Does interspecific diet overlap contribute to the spread of chronic wasting disease?

Background/Question/Methods

Diet overlap can bring individuals from different species into close proximity with one another, providing opportunities for diseases to spread between them. Elk (Cervus canadensis) and white-tailed deer (Odocoileus virginianus) are two large herbivores with generalist diets. Populations of these species are valued for hunting and wildlife viewing opportunities but they also damage agricultural crops and act as reservoirs for diseases that harm other wildlife, domestic animals, or their own populations. Chronic wasting disease (CWD) affects both species in Saskatchewan and is thought to spread when animals are in close proximity, such as at shared food sources. Our objective was to quantify the diet overlap between elk and white-tailed deer in two areas in Saskatchewan with different levels of CWD and test the effect of shared food sources on the spread of wildlife disease. We measured the carbon and nitrogen stable isotope ratios of hair and muscle tissue for both species in areas of high and low CWD prevalence, and then compared the area of standard ellipse overlap and mean distance to centroid. A higher area of standard ellipse overlap and lower mean distance to centroid indicates more diet overlap, which we expected to find associated with higher CWD prevalence.

Results/Conclusions

Contrary to our expectations, we found a smaller area of standard ellipse overlap and greater mean distance to centroid in the study area with higher prevalence of CWD. It is possible that niche partitioning restricts the spread of CWD to only one species, or that the interspecies diet overlap does not contribute to the spread of CWD. We are currently measuring the stable isotope ratios of wild and agricultural plants collected from these study areas in order to reconstruct the diets of both species and identify significantly overlapping diet components and resources used exclusively by one species.