The integration of alien plants in mutualistic plant–hummingbird networks across the Americas: the importance of species traits and insularity

Abstract

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

Native and alien flower visitors differ in partner fidelity and network integration

“…If the many non‐invasive alien species differ consistently from the native species in for example their interaction patterns it might impose unforeseen consequences in the long run. Using a multi‐species approach, we found that alien flower visitors on the Galápagos tend to be more generalist, hereby corroborating findings from plant focused (Bartomeus et al ; Albrecht et al ; Maruyama et al ) and single pollinator focused studies (Santos et al ). However it stands in contrast to the fairly specialised alien pollinators on Ile aux Aigrettes and Azores (Olesen et al ).…”

“…However it stands in contrast to the fairly specialised alien pollinators on Ile aux Aigrettes and Azores (Olesen et al ). In some network studies pollinators have been found to have a high dependency on alien plants (Bartomeus et al ; Stouffer et al ; Maruyama et al ), and this is here extended to alien flower visitors because the plant species on the Galápagos had a tendency to be more connected to the alien than the native flower visitors (i.e. aliens had higher species strength).…”

The potential indirect effects among plants via shared hummingbird pollinators are structured by phenotypic similarity

“…This finding has an important implication for conservation, as in such systems the introduction of an exotic species that is phenotypically similar to some of the native plants is likely to have a strong impact on native plant‐pollinator networks even if its abundance is low (see also Maruyama et al. ). Overall our results suggest that linkage rules based on plant‐hummingbird trait matching are important factors on plant‐plant indirect pathways.…”

Ecological fitting is a sufficient driver of tight interactions between sunbirds and ornithophilous plants

“…Using this example of a semiarbitrary plant–bird community from three continents, we demonstrated that potential ornithophilous invasive plants can be easily incorporated into local communities. In consequence, we are delivering a similar message from Africa as Maruyama et al () from America. Sunbird pollination networks and hummingbird networks are open to exotic plant species.…”