The most abundant tree species in much of the undisturbed Hawaiian forests was the subject of a two year study on plant-pollinator interaction 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 collins, 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 compare the pollination ecology of this species and the degree of specialization in the plant-pollinator community with those of similar mainland systems.Endemic Hawaiian birds (Drepanididae) are essential for high levels of fruit set and outbreeding in M. collina. Fruit set was much higher in redflowered 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 predominant flower color in the population, the dimensions of floral parts, and copious nectar secretion adapt this species to bird pollination. However, insects effect moderate amounts of pollination In comparison with mainland communities, the degree of specialization in the plant-pollinator relationship seems to be less in Hawaiian forests, although more information is needed on the Hawaiian lobelias and Sophora chrysophylla before such a statement should be made ~ith any certainty.-i i -
ABSTRACT ••• LIST OF TABLES LIST OF FIGURES INTRODUCTION • •
MATERIALS AND METHODSThe study subjects Nectar measurements -iv-