Biodiversity and Lyme disease: dilution or amplification?

Reduced Lyme disease risk by the 'dilution effect' is often cited as an example of biodiversity providing 'ecosystem services' to public health. Using a mechanistic model we investigated how transmission of the Lyme disease agent, Borrelia burgdorferi, by Ixodes scapularis ticks amongst highly efficient reservoir mice is affected by varying the abundance of a less efficient reservoir host. Simulations indicated either amplification or dilution may occur, with the outcome depending precisely on mechanisms of competition, host contact rates with ticks, and acquired host resistance to ticks. Quantifying these mechanisms will be crucial to predicting how biodiversity affects Lyme disease risk.