A Geographic Mosaic of Plant–Pollinator Interactions in the Eastern Caribbean Islands

The interplay between generalized and specialized plant–animal interactions is a core concept in understanding the evolution of mutualisms. Within theEasternCaribbean,Heliconia bihaiis a dominant forest species in the southern island ofSt.Vincent whereH. caribaeais virtually absent.Heliconia caribaeais most common on the northern island ofSt.Kitts whereH. bihaiis restricted to the tops of the highest peaks. Both species are abundant on the central island ofDominica. We compared flowering patterns, nectar characteristics, and visitation frequency of hummingbirds in the two heliconias on the three islands to determine the extent of geographic variations in this plant–pollinator mutualism. The peak flowering season of the two heliconias was observed to be inApril–May on all three islands with little within‐ and between‐island variations. Nectar production significantly varied between species and between islands. Visitation patterns by the principal hummingbird pollinators also varied between the islands: (1) onDominica, only females of a single species of hummingbird pollinated the flowers ofH. bihai(sexual specialization), whereas both sexes of the same hummingbird pollinated the flowers ofH. caribaea(species specialization); (2) onSt.Vincent, both sexes of the same hummingbird pollinated the flowers ofH. bihai(species specialization); and (3) onSt.Kitts, only females pollinated the flowers ofH. bihai(sexual specialization), whereas several species of hummingbird visited the flowers ofH. caribaea(species generalization). We propose that theHeliconia–hummingbird interactions in theEasternCaribbean represent a geographically variable coevolutionary mosaic of plant–pollinator interactions.