Female and male pollination success of Oncidium ascendens Lindey (Orchidaceae) in two contrasting habitat patches:: forest vs agricultural field

We studied the pollination success of the orchid Oncidium ascendens in two contrasting patches of dry tropical forest; a well-preserved deciduous forest and a tract of continuously disturbed agricultural-pastoral field landscape. O. ascendens is a self-incompatible species whose sexual reproduction depends on cross pollination by the native bee Trigona nigra. We recorded pollinia removal and fruit production during three consecutive years. On average, pollinia removal was three times higher in the well-preserved habitat patch than in the disturbed patch. The rate of pollinia removal increased by about 7% through the 3 years in the forest patch but decreased by 5% in the disturbed site. Fruit production remained relatively constant from year to year in the well-preserved site and decreased in the disturbed patch. On average, fruit production was two times higher in the forest site than in the disturbed patch. Currently O. ascendens is common in both areas, but these results suggest that agricultural activities disrupt pollination and may eventually alter the overall reproductive success and persistence of the orchid population. (C) 2000 Elsevier Science Ltd. All rights reserved.