Based on many climate-related ocean measurements, researchers are able to determine positive, average and negative NPO values. A positive NPO translates into a milder climate in most of western North America, but it means more severe weather in the mountain regions, where climate is more complex.
Hebblewhite analyzed the elk population in Banff National Park from 1985 to 2000 and cross-referenced his results with NPO values during that period. He found that positive NPO values translate into elk population declines in the park.
Severe weather in the mountains means colder and snowier conditions than usual. More snow is bad news for elk, which have heavy bodies and long, narrow legs and small hooves. The deeper the snow, the further they sink. Conversely, wolves have relatively light, sleek bodies and big, wide paws that act like snowshoes. In the Canadian Rockies, wolves rely on elk meat for 40 to 70 per cent of their diet.
"The elk are already at a deficit in the winter. There is less grass to eat, and their bodies have to work harder and use more energy to stay warm," said Hebblewhite, who studies in the U of A Department of Biological Sciences.
Cold, wet weather alone is enough to decrease an elk population, but when wolves are added to the environment, elk become especially vulnerable. Hebblewhite found that the combination of positive NPO values and wolf predation were related to 50 per cent declines in the elk population.
Hebblewhite noted that positive NPO values and severe weather in the Canadian Rockies are occurring more frequently, and the trend is likely related to global warming. However, he added that the elk
Source:University of Alberta