Experimental studies of pollen carryover: effects of floral variability in Ipomopsis aggregata.

In the montane herb Ipomopsis aggregata, size and placement of stamens and pistils vary substantially among flowers within plants, among nearby plants, and among groups of plants separated by 50-100 m. We trained captive hummingbirds to feed from flowers of this species in a flight cage, and explored the effects of different degrees of floral variability on carryover of fluorescent dyes that act as pollen mimics. We found that the slopes of linear dye carryover functions generally became more shallow as floral variability increased; this led to substantially longer carryover in the treatment with greatest variability. On the other hand, total amounts of dye transferred did not appear to be sensitive to the degree of variability. Floral variability may have a subtle but important effect on plant fitness by influencing the distance of pollen transfer.