Contrasting biogeography of endemic and alien terrestrial species in the Canary Islands

Endemics and alien organisms can be considered two faces of the same coin, since management of both groups of taxa have strongly interrelated conservation implications. Islands are rich in endemic species and are also very vulnerable to biological invasions. We analysed the biogeography and taxonomy of endemic and alien terrestrial species in the Canary Islands including fungi, lichens, bryophytes, vascular plants, arthropods, molluscs, annelids and vertebrates. By using the plant dataset we also tested the hypothesis that there is less taxonomic similarity between aliens and natives than between endemics and nonendemic natives. Although in the Canary Islands species richness of endemic species (28% of terrestrial flora and fauna) was higher than for alien species (3%), this trend was very much dependent on taxa and island. For example, more than half the annelids present in the islands are alien, and the flora of Fuerteventura has almost as many endemics as alien species. As hypothesized, for plants, there were more exclusively alien families (34) than families with only endemic species (5). Moreover, neither alien nor endemic plant species represented a random assemblage of taxa: most families with aliens were over-represented compared to the taxonomy patterns of the native flora, while for endemics almost the same proportion of families was over- and sub-represented compared to proportions of non-endemic natives.