Often, ecological details are ignored in biogeographical analyses. I use the orchid flora of the Samoan islands to investigate the importance of such details for explaining biogeographical patterns, with special attention to habitat availability and long distance dispersal. Using data on orchid occurrence, island properties, and species traits, I examine putative ecological drivers of species distribution including many that are seldom considered in island biogeography. Simulations show that communities on younger islands are nested subsets of those on older ones. Epiphytic orchids, but not terrestrial orchids, are nested by altitude. Percent endemism is positively correlated with island age in a simple linear regression and positively correlated with altitude in a multiple linear regression that also included distance from the nearest island. ANOVA shows that orchids with high minimum elevations tend to be restricted to one or two islands, whereas widespread orchids tend to have low elevation requirements. These findings suggest that species traits, abiotic environment, cladogenesis, and/or repeated long-distance dispersal affect species distributions. More specifically, altitudinal habitat availability strongly affects orchid occurrence on any given Samoan island. Future contributions to this field should incorporate ecological parameters and identify relevant areas in which further empirical work is needed.
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