FACULTY NOTES

Have students work in informal groups of about four, and study the photo pairs in figure set 4. They should discuss among themselves what the photographs are showing - that, in fact, it is elk behavior that is most strongly impacted by the presence of wolves, because of their fear of predation, which is greater in some habitats than in others. In this habitat, elk feel more threatened in the close confines of riparian areas, and feel safer (and therefore spend more time) in the more open uplands. The photos themselves are fairly straightforward, but less advanced students may need help in recognizing the significance of what is being shown here: the potential power of indirect effects in food webs.

Introduce the idea of flow charts to the class, so that groups can use the information gleaned from the previous figure sets and this last set of photos to construct their own chart showing how prey foraging behavior is likely to change in the presence of predation risk. Ripple and Beschta (2004b) include such a diagram in their paper - instructors may want to refer to it as a model, keeping in mind that students will come up with many variations, most of them equally valid.

Call on a few groups to draw their simple food chains and flow charts on the board for discussion purposes. Ask students to explain what makes some areas "high-risk" browsing sites, while others are "low-risk."

Follow this activity with a mini-lecture on indirect effects, predator-prey non-lethal vs. lethal effects, and trophic cascades. This is also a good opportunity to introduce the idea of top-down vs. bottom-up trophic cascades. Ask the class which type of cascade is shown in this ecosystem (it is a "top-down" cascade).

For the final assessment of this issue, assign as homework a concept mapping exercise (see electronic references in Resources section). Each student should construct their own concept map of the Yellowstone food web, showing the impact of wolf removal on elk behavior, woody riparian plants, beaver (which rely on cottonwoods and willows as their main food source), migratory birds (which 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). There are other components of the ecosystem that you could add (or remove) from this exercise; see Ripple and Beschta (2004b) for additional ideas.

If concept maps have not been used in the class previously, students will need to be taught how to make them by working through an example from a different natural system (perhaps from a topic you've addressed earlier in the course). General guidelines for grading a concept map are listed below in this loose rubric:

• Accuracy and Thoroughness. Are the concepts and relationships correct? Are important concepts missing? Are any misconceptions apparent?
• Organization. Was the concept map laid out in a way that higher order relationships are apparent and easy to follow? Does it have a title?
• Appearance. Was the assignment done with care showing attention to details such as spelling and penmanship? Is it neat and orderly or is it chaotic and messy?
• Creativity. Are there unusual elements that aid communication or stimulate interest without being distracting?

 (Adapted from http://www.udel.edu/chem/white/teaching/ConceptMap.html )

For advanced students, several good exam or quiz essay questions could come out of this exercise:

• Ask students to describe a (hypothetical) situation where the trophic cascade works from the "bottom-up."
• Ask students how the Yellowstone trophic cascade might be different if the strongest effect of wolves on elk was lethal instead of non-lethal.
• Ask students to construct a concept map showing the impacts of beaver removal on the Yellowstone ecosystem. (This would require additional background information about the role of beavers in riparian systems - and beaver ecology in general - look for primary literature on the WWWeb, using (e.g.) "Google Scholar.")