THE EFFECTS OF FLORAL DISPLAY SIZE ON POLLINATOR SERVICE TO INDIVIDUAL FLOWERS OF MYOSOTIS AND MIMULUS

Large floral displays allow high fecundity but in addition have been postulated to disproportionately attract pollinator visitation, resulting in increased pollination rates to flowers on large plants. Balancing this advantage, however, is the presumed cost of increased self-pollination through transfer of pollen within plants (geitonogamy). Protohystricia huttoni (Tachinidae) responded to larger floral displays in Myosotis colensoi in its native habitat in New Zealand by making more plant-visits per hour, visiting more flowers at each visit, but visiting a declining proportion of the flowers available. As a result, flowers were visited at approximately the same rate (similar to 1 visit per flower per hour) on all display sizes. Pollen deposition, pollen receipt and seed set all varied independently of flower number confirming the even pollinator service to flowers across all plant sizes. Bombus terrestris and Apis mellifera both responded in a very similar way to variation in flower number in naturalised Mimulus guttatus in Britain and, similarly, the proportion of flowers successfully pollinated was independent of flower number. The data presented offer little support for the hypothesis of facilitation of visitation to individual flowers on large displays. Instead, pollinators appear to adopt an ''ideal free distribution'' and utilise floral resources evenly across all plant sizes.