EFFECTS OF PLANT SIZE, PLANT-DENSITY AND SEX DIFFERENTIAL NECTAR REWARD ON POLLINATOR VISITATION IN THE PROTANDROUS ECHIUM-VULGARE (BORAGINACEAE)

The number of bumblebee Bombus spp. approaches to viper's bugloss increased with the number of flowers per plant. The proportion of the number of flowers visited after an approach was smaller in plants with many flowers. Individual flowers on large plants received significantly fewer visits than flowers on small plants. Compared with plants in dense parts of a population, isolated plants received fewer approaches that lasted longer. Number of visits to individual flowers thus did not differ between plants in dense parts of a population and isolated plants. The protandrous flowers lasted for 2-3 days. During the male phase the flowers presented a higher nectar reward and were more frequently visited than during the female phase. -Authors