The return of wolves to Yellowstone National Park is one of the greatest trophic rewilding stories. A new paper synthesises over 40 years of research to tell the scientific story.
Professor Mark Boyce’s key conclusion is that there was not one, but many trophic cascades, and that these trophic cascades happened in different places and at different times (spatial and temporal variability). During the summer for example, elk avoid wolves by climbing to higher, steeper habitat. Hunting also tends to takes place at dusk and dawn, to the extent that “elk appeared to ignore wolves during the day”. Such differences in space and time increase heterogeneity (things are distributed more patchily than uniformly).
These trophic cascades are further complicated by rebounding populations of grizzly bears, cougars and bison. Bears steal wolf kills, and are also specialised at taking elk calves. Cougars are subordinate predators to wolves, and their behaviour changes as the wolf population expands.
Boyce also believes that “the consensus will be that numerical declines in elk have contributed more to trophic cascade than has behavioural avoidance of wolves”, slightly challenging the Landscape of Fear theory. In other words, Yellowstone rewilding is more about wolves killing deer than scaring them.
Rewilding in Yellowstone would not have happened without the National Park Service’s policy of “ecological process management”, which actually minimises management and lets fires, floods, carnivores and herbivores lead the way. However, according to Boyce this policy under threat by political pressure to control the growing bison population.
Boyce is sceptical of concerns that “heavy grazing and browsing” by bison might “damage” vegetation:
“We do not know how bison will affect Yellowstone, but surely we will learn a great deal more if we allow the bison population to take its course rather than intervening in the fashion that will be arbitrary to the underlying ecological system. Whatever influence we can have as scientists, we must insist that the National Park Service maintain its policy of ecological process management for their Crown Jewell that is Yellowstone National Park.”
Wolves for Yellowstone: dynamics in time and space by Mark S Boyce was published in the Journal of Mammalogy on 10 October 2018 (Volume 99, Issue 5, Pages 1021–1031).