Figure 3

Population divergence ( F _ST ) versus changing rates of gene flow ( Nm ) through time. Panels illustrate the effects of migration rates changing in different ways over time: (a) gene flow decreasing exponentially as two populations separate; (b) gene flow increasing exponentially as two populations come back into contact; (c) sudden increase in gene flow 10,000 years ago in the Holocene; and (d) sudden increase in gene flow 30,000 years ago in the Pleistocene. Black, blue and red lines reflect population migration rates (Nm) that change through time as described for each of the model scenarios listed above. These lines represent long-term gene flow averages (Nm) of 0.033, 0.33 and 3.3, respectively. Importantly, the total amount of gene flow does not differ between lines with the same color.