YELLOWSTONE NATIONAL PARK, Wyo. — The vast, sagebrush-studded valleys in this huge chunk of wild country, teeming with herds of elk and bison, are home these days to 10 packs of wolves.Once among the first species to be listed as endangered, the gray wolf has made a healthy comeback within Yellowstone National Park and its bordering states. Since 1995-96 when 31 wolves were trucked into the park from Canada, their numbers have grown and stabilized to the point that officials could essentially post a “no vacancy sign” at Yellowstone. That’s because the park’s wolf population has hovered for the last decade at 100, give or take, which experts consider Yellowstone’s carrying capacity.Protected on parkland, gray wolves show little fear of humans, often living out their lives within view of roads. They attract thousands of tourists a year who sometimes become witnesses to the life-or-death dramas between predator and prey.And some catch a glimpse of a rare white wolf.