**3. On the Galápagos biogeography**

The Galápagos Islands represent a strategic geographic zone in the planet to carry out studies on biodiversity, speciation, adaptation, ecology and dispersion of species belonging to different kingdoms. In an attempt to explain the current biogeography of the islands, a number of studies have been done since the Darwin's times in the 19th Century [12-14].

It is well known that the islands geological origin is oceanic, while the origin of its biota is continental [15]. The studies on the Galapagos Islands' biogeography and evolution were predominantly (if not exclusively) focused on macro organisms: there is a marked shortfall in the knowledge of microbial populations, communities and biodiversity in the Galapagos Islands.

Standard biogeographic tracks link the archipelago of Galápagos with Central America, western North and South America, the Caribbean, Asia and Australasia [14]. The Galápagos Islands community characteristics share the common features of the biota occurring in oceanic islands such as: disharmony, endemism and relictualism [16].

The archipelago of Galápagos is composed by oceanic islands where the terrestrial colonists such as plants, animals, and part of the microorganisms, should have crossed an oceanic barrier to reach the land. It means that the origin of the biota in this group of islands is entirely explained by the dispersal with no vicariant component, since the islands were never con‐ nected to the mainland by any land bridge or island chain [14]. Furthermore, since the Galápagos Islands are separated from the centers of origin of species in the mainland, there are abundant "empty" ecological niche spaces [17].

The colonization of the varied environments within the islands by yeast species must be primarily explained by the occurrence of colonizing terrestrial species of plants and animals that arrived to the islands as a sweepstake along the natural history of the archipelago. The sea water and marine fauna must have been other sources of colonizing yeasts species. Finally, the yeasts flora inhabiting the gut of insects associated to plants as well as birds and terrestrial vertebrates must have completed the cast of yeast diversity in the Islands.

Undoubtedly the strong association of plants and microorganisms must be regarded as a dispersion factor for microorganisms, including yeasts in the Galápagos. In 1976 [18] deter‐ mined that 236 species of vascular plants are endemic (representing 45% of total species); 155 species are from Neotropical origin (which represents 30% of the total species); 62 different species of vascular plants are from Pantropical origin (12% of total species); 61 species are originated in the Andes (representing 12% of total species); while only 4 and 2 species correspond to Mexico and Central America and non-tropical South America, respectively (2% of total species). This study takes into account the indigenous species of the archipelago, namely, those species that were not introduced by man's activities [18].
