To simulate the Wv0 scenario in Figure 3 the supply of susceptibles is controlled to maintain the total population of infectives at a broadly constant level (i.e. resource availability constant). This reflects low-to-minimal growth rate (equilibrium, r small) of the incumbent. The number of infectives fluctuates around an equilibrium level and new variants attempt to invade the system whilst it is in this configuration. In this scenario the incumbent is already established at equilibrium, so we are addressing a global competitive situation. These simulations were run for 200,000 days with d(x)~a with a in the range +0:1 and with a mutation rate of 10 {4 day -1 .