Regulation of Seed‐Set in Polemonium viscosum: Floral Scents, Pollination, and Resources

Abstract

The effects of pollination and resource levels on seed—set in Polemonium viscosum were evaluated at three elevations: 3528, 3640, and 4025 m in the Rocky Mountains of Colorado. Resource levels were enhanced by weeding out heterospecific neighbors of the plants studied. Flowers are either sweet— or skunk—scented, and the morphs are ecotypically adapted to differences in resource and pollination availability. At the low site, where bumble bees are uncommon and flies common, sweet flowers set fewer seeds than skunky ones; at the highest elevation were bumble bees are common and flies uncommon, sweet flowers set more seeds than skunky ones. Hand pollination increased seedset, indicating that seed—set was pollen limited at all sites. The effects of weeding on seed—set were less consistent than those of hand pollination. Nonetheless, weeding enhanced seed production in sweet—scented flower at the low elevation, and in concert with pollen supplementation also enhanced seed—set in skunky—scented flower at the medium elevation. This pattern is consistent with the hypothesis of ecotypical differentiation between the floral morphs.