Precipitation levels and species biodiversity may affect humans' exposure to zoonotic diseases — those carried by other animals.

Hantavirus, which is carried by wild rodents, especially deer mice (Peromyscus maniculatus, pictured), causes severe lung disease in humans. The prevalence of the Sin Nombre variant of hantavirus, which is endemic in deer mice on California's Channel Islands, is affected by several ecological factors.

Credit: C. A. SCHWEMM

John Orrock at the University of Wisconsin, Madison, and his colleagues analysed data from the islands and found that increased viral prevalence was linked to greater precipitation and island area, and also to fewer predator species. Precipitation accounted for 79% of the variation in prevalence. Adding in island area upped this to 93%, and including predator richness took the total to 98%.

Am. Nat. doi:10.1086/659632 (2011)