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                                Figure 5.  Correlations between species occurrences (x-axis) and population genetic differentiation, Dst
                                (y-axis) for the species occurring on the studied islands. The colours indicate if a certain square is significantly
                                filled (blue), significantly empty (orange) or shows no significant difference compared to values obtained by
                                chance (white). All islands are significantly enriched in widespread species with low genetic variation, and most
                                are impoverished in rare ones.

                                a key biogeographic region. Similar comprehensive assessments of island communities are scarce, especially due to
                                the difficulty of acquiring high quality data at both faunistic and genetic levels for large groups of organisms 8,22,26,27 .
                                The evaluation of the contribution of singular factors in characterizing island diversity facilitated the identification
                                of species that deserve conservation consideration on individual islands. The composition of butterfly communities
                                and their genetic structure were shaped by neutral (frequency at source) and non-neutral (differences in dispersal
                                tendency among species, interactions generating chequered patterns) determinants. In particular, frequency at source
                                had a strong contribution in determining the occurrence of species on islands, as expected according to a neutral
                                hypothesis, but species dispersal tendency also played an important role and many sedentary species were rare on
                                islands despite their ubiquitous presence on mainland and Sicily (M. jurtina, C. pamphilus, P. aegeria, P. cecilia and
                                Aricia spp.
                                   One of the main findings of this study, stemming from the community and genetic data, is that even in a rela-
                                tively restricted area, island populations have very different histories and are subjected to different re-colonization

         Scientific RepoRts | 6:28828 | DOI: 10.1038/srep28828                                                 6
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