Evidence of the Dilution Effect: Biodiversity in Forest Communities Reduces Endoparasite Infection of Mammalian Hosts

Science Center A154

The precipitous decline of global biodiversity, coupled with an increase in infectious disease spread, has led disease ecologists to propose hypotheses that explain the ecological factors influencing disease transmission. One of the best-known of these hypotheses is the Dilution Effect, which suggests that biodiversity protects against disease by diverting parasites from competent to incompetent reservoir hosts. Though widespread and well-known, the validity of the Dilution Effect is highly debated, and critics often argue that it fails to consider additional ecological factors that may influence disease transmission. With its long history of disease studies in Peromyscus mice, Mountain Lake Biological Station (MLBS) is an ideal system to study the effects of host species richness on the parasite loads of mice and other small mammals. Over the course of 10 weeks, I analyzed the fecal samples of small mammals at sites across MLBS and tested for correlations between biodiversity and infection levels.Additionally, I explored the effects of anthelmintic medication of mice on the infection levels of other mammals, and I measured habitat characteristics to look for covariates with overall infection prevalence. These data revealed a significant negative correlation between species richness and infection intensity of mice, indicating that more specious sites had lower infection levels.Furthermore, anthelmintic treatment of mice decreased the infection intensity of other mammals, indicating that mice are an important contributor to the host community’s parasite pool. Finally, habitat data (driven mostly by percent of rock and log cover) is strongly correlated with overall infection prevalence, suggesting the possible influence of habitat characteristics on disease transmission. These results demonstrate broad support for the Dilution Effect, and provide an impetus for further examination of this hypothesis to better understand the relationship between habitat conservation and disease risk in natural systems.