PARENT SESSION
Oral Session #89: Biodiversity and Ecosystem Function III.
Presiding: R. Washington-Allen
Thursday, August 8. 1:00 PM to 3:45 PM. Coconino Meeting Room, TCC.

Health protection as an ecosystem function: biodiversity, tick-host interactions, and Lyme disease risk.

LoGiudice, Kathleen^*,1, Ostfeld, Richard¹, Keesing, Felicia^1,2, Schmidt, Kenneth^1,3, ¹ Institute of Ecosystem Studies, Millbrook, NY² Biology Department, Annandale-on-Hudson, NY³ Biology Department, Williamstown, MA

ABSTRACT- We report on our continuing effort to explore the effect of biodiversity on Lyme disease risk via the conceptual and mathematical models of ′The Dilution Effect′. The models predict that high species diversity in the community of vertebrate hosts for disease vectors dilutes the impact of the most competent reservoirs for the disease agent and reduces disease transmission. In the Lyme disease system, the main vector is the blacklegged tick and the principal natural reservoir is the white-footed mouse. The Dilution Effect predicts that a diverse assemblage of tick hosts reduces the proportion of ticks feeding from mice, resulting in lower infection prevalence in the tick population. We collected data (tick burdens, feeding success, and infectivity) from virtually every host in our site in southeastern New York and calculated the relative contribution of each host to the total infection prevalence. As new host species are added to a species-poor community, infection prevalence declines. To function as a ′dilution host′, a species must feed a substantial portion of the tick population and have a low probability of infecting ticks with the Lyme disease pathogen. Tree squirrels have the highest dilution potential, reducing infection prevalence by almost 58 percentage points from what it would be if ticks were feeding on mice alone. Other hosts, such as songbirds and skunks, occur at too low densities and/or host too few ticks to function as effective dilution hosts. Some common tick hosts, such as shrews, serve not only as dilution hosts, but also to maintain the spirochete in the community when mouse density is low (′rescue hosts′). Our research provides new incentives to preserve high vertebrate biodiversity in Lyme disease endemic areas and underscores the importance of understanding community interactions in disease ecology.

KEY WORDS: rescue effect, dilution effect, reservoir competence, vector-borne disease