Figure 1.

Schematic representation of two synergistic positive feedback cycles involved in epizootic plague eruptions, with emphasis herein on prairie dogs (PDs). Cycle A illustrates an increase in flea:host ratio, and Cycle B illustrates the breakdown of PD territoriality. As the two interconnected loops repeat themselves, and remaining PDs become more mobile, the hazard rate rapidly escalates for each remaining PD. Both loops feed into the transmission rates and ultimately into the plague-caused deaths that the two loops have in common (hence heavier arrows for the central parts of both loops).