Climate, soils, and connectivity predict plague epizootics in black-tailed prairie dogs (Cynomys ludovicianus)

Outbreaks of plague in wildlife are sporadic and spatially dispersed, and they depend on coincidence of susceptible hosts, flea vectors, the plague bacterium (Yersinia pestis), and environmental factors that support pathogen transmission. We fit spatial models of plague outbreaks to a long-term data set (1981–2005) of towns of black-tailed prairie dogs (Cynomys ludovicianus) on the shortgrass steppe of northeastern Colorado. We investigated the effects of spatial distribution (town area and connectivity to other prairie dog towns), climate (spring and summer precipitation and temperature), and soil moisture-holding capacity. In logistic regression models, plague epizootics were predicted by connectivity to other towns experiencing plague during periods with relatively low temperatures, in soils with high moisture-holding capacity. After accounting for connectivity between prairie dog towns and current-year climatic conditions, little additional spatial or temporal autocorrelation was detected. Spatial logit association models provided evidence for localized epizootic hotspots and that greater summer rainfall predicted plague events. Plague outbreaks were not predicted by precipitation in the previous year. As such, no evidence was found to support an indirect cascade model of plague outbreaks for black-tailed prairie dogs on the shortgrass steppe in Colorado. Instead, the models suggest that plague occurrence depends upon direct climatic effects on flea vectors and the plague pathogen.