New York Times: The grassy sweep of the Lamar Valley in the northeastern corner of this park is famous for its wildlife, especially its vast herds of elk and bison and the wolves that hunt them. But while walking across the Lamar last fall, Robert L. Crabtree, chief scientist with the Yellowstone Ecological Research Center in Bozeman, Mont., pointed out a cascade of ecological changes under way. The number of grizzly bears and gophers in the valley has increased, Dr. Crabtree said, an increase …