Predation alone doesn't explain elk population reductions

Wolves reduce elk numbers by killing them, but it’s likely that they also decrease elk reproduction, according to a Montana State University study. In a seminar at MSU on Thursday, ecology professor Scott Creel presented more evidence indicating that reintroducing wolves into the ecosystem has affected elk populations in some unforeseen ways. Creel and co-author David Christianson also presented the study to the Society of Conservation Biology last week. Creel’s research was based upon 12 elk management units in Montana, Wyoming and Yellowstone National Park that all had 30 years of data on elk populations, predators and climate characteristics. Several factors act together to affect elk population swings, including the severity of the winter, elk population density, human hunters and animal predators — including wolves, lions and grizzly bears. For areas without wolves, scientists can predict what elk populations will do if there is a severe winter or if the herd density gets too high. In both cases, populations will drop because fewer calves are born or survive. But for areas with wolves, winter severity and elk density no longer produce the same population responses. Calf survival still declines in a bad winter, but it doesn’t increase as much again in a mild winter. The likely explanation, he said, is that elk are more vigilant and feed less around predators. Diet and activity changes can cause females to have less energy to produce calves, a response that has been shown to occur in several animal species. “I think the cost of anti-predator behavior explains a significant proportion of those missing calves,” Creel said. “When we did the EIS, we didn’t deal with the possibility that elk will start doing things differently to avoid predation, but those things that they do may carry physiological consequences.”...more