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

2. 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

3. 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

4. Timeline History of Gray Wolves in Yellowstone Park
1872 YNP is established by an act of the U.S. Congress
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.
Thirty-one wolves are reintroduced into YNP
wolves, in 130 verified packs, and breeding pairs.

5. Population Figures for Montana

6. 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.

7. Wolves as Keystones

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

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

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

11. 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

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

13. 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

14. 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

15. 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

16. 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.

17. 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.

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

19. 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

20. 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

21. 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

22. 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?