Anthophilous insect community and plant-pollinator interactions on Amami Islands in the Ryukyu Archipelago, Japan (Original paper)

Abstract

Amami Islands, located in the northern part of the Ryukyu Archipelago, are endowed with subtropical climate and rich flora and fauna containing many endemic taxa. In various types of vegetation on the islands, such as Castanopsis-dominated lowland forests, Symplocos-dominated mountain forests, mangrove forests, coastal scrub and grassland, I surveyed the flowering phenology and anthophilous insect communities of 164 plant species from 1996 to 1999. Flowering was observed throughout the year, and peaked twice in March and July. A total of 2210 individuals of 610 species in 12 orders of Insecta were observed on the flowers. The most abundant order was Diptera (32% of individuals), followed by Coleoptera (28%), Hymenoptera (23%), Hemiptera (11%), Lepidoptera (4%). The bee fauna was composed of six families, 13 genera and 26 species, and characterized by dominance of small bees (e.g., Hylaeus, Lasioglossum and Andrena), large carpenter bees (Xylocopa) and long-tongued anthophorine bees (Tetralonia and Amegilla), and by absence of Bombus. The bee community contrasted with both the honeybee/stingless bee-dominated community in the Asian Tropics and the bumblebee-dominated community at temperate habitats. The rarity of social bees is thought to result from seasonal and annual/supra-annual variability in floral resource on the islands. I inferred the pollinators of each plant species by examining flower-visitor communities, visitor behavior, pollen attachment on visitor's body and floral morphology. Among 104 plant species examined, the most dominant pollination type was melittophily (61%), followed by myiophily (13%), unspecialized entomophily (9.6%), anemophily (6.7%), butterfly

hawkmoth-pollination (6.7%) and cantharophily (2.9%). Among melittophilous species, small-bee-pollinated species (37%) were most dominant, followed by Xylocopa-(21%), Tetralonia-(17%), megachilid-(9.5%), Amegilla-(7.9%) and Colletes/Apis-(6.3%) and wasp-pollinated (1.6%) species. The high proportions of those plants pollinated by long-tongued solitary bees (55.4%) contrasted with the high proportions of bumblebee-pollinated flowers on the mainland of Japan.