STUDENT INSTRUCTIONS

What are other ways that wolves could be affecting elk browsing, other than via direct population control? After brainstorming ideas with the rest of the class (in the previous section), you and your partner should join another pair to make an informal group of four. Study the three photo pairs in Figure 4 together, looking for differences and similarities in each pair.

• What patterns can you see in the woody vegetation (willows and aspen) in these photos?
• Where is there evidence of release from browsing pressure by elk, and where is browsing pressure still evident?
• What other differences might there be between sites that are still heavily browsed and sites that are not?
• Wolves are now present in all of these areas, and yet their impact on elk seems to be variable. How might elk behavior vary in the different kinds of sites shown in the photos?

After you have had a chance to discuss these questions and the trends shown in the photo pairs with your group, work together to create a flow chart of predator-prey encounters. Show how prey (elk) behavior and choice of foraging site might vary under conditions without predators (wolves) (i.e. Yellowstone National Park from 1926-1995), vs. with predators (i.e. Yellowstone after wolf restoration, 1995-present). Your instructor may show you examples of flow charts to give you an idea of how to get started.

As a companion to the flow chart, work with your group to construct two simple food chains showing the relationships among wolves, elk, and riparian plants in a system with and without wolves. Groups will be called upon to present their diagrams to the class for discussion, and your instructor will probably ask each group to turn in a copy of the three diagrams.

After more discussion of trophic cascades and indirect effects in food webs, your final (individual) assignment (probably as homework) will be to construct a concept map of the Yellowstone food web that shows the impacts of wolf removal on elk behavior, woody riparian plants, beaver (who rely on cottonwoods and willows as their main food source), migratory birds (who use the riparian forest as an important stop-over point and source of food), and stream channel functional health (stream banks are held in place by riparian vegetation, for example). If you have not already used concept maps to model the interactions in biological systems, your instructor will walk you through an example to give you an idea of how best to construct one.