Food limitation at species range limits: Impacts of food availability on the density and colony expansion of prairie dog populations at their northern periphery

Understanding limiting factors affecting population growth for imperilled species is crucial for conservation and management. This research investigates whether black–tailed prairie dog (Cynomys ludovicianus) populations are food limited on their northernmost range extent. We measured background vegetation rates and used food supplementation in a ‘before–after–control–impact’ (BACI) design to test whether increased food positively impacted prairie dog population density and colony expansion. Experimental results did not support food limitation. Overall, density increased from 2008 to 2009 but remained relatively similar between control and treatment plots. Correlations between natural, non-supplemented vegetation biomass and prairie dog density suggest that natural food availability in 2008 may have driven population growth into 2009. Natural food availability was highly variable among years and prairie dog densities may be impacted by food scarcity in some years but not others. Colony spatial expansion was greater in the absence of food supplementation, suggesting food scarcity may drive colony expansion. This research has important implications for the conservation and management of prairie dogs and species that depend on them such as reintroduced black–footed ferrets (Mustela nigripes) in Canada and other populations across their range.