FACULTY NOTES

This figure set activity should be fairly brief. Usually students will predict that the elk population surged to much higher levels after wolves were extirpated from Yellowstone, and then dropped significantly when wolves were restored. (Note: Make sure the students make their predictions before they see the figure!) In some parts of the Greater Yellowstone Ecosystem there is evidence of major swings in the elk population, but this data set seems to show a steady and gradual decline in the elk population during the 20th century. This usually comes as a surprise to the students, because their expectation is of direct control by the predator on the prey population. This is a key time for some thought-provoking group discussion, in order to address the common misconception at the heart of this whole issue: that predator impacts are all direct, and never indirect. Some questions to help get a discussion started could include:

• If the wolves aren't "controlling" elk density directly, then why is there a rebound in woody vegetation after the wolves return?
• It appears as if wolves are reducing elk browsing in riparian habitats, but not by directly reducing elk numbers. How else might wolves be reducing elk browsing?

Try to get the class to brainstorm ideas, while you write them on the board. Resist the urge to critique their ideas or to say which are correct at this point. If you can't get students to speak up in the large group setting, have them "think-pair-share" with a partner, and then call on pairs to share their thoughts with the group. During this discussion, questions might also arise about the validity of the data, since some of the information is qualitative and not quantitative (students might think the numbers are "made up"). Ripple and Beschta (2004a) do a good job of showing that the evidence for the population trends shown in this figure is quite robust, even though not all of it is quantitative. For additional background on this topic, see the Methods section of their paper.

For assessment on this activity, have the students write a minute-paper addressing why their predictions about elk population dynamics were upheld or not. Alternatively, you could combine assessment for Figure sets 3 and 4 into one essay quiz, incorporating the questions from both exercises.