A PROBABILISTIC ANALYSIS OF POLLINATOR BEHAVIOR AND SEED PRODUCTION IN LOBELIA-DECKENII

Pollination of lobelia deckenii, an African giant rosette lobelia, res ults from foraging by the Mountain Chat (Cercomela sordida) and the Sc arlet-tufted Malachite Sunbird (Nectarinia johnstoni). I measured thre e components of bird behavior leading to fertilization and seed set: ( 1) the arrival rate of birds at focal inflorescences, (2) the number o f probes for nectar made during a visit, and (3) the number of seeds s et per probe. Predicted frequency distributions of seed set per flower , derived by compounding distributions for the three components, match some qualitative and quantitative features of actual seed set pattern s. Stochastic variation in all three components, along with the modula r packaging of ovules in individual flowers, results in high variance among flowers in their contribution to whole-plant female reproductive success, with most flowers receiving inadequate fertilizations for fu ll seed set. The analysis points to the importance of viewing female r eproductive success in plants as a composite entity. Although most flo wers of Lobelia deckenii would set more seeds if additional pollen wer e acquired, sufficient control of pollinator behavior to achieve full fertilization in all fruits may not be possible. The inherent stochast ic variation in fitness contributions among individual flowers may hav e a large influence on the evolution of reproductive traits, including packaging strategies and inflorescence morphologies.