Pollination biology of Hawaiian Scaevola (Goodeniaceae)

Date
2008
Authors
Elmore, Michelle
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Abstract
The genus Scaevola (Goodeniaceae) occurs as shrubs to small trees in diverse habitats in Hawai'i, from coastal strand to montane rainforests. Extensive variation in floral characteristics suggests pollinators differ among species. Bees (Hylaeus spp.) and honeycreepers (Drepanidinae) are the putative native pollinators, but their diversity and abundance have declined over the last century. Due to high rates of extinction among the Hawaiian fauna and the introduction of alien generalists, former roles of some native flower visitors may remain a mystery, and the timeliness of understanding the roles of those still present is underscored. Pol1ination syndromes may offer clues regarding former pollinators that have become extinct or extirpated, or shifted to new resources. This study quantified flower visitation rates, visitor behavior, nectar volume, sugar concentration and sugar composition along with a series of structural measurements of floral display, attraction, and the mechanics of nectar access for all nine extant species of Scaevola in three lineages. Visitation was primarily diurnal, ranging from 0.2 to 3.0 visits• flower-1•hour-1 during the day, with 4-15 visitor taxa per species. Non-native visitors, mainly honey bees (Apis mellifera) and ants, were the most frequent visitors for most species. Hylaeus were infrequent visitors to three species and common only at S. chamissoniana. Birds were the main visitors to S. glabra and S. procera, with the alien Zosterops japonicus a primary visitor to both, and the native Hemignathus kauaiensis also a primary visitor to S. glabra. Visitation was often conducive to pollination for most species. Visitor interactions differed for each species of Scaevola, and in several cases may impose limitations on pollination. There were significant differences in nectar volume, concentration and most floral measurements among and within lineages (P < 0.001). Flowers ranged from small, pale, and scented ones with small amounts of sucrose-dominant nectar in high concentrations to large, heavy, decurved, and brightly colored ones lacking scent and containing copious amounts of dilute, hexose-dominant nectar. Pollination syndromes corresponded with the putative native pollinators. Nearly all Scaevola species exhibit combinations of traits suggesting generalist strategies to allow for visitation by diverse pollinator guilds. Some of these traits may indicate generalist passerine and large moth pollinator guilds that no longer exist among native visitors for some species of Scaevola. The prevalence of alien visitors has several implications for both the plants and native flower visitors. Non-native species may be depriving native visitors of floral resources and may limit plant reproduction if alien visitors are less effective pollinators than native species. Alternatively, non-native visitors may pollinate Scaevola species whose native pollinators have declined or shifted to new resources for unrelated reasons. The research presented herein provides baseline data on flower biology and flower visitation, from which future pollination investigations may be directed.
Description
Thesis (M.S.)--University of Hawaii at Manoa, 2008.
Includes bibliographical references (leaves 86-92).
x, 92 leaves, bound ill. 29 cm
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