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© The Authors 2015. Oceanic archipelagos are threatened by the introduction of alien species which can severely disrupt the structure, function and stability of native communities. Here we investigated the pollination interactions in the two most disturbed Galápagos Islands, comparing the three main habitats and the two seasons, and assessing the impacts of alien plant invasions on network structure.We found that the pollination network structure was rather consistent between the two islands, but differed across habitats and seasons. Overall, the arid zone had the largest networks and highest species generalization levels whereas either the transition between habitats or the humid habitat showed lower values. Our data suggest that alien plants integrate easily into the communities, but with low impact on overall network structure, except for an increase in network selectiveness. The humid zone showed the highest nestedness and the lowest modularity, which might be explained by the low species diversity and the higher incidence of alien plants in this habitat. Both pollinators and plants were alsomore generalized in the hot season, when networks showed to bemore nested. Alien species (both plants and pollinators) represented a high fraction (~56 %) of the total number of interactions in the networks. It is thus likely that, in spite of the overall weak effect we found of alien plant invasion on pollination network structure, these introduced species influence the reproductive success of native ones, and by doing so, they affect the functioning of the community. This certainly deserves further investigation. ; This research is part of a larger project funded by BBVA Foundation and is also framed within project CGL-2013-44386-P financed by the Spanish Government. R.H. was supported by the Portuguese grant FCT-IF/00441/2013, and by the Marie Curie action FP7-2012-CIG-321794 ; Peer Reviewed

© 2015 Macmillan Publishers Limited. Owing to food scarcity and to the high densities that vertebrates often reach on islands, typical insect-and seed-eaters widen their feeding niche and interact with a greater fraction of species than their mainland counterparts. This phenomenon, coined here 'interaction release', has been previously reported for single species but never for an entire community. During 4 years, we gathered data on bird-flower visitation on 12 Galápagos islands. We show that all sampled land birds exploit floral resources and act as potential pollinators across the entire archipelago, in all major habitats and all year round. Although species and link composition varies among islands, strong interaction release takes place on all islands, making their bird-flower network highly generalized. Interaction release is crucial to the survival of native birds but simultaneously threatens the unique biodiversity of this archipelago, as the birds also visit invading plants, likely facilitating their integration into pristine native communities. ; We thank the BBVA foundation for financing the expeditions and research in Galápagos as well as the Charles Darwin Foundation and Galápagos National Park for logistic support. This manuscript is part of the project CGL2013-44386-P financed by the Ministerio de Hacienda y Competitividad of the Spanish Government ; Peer Reviewed