a wolf pack lope along a thinly forested riverbank, 10 or so black and grey figures shadowy against the snow. A little further along the road, a herd of bison swung their great heads as they rooted for food in the sagebrush steppe, their deep rumbles clear in the quiet, cold air.

In the United States, Yellowstone National Park is the only place bison and wolves can be seen in great numbers. Because of the park, these animals survive. Yellowstone was crucial to bringing back bison; reintroducing grey wolves; and restoring trumpeter swans, elk and grizzly bears - all five species driven toward extinction found refuge here.

But the Yellowstone of charismatic megafauna and of stunning geysers that 4 million visitors a year travel to see is changing before the eyes of those who know it best. Researchers who have spent years studying, managing and exploring its roughly 8800 square kilometres say that soon the landscape may look dramatically different.

During the next few decades of climate change, the country's first national park will quite likely see increased fires; less forest; expanding grasslands; shallower, warmer waterways; and more invasive plants - all of which may alter how, and how many, animals move through the landscape. Ecosystems are always in flux, but climate change is transforming habitats so quickly that many plants and animals might not be able to adapt well or at all.