Agricultural subsidies affect isotopic niche size in elk and white-tailed deer
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Agricultural crops are a food subsidy for wild ungulates that can bring animals into close proximity, facilitating disease spread. We used stable isotope analysis to reconstruct the diets of elk and white-tailed deer in three areas in the Canadian prairies and calculated their isotopic niche breadth. Isotopic niche breadth was greater for deer than elk, indicating that deer are a generalist species composed of individual specialists with varied diets, while elk are individual generalists. White-tailed deer niche breadth decreased with increasing consumption of agricultural foods in early fall, but not on an annual timescale. Elk niche breadth did not change with consumption of agricultural foods. Agricultural sources were 40-80% of the diets of both species in all areas. Agricultural feeding may increase the risk of disease in elk and deer not only by increasing their apparent density at feeding sites, but also by subsidizing increases to their overall density.