Biogeography of the Antilles based on a parsimony analysis of orchid distributions

Aim We obtain biogeographical patterns based on the distributions of shared orchid species of the Caribbean. These patterns are used to define biogeog raphical zones. We then analyse the concordance between the distributional patterns with ecological and physical features of the islands. Location We use orchid species recorded on 49 islands of the Greater, Lesse r, and southern Antilles, and the Bahamas. Three continental areas are incl uded: Florida (North America),, the Yucatan (Central America), and the Guia nas (South America). Methods We use a parsimonious analysis of species distributions that produc es the best arrangements of shared taxa among areas. The analysis uses 356 shared orchid species of the 863 species recorded for studied areas. The me thodology has been used to infer historical relationships among areas but w e interpret the results as static or ecological patterns of biogeographical affinities. Results Two kinds of island groupings are revealed. (1) Groups with common geology and geomorphology: the Bahama Archipelago, the Virgin Islands, the Cayman Islands and the southern Dutch Antilles. (2) An aggregation of dista nt islands with a heterogeneous geology but a common physiography: the Grea ter Antilles/Trinidad/ Lesser Antilles/Margarita-Tobago. The Guianas are li nked with the Greater Antilles, while the Yucatan and Florida are linked to the Bahamas. Main conclusions Groupings of islands are congruent with their gross ecolog ical features either from similar geomorphology or common physiography. The strong affinity among islands considerably distant among each other is exp lained by the high vagility of dust-seeded orchids. Then, floristic affinit ies seem determined by ecological characteristics of islands rather than by dispersal barriers. We predict that other plant groups with dust-like dias pores and animals with good vagility should show comparable biogeographic p atterns, Parsimony analysis of distributions (PAD) is an alternative method ology to multivariate analysis to compare biotas, and a graphic complement to quantitative methods producing numerical values.