Ecological and Behavioral Determinants of Pollen Dispersal in Hummingbird- Pollinated Heliconia

Hummingbirds in Costa Rica exploit nectar resources using alternative strategies: some defend a feeding territory while others range widely for their food. In Amazilia spp., both sexes are territorial. In Thalurania furcata, Chalybura urochrysia, and Florisuga mellivora, males are territorial, but not females. In Phaethornis spp., Threnetes ruckeri, and Glaucis hirsuta, both sexes range widely. One of the primary nectar sources for humming-birds in Costa Rica are species of the genus Heliconia (Musaceae). The birds appear to be the primary pollinators of Heliconia. Heliconia species differ in their daily flower output, habitat preferences, and dispersion patterns. Heliconia tortuosa and H. acuminata usually have one flower per inflorescence per day, are forest species, and grow very dispersed in small groups of less than 20 inflorescences. Thus, the nectar they provide is very scattered. Heliconia imbricata, H. latispatha, and H. curtispatha have several flowers per inflorescence per day, are forest-edge species, and grow in large clumps or stands which can number several hundred inflorescences. Consequently, the nectar they provide is concentrated in large quantities in small areas. The dispersed forest species of Heliconia were fed upon by nonterritorial birds, whereas the clumped forest-edge species were fed upon primarily by territorial birds. This interaction may be advantageous to both organisms by lowering the competition for food among birds and the competition for pollinators among the plants. Movement of labeled pollen was extensive in the dispersed populations of forest species and much more restricted in the dense populations of forest-edge species. Possible consequences of these patterns of pollen dispersal for population structure are discussed. Interspecific pollen movement was observed. Heliconia latispatha pollen was found on H. acuminata flowers, and vice-versa. Heliconia imbricata pollen was found on H. latispatha, and putative hybrids of these two species were common in one area.