Plant-Pollinator Interactions in Hawaii: Pollination Energetics of Metrosideros Collina (Myrtaceae)

Abstract

The most abundant tree species in much of the undisturbed Hawaiian forest was the subject of a 2—yr study on plant—pollinator interactions and energetics. The purposes of the study were (1) to determine the roles of insects and of some endemic Hawaiian birds in the pollination of the tree Metrosideros collina, (2) to test the hypothesis that maximal outbreeding and seed set occur at intermediate levels of nectar availability, (3) to understand the adaptive significance of profuse flowering in this species, and (4) to determine the degree of specialization in the pollination ecology of this species. Endemic Hawaiian birds (Drepanididae) are essential for high levels of fruit—set and outbreeding in M. collina. Fruit—set was much higher in red—flowered individuals when birds were allowed to use inflorescences than when only insects used them. This is apparently caused by partial self—incompatibility, such that maximal fruit—set occurs only with outbreeding, the primary agents of which are the birds. The pred...