Mathematical models estimated that xenogamy accounted for 7% and 35% of the stigmatic pollen loads of Ipomoea hederacea and I. purpurea, respectively, in experimental populations. The xenogamy estimate for I. hederacea agreed closely with outcrossing estimates previously reported for this species. The discrepancy between the xenogamy estimate and the previously reported outcrossing estimate for I. purpurea could be explained by differing pollinator flight patterns between experimental and natural populations and/or by selection for cross pollen in the pistil of I. purpurea. Interspecific pollen flow from I. purpurea to emasculated flowers of I. hederacea reduced seed production in the latter. The possible significance of interspecific pollen flow from I. purpurea for the evolution of autogamy in I. hederacea was discussed.
Flowers of Ipomoea purpurea are larger, more colorful, more numerous per plant, and more conspicuous than those of I. hederacea. Because the nectar supply per flower is less variable i: I. purpurea and because the flowers of this species are visually more attractive, Bombus pennsylvanicus demonstrated a foraging preference and greater constancy for I. purpurea than for I. hederacea in experimental and natural sympatric populations in accordance with expectations derived from optimal foraging theory.
Throughout the range of Ipomoea pandurata in North and South Carolina, ants and wasps are attracted to the pedicellar extrafloral nectaries. These hymenopterans are aggressive toward phytophagous insects that visit the plants. Protection of the plant is afforded by these pugnacious hymenopteran nectar feeders.
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