The integration of alien plants in plant-hummingbird pollination networks across 8 the Americas : the importance of species traits and insularity

56 Aim To investigate the role of alien plants in mutualistic plant-hummingbird networks, 57 assessing the importance of species traits, floral abundances and insularity on alien plant 58 integration. 59 Location Mainland and insular Americas. 60 Methods We used species-level network indices to assess the role of alien plants in 21 61 quantitative plant-hummingbird networks where alien plants occur. We then evaluated 62 whether plant traits, including previous adaptations to bird-pollination, and insularity 63 predict these network indices. Additionally, for a subset of networks for which floral 64 abundance data was available, we tested whether this relate to network indices. Finally, 65 we tested the association between hummingbird traits and the probability of interaction 66 with alien plants across the networks. 67 Results Within the 21 networks, we identified 32 alien plant species and 352 native 68 plant species. On average, alien plant species attracted more hummingbird species (i.e. 69 aliens had a higher degree) and had a higher proportion of interactions across their 70 hummingbird visitors than native plants (i.e. aliens had a higher species strength). At 71 the same time, an average alien plant was visited more exclusively by certain 72 hummingbird species (i.e. had a higher level of complementary specialization). Large 73 alien plants and those occurring on islands distributed more evenly their interactions, 74 thereby acting as connectors. Other evaluated plant traits and floral abundance were 75 unimportant predictors of species-level indices. Short-billed hummingbirds had higher 76 probability of including alien plants in their interactions than long-billed species. 77 Main conclusions Alien plants appear strongly integrated once incorporated into plant78 hummingbird networks, and thus may have a large influence on network dynamics. 79 Plant traits and floral abundance were generally poor predictors of how well alien 80 species are integrated. Short-billed hummingbirds, often characterized as functionally 81 generalized pollinators, facilitate the integration of alien plants. Our results show that 82 plant-hummingbird networks are open for invasion. 83