Classroom Resources: Ecosystems Unraveling

By William Stolzenburg
January-March 2008 / Vol. 9 No. 1

Discussion Questions

In your own words, describe what is meant by “top-down” and “bottom-up” ecosystem dynamics. Why is the former referred to as “trophic cascades”? Are these two apparently contrasting views mutually exclusive?
Why did Lago Guri provide an especially useful study site for investigating trophic cascades?
Why did John Terborgh believe that evidence from Lago Guri contradicted predictions of the equilibrium theory of island biogeography? Why would this have important conservation implications?
If the notion of trophic cascades is an accurate reading of how ecosystems work, how might this idea inform conservation strategy? What sorts of ecological restoration might be appropriate in North America or elsewhere?

Websites for Further Information

The Rewilding Institute: http://www.rewilding.org/TopDownRegulation.html
Trophic Cascades Project, Oregon State University: http://www.cof.orst.edu/cascades/

Peer-reviewed Literature (in addition to the citations listed in the article)

Carpenter, S.R., J.F. Kitchell, and J.R. Hodgson. 1985. Cascading trophic interactions and lake productivity. BioScience 35: 634-639.
Estes, J.A. and J.F. Palmisano. 1974. Sea otters: their role in structuring nearshore communities. Science 185: 1058-1060.
Hairston, N.G., F.E. Smith, and L.B. Slobodkin. Community structure, population control and competition. American Naturalist 94: 421-425.
Ripple, W.J. and R.L. Beschta. 2004. Wolves, elk, willows, and trophic cascades in the upper Gallatin Range of Southwestern Montana, USA. Forest Ecology and Management 200: 161-181.
Terborgh, J., L. Lopez, and J. Tello S. 1997. Bird communities in transition: the Lago Guri Islands. Ecology 78:1494-1501
Terborgh, J., J.A. Estes, P. Paquet, K. Ralls, D. Boyd-Heger, B.J. Miller, and R.F. Noss. 1999. The role of top carnivores in regulating terrestrial ecosystems. Chapter 3 in M.E. Soulè and J.Terborgh, eds. Continental conservation: scientific foundations of regional reserve networks. Island Press, Washington, D.C.

Key Concepts