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

Abstract

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-

Genetic evidence for recent and incipient speciation in the evolution of Hawaiian Metrosideros (Myrtaceae)

“…Corn (1979) reported that there is extensive outcrossing in Metrosideros because the flowers are protandrous with sticky pollen that is transmitted by native birds that visit the flowers for nectar. Carpenter (1976) observed partial self-incompatibility among red-flowered types and normal seed-set occurs only with outbreeding. The presence of morphologically intermediate forms of these taxa in natural populations may also indicate that these taxa are still connected through significant levels of gene flow.…”

Floral biology and breeding system of pohutukawa (Metrosideros excelsa, Myrtaceae)

“…With its combination of traits that potentially influence outcrossing and selfing, pohutukawa is similar to the mass-flowering Hawaiian Metrosideros collina, flowers of which show a complete overlap of male and female flower functions (Carpenter 1976). Among the Myrtaceae, a diversity of mechanisms have been described that decrease the likelihood of self-pollination (Beardsell et al 1993a).…”

“…Variable expression of self-compatibility within one species has also been reported for several eucalypts, such as E. regnans, E. grandis, and E. cladocalyx, and is presumably a common feature among flowering plants Ellis & Sedgley 1992;Sedgley 1994). Little is known about the breeding system of other Metrosideros species, but Carpenter (1976) reported that redflowered individuals of Metrosideros collina are partially self-incompatible.…”

Interaction between visiting bees (Hymenoptera, Apoidea) and flowers of Ludwigia elegans (Camb.) hara (Onagraceae) during the year in two different areas in São Paulo, Brazil

“…Hara, observed that these plants grew more and accumulated more biomass at higher temperatures than at lower temperatures (22ºC). Carpenter (1976) observed that populations of Metrosideros collina (Forster) (Myrtaceae) growing at different altitudes presented variations in their reproductive stages. Nonetheless, these different populations all showed the same flowering peak.…”