UBC Theses and Dissertations
Pollen transfer : processes and consequences Lertzman, Kenneth P.
The central theme of this thesis is the processes and patterns of pollen dispersal by. hummingbirds. The main questions are: "To how many flowers past its source is pollen deposited?", and "What are the processes that influence the transfer and and deposition of pollen?". Using powdered dyes as pollen mimics, I conducted laboratory experiments with rufous hummingbirds (Selasphorus rufus) and Indian paintbrush (Castilleja miniata) which showed that dye (and presumably pollen) is carried to many flowers past its source flower. The pattern of pollen deposition was complex and was related to variation in floral morphology. I hypothesized that variation in floral morphology has a strong influence on patterns of pollen transfer. The laboratory experiments also supported the hypothesis that pollen is deposited in partially overlapping layers on the pollinator. A series of models showed that different sets of assumptions about pollen transfer could produce qualitatively similar patterns of pollen deposition, and that variability in deposition increased with the structural complexity of the model. In the model based on the laboratory experiments, variation in floral morphology (defined in terms of the locations where stigmas and anthers contact the pollen pool on the pollinator) had a significant influence on both pollen pool structure (layering) and on pollen carryover. In field experiments on optimal outcrossing and pollen dispersal in Castilleja miniata, I found only very tentative support for a within population optimal outcrossing distance. Variation between years was great: one year's experiment showed a peak of seed production at intermediate outcrossing distances, the other years data showed almost no effect of outcrossing distance. Pollen dispersal (as indicated by dye dispersal) is probably not limited by hummingbird territorial boundaries in this system, in the distance or direction of its movement. I discuss the gap between knowledge of processes at the level of individual flowers and patterns at the level of populations of flowers, and suggest some experiments oriented towards trying to bridge that gap.
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