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

Pollination of lobelia deckenii, an African giant rosette lobelia, results from foraging by the Mountain Chat (Cercomela sordida) and the Scarlet-tufted Malachite Sunbird (Nectarinia johnstoni). I measured three components of bird behavior leading to fertilization and seed set: (1) the arrival rate of birds at focal inflorescences, (2) the number of probes for nectar made during a visit, and (3) the number of seeds set 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 patterns. Stochastic variation in all three components, along with the modular 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 full seed set. The analysis points to the importance of viewing female reproductive success in plants as a composite entity. Although most flowers of Lobelia deckenii would set more seeds if additional pollen were acquired, sufficient control of pollinator behavior to achieve full fertilization in all fruits may not be possible. The inherent stochastic variation in fitness contributions among individual flowers may have a large influence on the evolution of reproductive traits, including packaging strategies and inflorescence morphologies.