THE ISSUE

Elimination of top predators (e.g. wolves) from regions like the Greater Yellowstone Ecosystem leads to changes in prey population density and behavior, as well as overall community structure. This issue addresses how ecosystems change when predators are removed, and what happens in such a system when the predators are restored. It is designed to address students' misconception that predators only influence ecosystems directly through predation. In the Greater Yellowstone Ecosystem, wolves exert impacts not only on their prey (elk) but also on lower trophic levels (e.g. willows).

ECOLOGICAL CONTENT

predation, trophic cascades, keystone species, direct vs. indirect effects, top-down vs. bottom-up effects, predator control, predation risk, prey behavior

STUDENT-ACTIVE APPROACHES

pairs share, hypothesis development, informal group work

STUDENT ASSESSMENTS

formulate hypotheses, essay quiz, minute paper, and concept map

AUTHOR

Cynthia Dott

Department of Biology, Fort Lewis College, Durango, CO 81301 Dott_C@fortlewis.edu

ACKNOWLEDGMENTS

This figure set was developed for Bio 220 at Fort Lewis College, and was improved by input from students in that course. Use of teaching examples of this sort was inspired by mentors like Diane Ebert-May, as well as other TIEE Issues Figure and Data sets. The exercise was improved by the helpful comments of Erin Lehmer, the TIEE Issues Editor Charlene D'Avanzo, and two anonymous reviewers.

CITATION

Dott, Cynthia. January 2009, posting date. Of wolves, elk and willows: how predation structures ecosystems. Teaching Issues and Experiments in Ecology, Vol. 6: Issues Figure Set #2 [online]. http://tiee.ecoed.net/vol/v6/figure_sets/trophic_cascades/abstract.html