Biogeographic relationships of the Galapagos terrestrial biota: parsimony analyses of endemicity based on reptiles, land birds and Scalesia land plants

Aim The aim of this work is to provide a parsimony analysis of the Galapago s terrestrial vertebrates to understand their origin and relationships with in the archipelago and to the American continents. Location The Galapagos archipelago is located 1000 km off the western coast of Ecuador. It is formed by 13 large islands (greater than 10 km(2)), six smaller islands and over 40 islets that have official names. Other small ro cks and islets remain unnamed. The archipelago straddles the equator at the 90th meridian west. Methods Lists of the living reptilian, land bird species and genera and Sca lesia land plant species were compiled from various published and online wo rks. Parsimony Analysis of Endemicity (PAE) was used to find the most parsi monious cladograms depicting the biogeographic relationships of Galapagos t o the American continents and the intra-archipelago ones. Analyses of speci es richness vs. island extents, species sharing vs. distance between island s, and species sharing vs. island extents were performed to assess the dist ribution patterns of the analysed vertebrates. Results Genus distribution-based PAE results suggest that Galapagos archipe lago was settled by South American reptiles. The Galapagos islands cluster with Ecuador, Chile and Peru. A large American clade including Meso-America , USA, Mexico and Colombia is supported by this work too. Sister group rela tionships between the Galapagos-western South American clade and the large American clade are not defined. Species distribution-based PAE results are not able to place the Galapagos into any clade. PAE intra-archipelago outpu t shows that large islands cluster together, very small islands are placed with lesser confidence because of ecological noise explained by the analyse s of species richness vs. extent, shared species vs, distance between islan ds, and shared species vs, extent relationships. This distribution-based wo rk supports previously published phylogeny-based biogeographic analyses and corroborates them with an independent evidence. Two competing colonization models of the archipelago are discussed.