Magnitude of the step in neutral allele frequency between the two patches (Δ p ) plotted against r / s for different strength of the barrier. Barrier strengths (m
) are indicated above each curve. The rectangle indicates the parameter space that could explain the results observed at the EF1α gene in M. edulis, and the dot shows the corner of that space which corresponds to the smallest barrier strength required. Results from a linear one-dimensional stepping-stone model with p0 = 0.0001, m = 0.3. Two hundred demes were used with a barrier to the right of deme 100.