Biogeographical network analysis of plant species distribution in the Mediterranean region

Aim. We analysed the spatial distribution patterns of plant species, in order to characterize the biogeographical structure of the French Mediterranean flora. Location. South of France (Languedoc-Roussillon and Provence-Alpes-Cote d'Azur). Taxon. Vascular plants. Methods. We used a network approach to identify and characterize bioregions in southern France, based on a large database consisting in millions of geolocalized plant samples corresponding to more than 3,500 plant species. This methodology is performed following five steps, from the biogeographical bipartite network construction, to the identification of bioregions under the form of spatial network clusters, the analysis of their interactions and the identification of groups of plant species based on the species contribution to the biogeographical regions. Results. The French Mediterranean area is divided into eight statistically significant biogeographical regions that are highly connected spatially. Mediterranean and temperate sub-networks can be distinguished. The three mediterranean bioregions are share an important pool of species, and present a high spatial coherence. The limit formed closely matches the mesomediterranean thermoclimatic belt. The transition area between Mediterranean and temperate systems is represented by the bioregion "mediterranean border" whose northern limit fit the limit of the Mediterranean biome. Main conclusions. The proposed network approach provides a characterization of the biogeographical structure which confirms some previously recognized floristic regions in southern France, while providing more precise insights into the relationships between them. This approach sheds light on the historical and ecological mechanisms shaping the distribution of Mediterranean biota, and exemplify why fragmented distributions are common in the Mediterranean region.