The influence of Mimulus ringens floral display size on pollinator visitation patterns

1. Pollinators visiting large floral displays may probe several flowers in sequence, leading to geitonogamous (among-flower) self-pollination. To investigate the relationship between floral display size and patterns of pollinator movement, we studied foraging by several pollinator species in four replicate arrays of Mimulus ringens (Scrophulariaceae). In each array displays were trimmed to two, four, eight and 16 flowers per plant. 2. Bees preferred large displays, and probed more flowers in sequence on large than on small displays. However, the proportion of available flowers probed decreased with display, resulting in nearly equal floral visitation rates across treatments. 3. Because pollinators probed more flowers in sequence on large displays, plants with numerous flowers should experience more geitonogamous self-pollination than plants with small displays. 4. In all four treatments, pollinators frequently visited only one flower before leaving the plant. As the first flower probed on a plant cannot receive geitonogamous pollen, this potentially reduces selfing rates for those flowers, compared to flowers probed late in a long visitation sequence on a plant. Such differences among flowers in pollination history should increase variation in geitonogamous self-pollination among fruits within plants. 5. The three most abundant pollinator species differed significantly in behaviours that could influence plant mating patterns, including number of flowers probed per plant; interplant movement distances; and grooming. Variation in foraging patterns was also evident among individuals within species. These subtle differences in response should affect the pollination services provided to plants.