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Eleanor A. Pardini
Lecturer and Assistant Director of Environmental Studies
Environmental Studies
Washington University in St. Louis
The Dilution Effect: How Biodiversity Can Affect Human Health

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.