Relative effectiveness of insects versus hummingbirds as pollinators of rubiaceae plants across elevation in Dominica, Caribbean

Most angiosperms rely on animal pollination for reproduction, but the dependence on specific pollinator groups varies greatly between species and localities. Notably, such dependence may be influenced by both floral traits and environmental conditions. Despite its importance, their joint contribution has rarely been studied at the assemblage level. At two elevations on the Caribbean island of Dominica, we measured the floral traits and the relative contributions of insects versus hummingbirds as pollinators of plants in the Rubiaceae family. Pollinator importance was measured as visitation rate (VR) and single visit pollen deposition (SVD), which were combined to assess overall pollinator effectiveness (PE). In the wet and cool Dominican highland, we found that hummingbirds were relatively more frequent and effective pollinators than insects, whereas insects and hummingbirds were equally frequent and effective pollinators at the warmer and less rainy midelevation. Furthermore, floral traits correlated independently of environment with the relative importance of pollinators, hummingbirds being more important in plant species having flowers with long and wide corollas producing higher volumes of dilute nectar. Our findings show that both environmental conditions and floral traits influence whether insects or hummingbirds are the most important pollinators of plants in the Rubiaceae family, highlighting the complexity of plant-pollinator systems214738744FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2015/21457-4The authors thank the Forestry, Wildlife and Parks Division, Dominica, for the research permit to conduct fieldwork in the Morne Trois Pitons National Park. Financial support was provided by Svend G. Fiedler and Wife's Foundation, Oticon Foundation, Torben and Alice Frimodt's Foundation and a PICA Scholarship (LJL). LJL, CR and BD thank the Danish National Research Foundation for support from the Center for Macroecology, Evolution and Climate (grant number DNRF96). PKM was supported by the São Paulo Research Foundation through a Post‐doctoral grant (FAPESP proc. 2015/21457‐4