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Building a More Intricate Web

A Reexamination of Trophic Levels


Sarah A. Orlofske
Biology Department
University of Wisconsin–Stevens Point


This case study follows two beginning undergraduate researchers on a quest for a summer research project related to food web ecology. While writing their research proposal, the students receive feedback indicating that they have neglected an entire group of organisms from their food web—parasites, which leads them to a scientific research paper discussing how these organisms have been overlooked by scientists studying food webs, the challenges involved with including parasites in food webs, and the contributions parasites ultimately make to food webs. An integrated activity in which students visualize the food web using images of organisms and answer questions about species interactions provides opportunities to examine key concepts such as omnivory, ontogenetic diet changes, trophic levels, complex life cycles, and taxonomic aggregation. This case study was originally written for an undergraduate general ecology course, but could easily be adapted to undergraduate general biology courses covering community ecology or specific courses in invertebrate zoology, parasitology, or disease ecology. The teaching notes also discuss how the included code for R statistical computing software can be used to extend the case study in a more quantitative direction if desired.

  • Analyze the types of relationships represented by food webs, including predator-prey interactions as well as those previously overlooked such as parasitism.
  • Explore various research-based methodologies for examining species interactions and incorporating them into food web construction.
  • Apply typical food web terminology (primary producer, primary consumer, secondary consumer, tertiary consumer, carnivore, herbivore, omnivore) to a partial food web based on empirical scientific research.
  • Examine the role of complex life cycles, omnivory, and cannibalism in food webs.
Keywords: Food web; community ecology; parasite; aquatic ecology; species interactions; network models
Topical Area: N/A
Educational Level: Undergraduate lower division, Undergraduate upper division
Formats: PDF
Type/Method: Interrupted
Language: English
Subject Headings: Biology (General)   Ecology   Limnology   Zoology  
Date Posted: 7/29/2018
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.

Teaching Notes

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Answer Key

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Supplemental Materials

This case includes an optional extension for R statistical computing software that makes use of the following files (see teaching notes for further details).


  Free_Community Zip file
  Total_Community Zip file
  Freeliving.csv Spreadsheet file
  Parasite.csv Spreadsheet file
  MissingTrophicLevel_V3.R Script file

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