For all simulations, the recovery rate c was set to 0.1, the maximum probability of a visit to the hotspot, P max , was set to 0.1, and the BRW step length S was set to 0.25 (i.e., 1/4 of the distance between the center of neigbouring group's territories). We also assumed that the within-group transmission probability, P w , was at least ten times higher than the between-group transmission probabilities (P B and P T ). The model was implemented in Delphi 7 (Borland Software Corporation, 2002). Table 1 summarizes parameter definition and values, and a sample run of the model is shown in Video S1.