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The Wolf, the Moose, and the Fir Tree

A Case Study of Trophic Interactions


Gary M. Fortier
Department of Animal Biotechnology and Conservation
Delaware Valley College


In this analysis case, students study predator-prey dynamics in the Isle Royale National Park ecosystem drawing on data and findings from the article “Wolves, Moose, and Tree Rings on Isle Royale” by B.E. McLaren and R.O. Peterson published in 1994 in Science magazine. The case was developed for a sophomore ecology class.  It could also be used in environmental science courses.

  • Evaluate trophic level interactions
  • Determine whether predators can control prey populations.
  • Determine the relationship between primary productivity and plant growth.
  • Understand how primary productivity may be measured indirectly.
  • Understand how ecological parameters, such as plant growth rates, may be measured indirectly.
  • Interpret graphical data.
  • Identify unstated assumptions.
  • Identify confounding effects from multiple factors.
  • Produce testable predictions from hypotheses.
  • Use data to support or refute competing hypotheses.
  • Determine limitations imposed by experimental design.
  • Assess the use of correlations in hypothesis testing.
Keywords: Trophic cascade; predator-prey dynamics; wolf; wolves; moose; tree rings; island ecology; experimental design; Isle Royale National Park; Michigan; Minnesota
Topical Area: Scientific method
Educational Level: High school, Undergraduate lower division
Formats: PDF
Type/Method: Analysis (Issues), Journal Article
Language: English
Subject Headings: Ecology   Environmental Science   Forestry   Botany / Plant Science  
Date Posted: 10/21/02
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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Supplemental Materials

The supplemental material below may be used in conjunction with this case.

  Click-and-Learn: Exploring Trophic Cascades hhmi/
Trophic cascades refer to impacts that reach beyond adjacent trophic levels. This interactive walks students through the classic example of sea otters in the kelp forest ecosystem off the west coast of North America. Students then apply their knowledge to predict responses and consequences of ecosystem changes in four other case studies. The case studies demonstrate how indirect effects mediated by changes in one species can broadly alter many aspects of community function. Produced by HHMI BioInteractive.


The following video(s) are recommended for use in association with this case study.

  Some Animals are More Equal than Others hhmi/
This short film opens with two questions: "So what determines how many species live in a given place? Or how many individuals of the species can live somewhere?" The research that provided answers to these questions was set in motion by key experiments by ecologists Robert Paine and James Estes. The film discusses Paine's starfish exclusion experiments on the coast of Washington state as well as Estes' and colleague John Palmisano's discovery that the kelp forest ecosystems of the North Pacific are regulated by the presence or absence of sea otters, which feed on sea urchins that consume kelp. These early studies were the inspiration for hundreds of investigations on other keystone species and trophic cascades, as well as ongoing studies into the regulation of population sizes and species numbers. Running time: 19:29 min. Produced by HHMI BioInteractive.

  Film Guide for "Some Animals are More Equal than Others" hhmi/
Film guide as well as instructor materials and a student quiz that complement the film "Some Animals Are More Equal Than Others: Trophic Cascades and Keystone Species." Produced by HHMI BioInteractive.

Thanks for this great case. I use this in IB biology in the topic of ecology. It is challenging and the students need guidance at this level, but the challenge with interpreting data is very useful and pertinent.

Christian Moore


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