Hyper-specialization for long-billed bird pollination in a guild of South African plants: the Malachite Sunbird pollination syndrome
Date
2009
Authors
Geerts S.
Pauw A.
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A large diversity of floral morphological types exists within the bird pollination syndrome in the Cape Floral Region of South Africa. Here we focus on species with tubular flowers and ask: "Do differences in tube length among plant species correspond to differences in bill length among the birds that serve as pollinators?" To answer this question, we observed 1669 bird-plant interactions at thirteen bird-pollinated plant species across a spectrum of tube lengths. Only three nectar feeding bird species pollinated the focal plant species. The relatively short-billed species were the Southern Double-collared Sunbird (Cinnyris chalybea) and Orange-breasted Sunbird (Anthobaphes violacea); the only long-billed species was the Malachite Sunbird (Nectarinia famosa). We found that the groups of plant species pollinated by the long- and short-billed birds differed significantly in floral tube length. Short-billed sunbirds nevertheless often robbed long-tubed flowers by piercing the corolla, and there was a significant difference in floral tube length among those species that were robbed, and those that were pollinated by short-billed sunbirds. The presence of territorial Malachite Sunbirds depressed robbing rates by short-billed sunbirds at long-tubed flowers. In turn, the absence of Malachite Sunbirds from short-tubed plant species might be explained by the observed positive correlation between tube length and nectar volume. Together, these data suggest that there is a subset of the bird-pollinated plants at the Cape that are pollinated solely by the long-billed Malachite Sunbird, a pollination service irreplaceable by the more abundant, short-billed sunbird species. To extrapolate this finding to a greater subset of species in the Cape Floral Region, we measured flowers on herbarium specimens of all tubular putatively bird-pollinated plants. We find that floral tube length has a bimodal distribution with 37 Cape species potentially dependent on pollination by Malachite Sunbirds. © 2009 SAAB.
Description
Keywords
flower visiting, guild, herbarium, morphology, nectarivory, passerine, plant-pollinator interaction, robbing, specialization, sugar, Africa, South Africa, Southern Africa, Sub-Saharan Africa, Aves, Nectarinia chalybea, Nectarinia famosa
Citation
South African Journal of Botany
75
4
75
4