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The Dilution Effect

How Biodiversity Can Affect Human Health

Co Authors:

Claudia Stein
Department of Biology and Tyson Research Center
Washington University in St. Louis

Eleanor A. Pardini
Environmental Studies
Washington University in St. Louis


In this case study students are provided with information for piecing together the story of how forest fragmentation and biodiversity loss can affect the risk of Lyme disease transmission to humans. The case introduces the dilution effect, a widely accepted theory—and one of the most important ideas in disease ecology—which suggests that disease risk for humans decreases as the diversity of species in an area increases. It also explains how landscape fragmentation, one of the most common threats to biodiversity, can influence the risk of Lyme disease for humans. Students interpret and discuss various figures to develop a concept map that connects all the individual results of the story. Students gain an appreciation for the complexity of species interactions in an ecosystem, the effects of forest fragmentation on these interactions and the possible consequences for human health. This activity was developed for an undergraduate introduction to environmental sciences course under the topic of biodiversity and conservation, but would also be suitable for interdisciplinary studies interested in examining the connections between conservation and public health.

  • Read and interpret scientific graphs.
  • Work productively and collaboratively in a team.
  • Use research results to develop a model of how the loss of biodiversity might influence human health.
Keywords: dilution effect; forest fragmentation; landscape fragmentation; Lyme disease; tick; biodiversity; human health; conservation
Topical Area: N/A
Educational Level: Undergraduate lower division, Undergraduate upper division
Formats: PDF
Type/Method: Discussion, Jig-Saw, Student Presentations
Language: English
Subject Headings: Ecology   Environmental Science   Public Health   Wildlife Management  
Date Posted: 8/15/2016
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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