Living at the limit in a major biogeographical crossroad. The flora of the Pyrenean Mountains

Mountains shelter high biological diversity and constitute important barriers for species distributions. They often contain sets of species whose populations occur at their range limit (peripheral species), which according to the “Centre-Periphery” hypothesis are expected to perform worse and be more vulnerable than in central positions. Our study investigates this hypothesis by examining the potential vulnerability (abundance and ecological characteristics) of the flora of the Pyrenees, a major biogeographical crossroad containing a large proportion of the total European plant diversity. We also assess the contribution of peripheral plants in lists of conservation. We compared regional area of occupancy, local abundance, elevation, habitat and soil type preferences, of more than 2,600 central, peripheral and endemic native vascular plants of the Pyrenees mountains. Their conservation status was also assessed at different spatial scales. A quarter of Pyrenean species are at their distributional limit. Like endemics, peripherals have lower continental and regional occupancy than central ones, but their local abundance does not differ significantly. Endemics and peripherals are also more likely to be soil specialists at high elevation, mainly in (sub)alpine grasslands and rocky areas. Although occurring in different ecological conditions, peripheral species at their rear-edge (mainly Boreoalpine and Eurosiberian) tend to be more widespread regionally but equally abundant locally than leading- edge species (mainly Mediterranean). Peripheral taxa constitute a large portion of Pyrenean species protected at different geographic or administrative scales (31-56%), of highest importance in the Pyrenean red list. Peripheral species show contrasting ecology at the leading- and rear-edge, contribute substantially to the high plant diversity of the Pyrenean biogeographical crossroad and to the lists of priority species for conservation. Integrative biogeographical assessments of the rarity and ecology of mountain floras provide a better overview than administrative ones to establish priorities for conservation.OPCC-POCTEFA EFA (235/1) and VULBIMON (CGL2017-90040-R).Peer reviewe