Figure 4.

Evolution of the impact of the parasite with the number of fragmentation events (F) experienced by the population. Variables are estimated over 8-year period starting 2 years after the last fragmentation event (t=10F+2) and ending at the beginning of the next one (t=10F+10). The initial 2 years of the period are omitted to discount fluctuations arising from fragmentation of the population; (a) evolution of the impact of the pathogen in relation to the number of fragmentation events (x-axis). For each replicate, the impact of the pathogen is calculated by the total number of dead individuals (from mild or severe disease) during the 8-year period, divided by the mean size of the entire population over that same period; (b) mean time before extinction (solid line) and re-introduction (dashed line) of the pathogen after F fragmentation events (x-axis). Extinction times above 1200 months (100 years) are described as more than 1200. For such values, local extinction within 10 years becomes very unlikely (as in (c)). Extinction and re-introduction times are calculated using specific methods detailed in the electronic supplementary material; and (c) proportion of disease-free subpopulations (solid lines), of unoccupied subpopulations (i.e. where the host species has become extinct, dotted lines) and of disease-free metapopulations (dashed lines) during the 8-year period following the Fth fragmentation event (x-axis). The probability of extinction of the entire metapopulation is calculated for each replicate as the number of times during the 10-year period when the entire metapopulation is extinct, divided by the number of months (n=96) within the period. The same formula applies to the cases of subpopulations where the empty/full state of the metapopulation is replaced by the proportion of subpopulations where at least one individual is infected (mildly or otherwise).