When the number of pollen grains deposited on a stigma exceeds ovule numbers, the potential for competition between individual pollen grains exists. In natural plant populations, pollen grain deposition patterns can vary greatly, thus affecting the intensity of pollen competition for ovules. Intensity of pollen competition can in turn affect progeny vigor. We examined pollen deposition patterns, the relationship of pollen deposition to seed set, and the relationship of pollen competition intensity to seedling vigor in a natural population of Clarkia unguiculata. Within 6 hours of receptivity, an average of 61 pollen grains were deposited on stigmas, by 48 hours this number rose to an average of 148 pollen grains. These numbers were sufficient for full seed set in this population which averages 49 seeds/capsule. However, flowers exposed to pollinators for only 6 hours set significantly fewer seeds (23 seeds/capsule) than flowers exposed for 48 hours (35 seeds/capsule), and both treatments set significantly fewer seeds than the average of 49 seeds/capsule for this population. All measures of progeny vigor (percent germination, cotyledon width, and first foliar leaf width) showed no significant differences between the 6 hour and the 48 hour treatments. Our data suggest that the intensity of pollen competition in Clarkia unguiculata affects seed set but does not affect progeny vigor.

Key words: Clarkia unguiculata, competition, deposition, natural population, pollen, progeny vigor