The role of insularity: Plants have few ornithophilous traits but are visited by morphologically more distinct hummingbirds in the Caribbean islands

Functional traits determine interactions between plants and pollinators, and to increase pollination efficiency, many plants have evolved traits to attract specific pollinator groups. However, biogeographical setting may influence trait evolution and biotic interactions. For instance, plants pollinated by hummingbirds often have ornithophilous traits, that is, flowers with elongated corollas, dilute nectar and red colours, but—due to colonization history, depauperate biotas and unstable environmental conditions—it might be disadvantageous for species to rely on mutualistic partners with specific functional traits on oceanic islands. Hummingbird-visited plants on islands are thus expected to have fewer ornithophilous traits and be functionally less diverse in their interactions with hummingbirds. We compiled an extensive dataset of plant—hummingbird interactions (1030 plant and 181 hummingbird species) and associated functional traits. We divided the data into four biogeographical regions across the American mainland and the Caribbean islands and then tested whether biogeographical regions differed in the proportion of ornithophilous floral traits and functional diversity of plant—hummingbird interactions. We found that hummingbird-visited plant communities of the Caribbean islands displayed the lowest proportion of traits typically associated with a functional adaptation towards bird-mediated pollination, with on average the shortest corollas, the highest nectar concentrations and the largest proportion of non-ornithophilous colours. Contrary to our expectations, plants in the Caribbean interacted with hummingbirds that were morphologically more distinct than the plants of mainland regions. Overall, we document a strong imprint of insularity on floral traits and interactions with hummingbirds. While hummingbird-visited plants in the Caribbean displayed floral traits that support island theory, predicting less specific pollination systems on oceanic islands, the functional diversity of plant–hummingbird interactions in the Caribbean communities was higher than on the mainland, possibly driven by competition over resources. These results highlight the influence of insularity on functional traits and plant–pollinator interactions. Read the free Plain Language Summary for this article on the Journal blog.