title: Space, time and aliens: charting the dynamic structure of Galápagos pollination networks.
abstract: 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 also more generalized in the hot season, when networks showed to be more 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.
authors.affiliation: Laboratorio Internacional de Cambio Global (LINC-Global), Institut Mediterrani d'Estudis Avançats (CSIC-UIB), C/Miquel Marqués 21, 07190-Esporles, Mallorca, Balearic Islands, Spain atraveset@imedea.csic-uib.es.
authors.forename: Anna
authors.initials: A
authors.lastname: Traveset
authors.affiliation: Laboratorio Internacional de Cambio Global (LINC-Global), Institut Mediterrani d'Estudis Avançats (CSIC-UIB), C/Miquel Marqués 21, 07190-Esporles, Mallorca, Balearic Islands, Spain Present address: Universidad Internacional SEK, Facultad de Ciencias Ambientales, Calle Alberto Einstein y 5ta transversal, Quito, Ecuador.
authors.forename: Susana
authors.initials: S
authors.lastname: Chamorro
authors.affiliation: Department of Bioscience, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
authors.forename: Jens M
authors.initials: JM
authors.lastname: Olesen
authors.affiliation: Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
authors.forename: Ruben
authors.initials: R
authors.lastname: Heleno
keywords: Alien plants; alien pollinators; biological invasions; global change; mutualistic interactions; oceanic islands