Figure 5. Changes in the slope of the isolation-by-distance relationship following a linear stepping-stone colonization process.

Data were simulated in the program QuantiNemo (Neuenschwander et al., 2008) for 50 demes where, initially, only one edge deme was occupied. Colonization and migration took place only between neighbouring demes at a rate m (colonization rate and migration rate are equal). The carrying capacity of each deme was N = 1000, and newly established demes grew instantly to carrying capacity. We simulated 9 loci with a maximum of 7 alleles per locus, assuming a K-allele mutation model and a mutation rate of μ = 5*10⁻⁴. Initial allele frequencies were generated in the program Easypop (Balloux, 2001) to match the average number of alleles observed in our real data set. The recolonization process was completed within the first 50–70 generations. IBD was significant directly after colonization (after 100 generations) as well as at migration-drift equilibrium (after 10 000 generations). The graph shows that the observed steeper slope in type A could be explained by a lower migration rate and/or more recent colonization of the area.