Carrion: It’s what’s for dinner Wolves As Keystones

Canis lupis “Who would not give a year of his life to see a wild wolf or a whole pack of wolves trailing down an elk or deer?” Edmund Heller 1925

Introduction Wolves viewed as competitors, threats to safety, symbols of evil Early 20th Century: gray wolves eradicated from 42% of range in North America Hunted to local extinction in Yellowstone National Park by 1926 Reintroduced in 1995 By 2006, the wolf population in the park was at least 136 wolves in 13 packs Today U.S. Fish and Wildlife reports 653 wolves in 130 verified packs

Timeline History of Gray Wolves in Yellowstone Park 1872 YNP is established by an act of the U.S. Congress 1872-1917 Wolves in and around YNP are killed for pelts, to protect humans and livestock, and for sport. 1918 The newly formed National Park Service takes control of YNP and continues to hunt wolves. 1926 Wolves are exterminated from YNP 1973 The U.S. govt. lists the gray wolf as an endangered species. 1995-1996 Thirty-one wolves are reintroduced into YNP 2011 653 wolves, in 130 verified packs, and 39 breeding pairs.

Population Figures for Montana

Wolves as Keystones Important to restore the gray wolf to Yellowstone because it is a keystone species. A keystone in an arch's crown secures the other stones in place. Keystone species play the same role in many ecological communities by maintaining the structure and integrity of the community.

Wolves as Keystones

Keystone Species Wolves have facilitated the recovery of beavers in Yellowstone. In the 1890s, human trappers decimated beaver populations

Keystone Species After wolves were removed, Elk populations grew Competition for willow increased Suppressed beaver population recovery

Keystone Species After wolves restored to YNP: Predation, hunting and drought have reduced elk populations.

Keystone Species Elk have thus changed behavior Move to coniferous forests for protection when they detect wolves No longer near streams to compete with beavers

Keystone Species Fewer elk in the willow habitat have resulted in increased beaver colonies on the northern range of YNP from one in 1996 to nine in 2003

Winter on the Northern Range In YNP, daytime winter temperatures range from -40oC to -5oC and snow can exceed 7 m at high elevations (NPS 2006) In the autumn, elk in northern YNP migrate from high elevation to a milder habitat

Winter on the Northern Range Winter isn’t easy for the elk Difficult to dig and move in deep snow In severe winters, elk regularly starve to death

Winter on the Northern Range Carcasses-particularly those of elk- are an important food source for Yellowstone carnivores Carnivores, like bears and eagles, scavenge carrion during winter and early spring. Ravens have learned to track wolves to kill sites

Winter on the Northern Range Carrion availability depended on winter severity w/out wolves Deep snow and low temperatures, elk carrion was plentiful Mild winters, carrion was sparse. During the rest of the year, carrion is negligible.

Winter on the Northern Range Even with wolves, snow plays a big role. Wolves leave more carrion for scavengers when snow is deep Elk are easier to kill and wolf packs eat a smaller proportion of each kill.

Winter on the Northern Range Presence of wolves = carrion available year- round Carrion is a more predictable resource for scavengers

Winter on the Northern Range Change in the timing and predictability of carrion benefits: Small scavengers (e.g. foxes), which have small stores of body fat and need to feed frequently Large scavengers (e.g. bears), which require a high energy food source before hibernation

Winter on the Northern Range No other carnivores in Yellowstone fill the ecological role of the gray wolf. Coyotes occasionally kill elk, but they feed primarily on small mammals and carrion Bears prey on elk only during some parts of the year. Cougars are a major year-round predator of elk, but they defend their kills from scavengers more fiercely than wolves and hide uneaten prey

Winter on the Northern Range Human hunters Provide large amounts of carrion in the form of gut piles on park borders during hunting season. Bears in hibernation cannot take use this Scavenging coyotes have difficulty finding the gut piles and are often shot by human hunters

QUESTION As global temps increase, what will happen to the snow depth and snow season? How will this affect the elk population? How will this affect the availability of carrion? Can wolves act as a “buffer” against climate change by delaying the detrimental effects of declining snow cover such that other species have more time to adapt to their changing environment?