Network analysis by simulated annealing of taxa and islands of Macaronesia (North Atlantic Ocean)

Abstract

With the aim of explaining the role that taxa and island features have in biogeographical patterns, we processed presence–absence matrices of all the Macaronesian native species of ten different taxa (arthropods, birds, bryophytes, fungi, lichens, mammals, mollusks, pteridophytes, reptiles and spermatophytes) through simulated annealing analysis. Distribution patterns among the archipelagos were pinpointed, along with the different biogeographic roles played by islands and species groups. All the networks analysed resulted to be significantly modular and the structure of biogeographic modules reflects known past connections among the archipelagos and the current drivers of species distribution. The role assigned to the species supports some biological (ecological amplitude, degree of endemicity) and functional (long-distance dispersal and persistence abilities) traits of their respective biota and justifies their position in recent models of biogeographical distribution. Whereas it was expected that the modules identified by the spermatophytes and arthropods would reflect the compartmentalization of archipelagos quite well, this was also the case for much more vagile taxa, such as fungi or lichens. Conversely, results obtained for pteridophytes and bryophytes suggest that for those taxa geographic distance and/or macroclimatic conditions are less important than the size, age and orography of an island to determine the modularity of island groups. On the other hand, dry, species-poor islets, act as connectors, tending to cluster together for different taxa, independently of their archipelagic adscription, whereas large, high, humid islands tend to form network or module hubs representing regional centers of speciation and dispersal.