Fig. 4

Neighbour joining cluster analyses (Sørensen dissimilarities) based on the occurrence of 78 species within 17 areas (A–S) as defined in Fig. 2. Trees are unrooted (a), rooted in the Po Plain (b), and in southern Sicily (c). Numbers show the percentage of bootstrapped trees (1,000 replicates) corroborating the focal split. Colours link sections consistently clustering together. The dark red square is highlighting the closest link of Sicily (M, N, O), which consistently is Sardinia and Corsica (P, R, S). The order of areas best matches the latitudinal mainland gradient