SYSTEMATIC INCREASE IN POLLEN CARRYOVER AND ITS CONSEQUENCES FOR GEITONOGAMY IN PLANT-POPULATIONS

Thr Fraction of pollen that is carried over from one flower to the nex t as a pollinator visits a sequence of flowers has a strong effect on patterns of mating in plant populations. Although most studies have us ed simple exponential or geometric functions to represent carryover, p ollen deposition patterns often show longer-than-geometric tails, sugg esting a systematic increase in the carryover fraction. We introduce a changing carryover model that allows the carryover fraction to increa se or decrease during a sequence of visits. Maximum Likelihood methods were used to fit constant and changing carryover models to twelve pre viously published data sets. A model with an increasing carryover frac tion provided a better fit than a constant carryover model in 75% of t he cases examined. We found only partial evidence for one proposed cau se of increasing carryover, the burial of donor pollen beneath pollen collected from recipient flowers. Finally, we use the re suits for Ipo mopsis aggregata, a hummingbird-pollinated plant that presents many fl owers simultaneously, to show that the changing carryover model predic ts less pollen will be transferred among flowers on the same plant (ge itonogamy) than does a constant carryover model fit to the same experi mental data.