Invasion and persistence were estimated under a number of conditions of population size (N0), infectious period (1/γ) and transmission rate (p), where for each combination of conditions 1000 simulations were run. While we modelled changes in population density for each combination of parameters, we also assessed the effect of population size because this is expected to affect the probability for the infection to disappear from the population, independent of density. In order to ensure that we here implemented the effects of population size and not density, population density N/A was calculated assuming that the area occupied when initial population size N0 = 100 is 1 ha, and that area increases linearly with increasing values of N0 (i.e. when initial population size increases, area also increases). This, for example, means that while population density fluctuates seasonally in exactly the same way for N0 = 100 and N0 = 1000 (or any other N0), the former assumes an occupied area of 1 ha and the latter an area of 10 ha. Because transmission events are stochastic, the size of the occupied area can have important consequences for virus invasion and persistence.