Predator-Prey Interactions -- Modeling the Number of Fishers and Porcupines in New Hampshire

Ben Steele
Colby-Sawyer College
New London, NH
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project


In this Spreadsheet Across the Curriculum activity, students build an Excel spreadsheet to model the interaction between populations of a predator and a prey, in this case, porcupines and fishers. They use a simplified version of the Lotka-Volterra equations and generate graphs showing population change. They predict the results of changing the variables and then see the results by simulation. Finally, the students investigate a phase plane graph, showing population cycles of both species, and they interpret different parts of the graph.

Learning Goals

Quantitative goals:
  • algebra (interpreting equations, difference equations)
  • graphs (X - Y scatter plots, time series, phase plane, scale of axes)
Context goals:
  • modeling
  • Lotka-Volterra equations
  • interaction between predator and prey populations
Spreadsheet goals:
  • determining cell equations
  • absolute cell reference
  • graph design

Context for Use

This module is used in an introductory ecology class. Students are not expected to know calculus, so we use difference equations instead of differential equations in the simulation. Students should have some familiarity with Excel, although explanatory hints are included.

Description and Teaching Materials

PowerPoint SSAC2006.QH540.BS1.1-student version (PowerPoint 302kB Dec20 06)

The module is a PowerPoint presentation with embedded spreadsheets. If the embedded spreadsheets are not visible, save the PowerPoint file to disk and open it from there.

This PowerPoint file is the student version of the module. An instructor version is available by request. The instructor version includes the completed spreadsheet. Send your request to Len Vacher ( by filling out and submitting the Instructor Module Request Form.

Teaching Notes and Tips

The module works best in a small class or with several roving tutors to help students. It could probably be done as homework, but is designed for in-class use. Each student or pair of students will need a computer.


Students are directed to complete an assignment at the end that tests understanding of the key concepts. Answers can be compared to similar questions in the pre-test that is included in the instructor version.

References and Resources

Lynx and snowshoe hares in the Boreal forests of Canada: CBC Television - The Nature of Things - Walking with Ghosts