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

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Abstract:

Aim

The aim of this work is to provide a parsimony analysis of the Galapagos terrestrial vertebrates to understand their origin and relationships within 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 km2), six smaller islands and over 40 islets that have official names. Other small rocks 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 Scalesia land plant species were compiled from various published and online works. Parsimony Analysis of Endemicity (PAE) was used to find the most parsimonious cladograms depicting the biogeographic relationships of Galapagos to the American continents and the intra-archipelago ones. Analyses of species richness vs. island extents, species sharing vs. distance between islands, and species sharing vs. island extents were performed to assess the distribution patterns of the analysed vertebrates.Results

Genus distribution-based PAE results suggest that Galapagos archipelago 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 relationships 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 output shows that large islands cluster together, very small islands are placed with lesser confidence because of ecological noise explained by the analyses of species richness vs. extent, shared species vs. distance between islands, and shared species vs. extent relationships. This distribution-based work supports previously published phylogeny-based biogeographic analyses and corroborates them with an independent evidence. Two competing colonization models of the archipelago are discussed.

Keywords: American continents; Galapagos; island biogeography; land birds; land plants; parsimony; reptiles

Document Type: Miscellaneous

Publication date: April 1, 2001

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