Elk populations have declined, but Reg Rothwell, supervisor of biological services for the Wyoming Game and Fish Department, said that the growing populations of grizzly and black bears and mountain lions, as well as drought conditions in recent years, could be as much to blame as wolves.
In any case, that was expected. Wolves hunt elk, and do it quite well, Bangs said.
But the ripple effect extends far beyond the elk.
For one thing, elk had to change their way of eating and that has affected not only plant life, but erosion patterns. Before the reintroduction of the wolf, elk in Yellowstone munched peacefully on saplings along river banks, killing the young willow, cottonwood and aspen before they could mature.
With wolves on the prowl, elk realized they could not safely eat along the banks of the winding rivers where they could not see a long way.
As a result, trees are growing in those areas for the first time in 70 years, and that has provided habitat for songbirds and encouraged a resurgence in the beaver population in the park.
Wolves, by regularly killing elk and deer and leaving the remains when they have eaten their fill, provide food for a host of animals such as lynx, bald eagles, golden eagles and others from grizzly bears to dung beetles that feast on carcasses.
"If you're a scavenger, wolves are the best thing since sliced bread," Bangs said.
On the other hand, as the wolves have thrived, coyote numbers have dropped. That has allowed the fox to flourish, which has not been good for ground nesting birds, a prime source of food for foxes.
But with fewer coyotes, there is less pressure on pronghorn antelopes, and their numbers have risen.
"Wolves serve a function in those biological communities where they live," said Nina Fascione, vice president for species at Defenders of Wildlife, an environmental group that was instrumental in bringing wolves back to the northern Rockies. "They are a keystone predator who have an effect beyond the immediate animals they prey on."
The argument over wolves has focused on their effect on big game animals such as deer and elk, and on livestock, and dispute over the extent of that effect and what to do about it is what has divided hunters and ranchers from the biologists, especially in Wyoming.
Bangs and Mike Jimenez, the FWS head wolf biologist for Wyoming, both said they believe the job of managing wolves should be the states', because they have more staff to deal with the situation and likely have a close relationship with ranchers and others affected by the wolves.
Ranchers' losses to predators have increased since wolves were brought back. For instance, Sommers said his annual calf losses to predators rose from less than 1.6 percent in 1990-94 to 3.6 percent annually in 1995-99 as the grizzly bear population grew and the reintroduced wolf gained a foothold, and then to 5.2 percent annually 2000-02 as wolf numbers grew rapidly.
The FWS also tracks losses and releases both annual and monthly reports on the interaction between wolves and humans. According to FWS figures, a total of three cattle and no sheep were killed by wolves in the northern Rockies in 1995. In 2003, according to FWS figures, 64 cattle and 211 sheep were killed.