Working with Brian Allan from the University of Illinois at Urbana-Champaign and Charles Drost from the U.S. Geological Survey's Southwest Biological Science Center, Orrock mined an existing dataset, collected on the Channel Islands shortly after the Four Corners outbreak, to look for relationships between biological and physical island characteristics and the prevalence of Sin Nombre on each of the eight islands.
The researchers found that 79 percent of the variation in disease prevalence among the islands could be explained by a single factor average annual precipitation. Adding in the physical characteristics of the islands and the number of predators accounted for 98 percent of the variation. Higher infection rates among Channel Island deer mice were strongly associated with more precipitation, larger island area and fewer predator species.
The strong effect of precipitation levels highlights potential links between changing climate regimes and human health. The results also suggest that more diverse predator populations could help keep animal-borne diseases in check an important lesson as top predators like wolves and bears increasingly disappear from ecosystems due to habitat loss and conflicts with humans.
The authors note that future studies should use experimental methods and examine larger systems to evaluate the generality of the observed patterns. Nonetheless, the strength of the associations they found on the Channel Islands is striking.
"What's shocking about these data is how tight the relationship is," Orrock says. "Rarely in ecology do you find that one variable will explain 79 percent of the variation in anything. The fact that precipitation does here, and that adding the effects of predator richness and island characteristics explains nearly all the variation in disease prev
|Contact: John Orrock|
University of Wisconsin-Madison