Nickolas M. Waser, Mary V. Price, Alison K. Brody, and Diane R. Campbell. 2000. Pollination success and plant population size: how strong are the links? Ecological Society of America Annual Meeting, Snowbird, UT.
Abstract. Pollination services to a given plant species are far from constant. For example, 5 yr of observation at 3 permanent sites in the Rocky Mountains separated by 200-400 m indicates a 3-fold range in the rate of visitation to flowers of Ipomopsis aggregata (scarlet gilia), and occasional shifts from hummingbirds to bumblebees as major pollinators. Spatial and temporal variation in pollination does directly translate into seed set in these populations, but density-dependent seedling germination or growth of juveniles might conceivably dampen the signal of variable fecundity before the next generation of adults is reached. To explore this we seeded 6 replicate 8 m2 plots with 750 seeds, and 6 with 1500 seeds, representing average vs. full pollination. A second, single set of plots was seeded with a wider range of 300-3000 seeds. In neither case was there detectable density-dependence in seedling emergence, which averaged ª 6.5% in the 750- and 1500-seed plots and ª 10% in the 300-3000 seed plots. Survival to age 1 yr averaged 39% in 750-seed plots vs. 35% in 1500-seed plots, again not different (P = 0.03). These results do not exclude the possibility of later density-dependence, which our continued censuses of all experimental individuals should detect. This study bears on "pure" issues in plant population dynamics and phenotypic selection analysis, and on strategies for the management of endangered plant populations.