1. Yellowstone National Park
Wolf Case Study

2. Wyoming’s Yellowstone

3. Species Interactions cause trophic cascades
Trophic cascade: changes in one level will create changes in other trophic levels.
Trophic Levels:
Tertiary Consumer
Secondary Consumer
Primary Consumer
Primary Producer/ plants
tertiary
consumers
secondary
primary
producers 5
5000
500,000
5,000,000

4. Food Web in Yellowstone
The wolves eat moose, pronghorn, mule deer, elk, bison, and bighorn sheep.
They share these prey (food) with other predators like: coyotes, mountain lions, and grizzly and black bears.

5. The wolves are a keystone species
Keystone species: they have an unusually large effect on the ecosystem.
In 1926 unrestricted hunting had eliminated the wolves from the park community.
In 1920 An annual census of elk was initiated by park managers.

6. Intervening in nature
From the park service selectively killed elk herds so they wouldn’t go over caring capacity.
In 1968 they stopped because of public pressure.
Once the killing stopped the elk population rapidly increased.

7. Effects of the increase in Elk
The elk eat aspen trees and once their population took off there were no more young trees.
The elk also severely browsed (ate) streamside willows and this didn’t allow beavers to eat or make dams.
The absence of beavers dams made less biodiversity because of loss of this habitat.

8. Everywhere else there were no elk, there were tree populations which told scientists it was due to the elk that trees were becoming depleted.

10. Bring Back the Wolves
In 1995 after the wolves had been gone for 70 years, park managers decided to bring some to the park again.
They had noticed that in the Lamar Valley, where they brought back the wolves that the tree problem began to go away and other things also became more established.

11. Lamar Valley in Yellowstone
Once the wolves were back the elk there avoided the aspen groves where wolves could easily attack them.
This allowed the tree population to increase and also allowed the beaver colonies to increase from one in 1996 to seven in 2003.
These beavers where then able to make dams and mini ecosystems for all other creatures that rely on them.
The presence of this one predator effected many trophic levels of the ecosystem.

12. Cause and Effect chain map for Yellowstone
Effect/ Cause
Main Cause:
1926 Hunting
Of wolves kills
them all off
Effect/ Cause
Effect/ Cause
Effect/ Cause
Effect/ Cause
Overall Effect: Loss of Biodiversity in Yellowstone

13. Conclusion Questions
1. Define what a keystone species is and give an example of one and why it is one?
2. Explain a trophic cascade?
3. Summarize what this case study was about? Analyze the data to help make your summary more in depth.
4. Compare and contrast this case study with the wolf and deer case study you did before.