The late Pleistocene endemicity increase hypothesis and the origins of diversity in the Canary Islands Flora

Aim We explore the idea that most pre-glacial non-endemic Canarian flora became endemic to the archipelago by the extinction of its mainland populations during the late Pleistocene glaciations, implying that the extant non-endemic flora is mostly post-glacial: the 'late Pleistocene endemicity increase hypothesis'. Taxon The native flora of the Canarian archipelago. Methods We statistically compare the distributions of 2087 Canarian endemic and native non-endemic plants across islands. We also carry out connectivity analyses using their dispersal paths, obtained by connecting all the islands of occurrence for each taxon. Results While the distribution of the endemic flora is strongly L-shaped (with a much higher proportion of Single-Island Endemics than Multiple-Island Endemics), that of the native non-endemics is U-shaped (i.e. similar prevalence of single-island taxa and taxa distributed on all islands). The native non-endemics have a significantly lower proportion of single-island taxa and a higher proportion of widespread taxa than the endemics. Most dispersal paths in the endemics connect the central and western islands, whereas they are extended across all islands in the native non-endemics. Main conclusions The contrasting distributional patterns of the endemics and the native non-endemics support an outstanding role of species diversification in the endemic flora, but a still negligible influence of the insular selective and stochastic pressures (including extinction) in the native non-endemic flora, arguably due to its recent origin. Our results suggest that the high endemicity levels of the extant Canarian flora can be explained by two complementary processes: (i) high diversification rates throughout the ontogeny of the archipelago, often from colonisers that attained a widespread distribution prior to speciation, and (ii) an 'endemicity increase' during the late Pleistocene glaciations, whereby most of the pre-glacial non-endemic Canarian flora became endemic due to the extinction of its mainland conspecific populations, thus emphasising the role of the Canaries as climatic refugia.