Wolf Case Study:

Reintroduction of a native species: Wolves in Yellowstone


Thousands of Gray Wolves used to roam the Rocky Mountains before being slaughtered to near extinction in the 1930’s.  As the west was being settled and land used for grazing cattle, the wolves were considered a nuisance and threat to the livestock industry.  After being extirpated from most of their historical range throughout the United States, the gray wolf was placed on the Endangered Species list in 1973.  In 1995, Gray Wolves were successfully reintroduced to the Yellowstone Basin, and their population size is growing.  In 2003, they were downlisted from an “endangered” to “threatened” species.  Scientists studying the ecosystems of the Yellowstone Basin have since found strong evidence that wolves are a keystone species in this region.


General: all groups have the same questions:

1. Compare the terms ecosystem, community, species, and population as they relate to ecology.
2. What is the difference between exponential and logistic growth? What are some density-dependent factors that keep populations from growing exponentially indefinitely? What are some density-independent factors?
3. What is an ecological niche? What happens when two species have identical niches? How does the fundamental niche differ from the realized niche?
4. Explain an example of resource partitioning, and explain how natural selection can lead to character displacement.
5. Describe an example of each of the three types of symbiosis discussed in your text.
6. Explain how energy moves through the living components of an ecosystem (starting with primary productivity and including a discussion of food webs and ecological pyramids).
7. Explain how water, carbon, and nitrogen cycle through ecosystems, and give at least one example for each of how human activities can alter the cycle.
8. Seven different biomes are described in your textbook. If you were in charge of global ecosystem conservation but were told you had to focus all of your resources on preserving two of the seven types of biospheres, which would you choose, and why?


Questions specific to this case study:


5. Describe the history of the Gray Wolf in the western United States. When and why did it face extinction? When did reintroduction begin? Describe the current population size(s) and status.


6. What is a trophic cascade? Do research to find out about two trophic cascades that have been studied in nature, and provide a brief overview of each. Why is it important, in the context of preserving ecosystems, that we understand trophic cascades?


7. Describe the meaning of the term “keystone species” and summarize the evidence in the Yellowstone region that supports the idea that wolves fit this definition.


8. What other species found in the Yellowstone basin qualifies as a keystone species? Explain your answer, and relate it back to the importance of the wolves in this system.


9. Describe recent (in the last few months) legislation that will influence the spread of gray wolves through their native habitat.