Integration of an invasive plant in hummingbird and flower mite networks is driven by ecological fitting and generalization

Abstract

Most plant communities worldwide include exotic plants, which did not evolve with local organisms. The central goal of this study is to test if native organisms expanding to novel hosts are usually generalists or specialists. Here we studied new association between hummingbirds, flower mites and Musa velutina (Musaceae), an exotic plant native to Asia currently invading lowland forests in Costa Rica. Hummingbirds are pollinators, but flower mites feed on nectar without contributing to pollen transfer. Flower mites hitch rides on hummingbird beaks to colonize new flowers. To determine the original diet breadth of hummingbird and flower mite species, we assembled interaction networks including 33 native host plants, 14 hummingbird and 19 flower mite species. Transportation analyses show that flower mites colonization of native or exotic hosts is not constrained by hummingbird flight connections. We identified four hummingbird species visiting Musa velutina. DNA barcodes analyses identified only one species of flower mite colonizing flowers of M. velutina. All new associations with M. velutina involved generalist hummingbird and flower mite species. Musa velutina displays both male and female flowers. Although flowers of both sexes were equally visited by hummingbirds, mites were 15 times more abundant in male than in female flowers. This might be the result of constant immigration coupled with population growth. Only half of the mites hitching rides on hummingbird beaks emigrate to newly open flowers. Our results show that M. velutina integration to a plant community occurs mainly by establishing interactions with generalists.