AOBPreview originally published online on June 21, 2006
Annals of Botany 2006 98(2):317-334; doi:10.1093/aob/mcl117
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Threatened Pollination Systems in Native Flora of the Ogasawara (Bonin) Islands
Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki 305-0903, Japan
* For correspondence. E-mail tetsuabe{at}ffpri.affrc.go.jp
Received: 25 October 2005 Returned for revision: 6 February 2006 Accepted: 30 March 2006 Published electronically: 21 June 2006
• Background and Aims Various alien species have been introduced to the Ogasawara Islands (Japan). A survey was made investigating whether the native pollination systems fit an ‘island syndrome’ (biasing the flora to dioecy, with subdued, inconspicuous flowers) and whether alien species have disrupted the native pollination network.
• Methods Flower visitors and floral traits were determined in the field (12 islands) and from the literature. Associations among floral traits such as sexual expression, flower colour and flower shape were tested.
• Key Results Among the 269 native flowering plants, 74·7 % are hermaphroditic, 13·0 % are dioecious and 7·1 % are monoecious. Classification by flower colour revealed that 36·0 % were white, 21·6 % green and 13·8 % yellow. Woody species (trees and shrubs) comprised 36·5 % of the flora and were associated with dioecy and white flowers. Solitary, endemic small bees were the dominant flower visitors and visited 66·7 % of the observed species on satellite islands where the native pollination networks are preserved. In contrast to the situation on the satellite islands, introduced honeybees were the most dominant pollinator (visiting 60·1 % of observed species) on the two main islands, Chichi-jima and Haha-jima, and had spread to satellite islands near Chichi-jima Island.
• Conclusions The island syndrome for pollination systems in the Ogasawara Islands was evident in a high percentage of dioecious species, the subdued colour of the native flora and solitary flower visitors on satellite islands. The shape and colour adaptations of several flowers suggested native pollination niches for long-proboscis moths and carpenter bees. However, the domination and expansion of introduced honeybees have the potential for disruption of the native pollination network in the two main, and several satellite, islands of the Ogasawara Islands.
Key words: Dioecy, flower traits, introduced honeybees, island syndrome, oceanic island, pollination niche