Prevalence of bird pollination in the Galapagos Archipelago

Abstract

Vertebrate pollination is a frequent phenomenon on islands, resulting from an >interaction release> owing to a density-compensation phenomenon and to arthropod scarcity. Such interaction release and its ecological relevance, however, have never been evaluated at community level. Here we studied for the first time the birdflower interactions in the 12 largest islands of the Galápagos archipelago, combining direct observations on flowers with indirect evidence (pollen transported on birds' beaks and perimandibular feathers). We found 19 bird species (out of the 23 land birds in Galápagos) visiting the flowers of 106 species. A large fraction of these interactions are unique (endemic) to one or a few islands, partly reflecting the different species composition and constraints of each island. Strikingly, one third of the visited flowers are alien, including two of the most invasive plants which are visited by most birds. Birds visit flowers consistently throughout the year and across the islands' main habitats. Our findings highlight the importance of flowers as a prevalent food resource for Galápagos birds at the same time that unravel an underappreciated role of such birds as likely pollinators of a wide array of plant species. The high level of invasions in Galápagos threatens the uniqueness of each island and thus the very essence that makes this archipelago so fascinating. We also advocate that vertebrate pollination in general, and bird pollination in particular, is probably more widespread than previously thought, especially in oceanic archipelagos, though the understanding of this component of biodiversity is still in its infancy.