Fig. 2

Graphical representation of island and stepping stone migration models (IS and SS) in the panel above. Black rows represent the presence and direction of migration rates among populations (purple circles). The panel below represents two examples of simulated global patterns, where a set of 100 pairs of coordinates are picked from a set of 1000 random pairs of coordinates built in 2D squares at different scales (in the example here reported the scales are 1:10,000 and 1:100,000, respectively). Every 25 pairs of coordinates are assigned to a different simulated population, distinguished by red, blue, black and yellow colors, in order to obtain spatially segregated populations. These simulated spatial distributions are used to calculate the matrix L of spatial connection (see Additional file 3: Figure S1)