The Ecological Impact of Nectar‐Robbing Bees and Pollinating Hummingbirds on a Tropical Shrub

The consequences of nectar robbing by highly social bees were studied at 71 patches of the forest—edge shrub, Pavonia dasypetala (Malvaceae) at two tropical moist forest habitats in central Panama. Groups of Trigona (Trigona) ferricauda (Apidae: Meliponinae) arrived at flowers in early morning; each bee dominated a single flower that it perforated to rob nectar (Fig. 1). Robbers in each patch aggressively defended their feeding sites from the sole pollinator of the plant, the Hermit Hummingbird Phaethornis superciliosus (Trochilidae: Phaethorninae). Less visitation by hummingbirds and reduced seed production resulted from nectar robbing. Flower number in patches was not associated with visitation per flower by pollinators, but patches having the most flowers were entered more often by P. superciliosus. In contrast, thieving P. longuemareus and robbing T. ferricauda showed no patch preference related to total flower number. Seed production per flower was not related to the total number of flowers presented in patches at one time. The average proportion of robbed flowers through the entire flowering episode of P. dasypetala was 36% among 66 patches at one site and 35% among 5 patches at a second site. Reduced seed production was not caused directly by robber damage to flowers, but indirectly through successful deterrence of birds via joint attacks by bees on and near the flower visited by a hummingbird. Further, although fewer seeds were produced by robbed flowers overall, robbed and unrobbed flowers in patches that were heavily robbed did not differ in seed production. Thus robbing primarily influenced reproductive success at the level of the flower patch. P. dasypetala was self—pollinating, yet unrobbed flowers that were not bagged produced 67% more seeds than those not visited by P. superciliosus. Persistent robbing by Trigona may result in selective advantage for autogamous or apomictic P. dasypetala.