The Floral Ecology of Sympatric Populations of Amyema pendulum and Amyema quandang (Loranthaceae)

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Abstract
A. pendulum (Sieber ex Spreng.) Van Tiegh and A. quandang (Lindl.) Van Tiegh, are exclusively ornithophilous. The density and diversity of pollen vectors fluctuates during the flowering season of both of these mistletoes. Trilobate pollen grains are dislodged from the anthers while birds forage for nectar and become lodged in, or attached to, the feather barbules of the vector''s forehead, crown or chin. Field observation indicates that birds prefer to forage on A. pendulum when both species are sympatric and co-blooming. The A. pendulum flower has a lower nectar volume and percent of dissolved sugars. It produces more open flowers per branch than its competitor and birds appear to be attracted to the greater floral display over the same period of time. The avian pollen vector species inventory of both Amyema species was virtually the same. Differing floral morphologies, and modes of nectar presentation, between both species appear to be adaptive responses for excluding nectar robbing insects in lieu of encouraging more specialized long billed avian pollinators. The facultatively self-compatible A. quandang produces more viable fruits than the self-incompatible A. pendulum. A comparative study of floral phenologies, floral life-spans and nectar flows suggests that the majority of maturing fruits, in the former species, are the probable result of successful geitonogamy and zoophilous autogamy. A trend towards xenogamy does not appear in A. quandang until the final 3rd of the flowering season when A. pendulum ceases flowering. This is manifested by greater avian patronage and an increase of nectar production in female phase flowers.