Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)



Committee Chair(s)

James A. MacMahon


James A. MacMahon


Plant-pollinator interactions were studied in two subalpine meadows to determine the role of pollination in structuring the herbaceous flower communities. The majority of the entomophilous plant species set significantly less seed when caged to prevent visitation than when exposed to flower visitors. Visitation rate was directly related to temperature and radiation. The number of animal species visiting flowers each week was directly related to the number of plant species in bloom. Most visitor species used ≤3 species of plants, while most plant species hosted ≤8 species of flower visitors. Floral niche breadth increased with increasing animal species diversity, but animal niche breadth was not related to flowering plant species diversity. The mean weekly visitation rate for each plant species was significantly related to floral relative density. Percent seed set was not related to visitation rate or flower density. Flowering period overlap and pollinator similarity varied for most species from one year to the next. There was no indication of competition for pollinators in either community. Supplementing the nectar of Geranium viscosissimum F.&M. resulted in a significant increase in the visitation rate and in the number of visiting species but did not affect either aspect of visitation to the other species in flower. The introduction of Penstemon cyananthus Hook. did not alter the visitation patterns of the other plant species.

Plant-pollinator interactions play an indirect role in the structuring of these floral communities. Cross pollination facilitates high genetic variability in subalpine plants, but does not appear to regulate the plant populations directly.



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