The effect of bird and bee visitation on pollination and reproductive success in Phormium tenax

Abstract

To study how pollinator composition and abundance influence reproduction of Phormium tenax, we compared pollen deposition by bees and birds to unvisited flowers, and plant reproductive success and outcrossing rates in populations on island and mainland sites that vary in bird abundance. Bees deposited pollen on stigmas if stigmas were close to the anthers but deposited little pollen on stigmas of emasculated flowers, suggesting that they are largely depositing self pollen. Birds deposit pollen on both intact and emasculated flowers with well-exserted stigmas, suggesting they are depositing more outcross pollen. High frequencies of bird claw marks on inflorescences were associated with high fruit set, but not seed set. Seed set and seed outcrossing rates were positively correlated with the number of unique maternal allozyme genotypes in a population and seedlings also showed higher outcrossing rates than seeds, suggesting that genetic diversity, selfing and inbreeding depression limit reproductive success. These results highlight the interplay of pollination and breeding systems in determining plant reproductive success.