Flower sex ratio, pollinator abundance, and the seasonal pollination dynamics of a protandrous plant

AIZEN, M.A.

ECOLOGY

ECOLOGICAL SOC AMER

Año: 2001 vol. 82 p. 127 - 144

0012-9658

The separation between staminate and pistillate phases in protandrous, long-lived hermaphroditic flowers results in a seasonal shift in sex ratio from a pure male to a pure female flower population. In theory, temporal sex ratio associated with dichogamy may affect pollination, promoting the evolution of sexual specialization in plants when pollinator visitation does not limit seed output. Alstroemeria aurea, a perennial herb native to the temperate forests of southern South America, bears strongly protandrous flowers. Over a three-year period, I assessed the influence of seasonal changes in flower sex ratio and pollinator abundance on the pollination dynamics of this plant species. Workers of Bombus dahlbomii accounted for >90% of all visits to A. aurea flowers and were the most efficient pollinators on a per-visit basis. As the season progressed, pollen loads carried by bumble bees decreased by almost one order of magnitude, and the amount of pollen deposited per visit decreased as well from >40 to