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The role of abiotic mechanisms of long-distance dispersal in the American origin of the Galápagos flora

Abstract:

Aim: Long-distance dispersal research in plants has long been dominated by the assumption that an association between plant diaspore adaptations and related transport vectors (standard dispersal) determines the success of colonization. However, the role of diaspore adaptations in a biogeographic context is being increasingly questioned, as evidence reveals that unspecialized plants have been successful colonizers by recurrent non-standard dispersal. We studied wind and oceanic currents as vectors for long-distance plant dispersal between the Americas and the Galápagos Islands with the focus on diaspore specializations to gain knowledge on the net contribution of standard and non-standard dispersal mechanisms. Location: Eastern Pacific Ocean: the American continent and Galápagos. Major taxa studied: Non-endemic angiosperms native to Galápagos and the American continent. Methods: We used connectivity models for prevailing wind and ocean currents based on satellite data to explore the correspondence between connectivity and species distribution patterns. Using a randomization test to eliminate the effect of wind and current directionality, we evaluated whether the proportion of species that is more connected than randomly expected varies for the five diaspore specialization groups. Results: We found that a large percentage of the plants are present in areas of the continent where ocean current connectivity with the archipelago is higher than expected by chance, while the percentage is small for areas with high wind connectivity. We did not find correspondence between species long-distance dispersal specialization and the connectivity provided by either of the two abiotic vectors. Main conclusions: Our results of ocean current connectivity – over wind connectivity – lead us to hypothesize that rafting dispersal has been significant in connecting the biota of Central/South America and the Galápagos Islands. This result supports a more prominent role of non-standard dispersal mechanisms in a biogeographic context than accepted in traditional schemes.