ISLAND AND MAINLAND POLLINATION ECOLOGY OF CENTROSEMA VIRGINIANUM AND OPUNTIA STRICTA.

(1) In 1981 and 1982 male and female reproductive success of mainland and near- and distant-island populations of Centrosema virginianum and Opuntia stricta growing on two island and one mainland beach communities on the western coast of Florida were compared. (2) Pollen dispersal to neighbouring plants (which was used as an estimate of male reproductive success) was significantly reduced in both island populations of Centrosema relative to the mainland population. Pollen dispersal of Opuntia was significantly lower at the far island than at the near island. (3) Female reproductive success (estimated by fruit set) was significantly lower in Centrosema on the distant island than on the near island or mainland during 1981. Fruit set in Opuntia did not differ between the near and far island however, seeds per fruit were significantly lower on the far island both years. (4) Field experiments indicated significant pollinator limitation of fruit set for Centrosema growing on the far island in 1981, but not in 1982. On the far island in 1983, there was no significant difference in the number of seeds per fruit in naturally-pollinated and hand-crossed Opuntia flowers. (5) The differences between island and mainland pollinator communities and reproductive success that were found in plant communities separated by less than 10 km of water, suggest that pollinator limitation may be an important selective force on plant communities of distant, oceanic islands. [ABSTRACT FROM AUTHOR]