Insular evolution in plants

    Oceanic islands offer opportunities to study evolution. On oceanic islands, the morphological and ecological evolution of land plants can involve habitat changes (niche expansion), life form (woodiness), sex expression (dioecism), and seed dispersal mode (loss of dispersal abilities). However, a less well-known phenomenon, the loss of extrafloral nectaries on plants has occurred on the Hawaiian Islands, which are isolated oceanic islands. The loss of extrafloral nectaries on plants is thought to be related to the absence of native ants on the Hawaiian Islands.

    Like other oceanic islands, the Ogasawara Islands support many endemic plants (endemism, ca. 70%). We found the similar loss of extrafloral nectaries on a hibiscus endemic to the Ogasawara islands. The ancestral non-endemic species (Hibiscus tiliaceus) produces extrafloral nectar from the sepals, while the endemic species (H. glaber) does not.

Impacts of introduced plants on endemic insects

    Ogasawara Islands support many endemic plants (ca. 70%) and insects (ca. 40%). The insect fauna of the Ogasawara Islands is characterized by forest-dwelling species such as wood-feeding beetles. However, natural forests have been replaced by invasive alien trees (e.g., Bischofia javanica and Casuarina equisetifolia). Because insects and plants are reciprocally dependent, invasive alien trees may affect endemic insects. We investigated the current status of native insect diversity and their associations with alien trees on the Ogasawara Islands.

Bionomics of endemic bees

    Like other oceanic islands, the Ogasawara Islands originally had no social bees. Nine (or ten) solitary bee species occur on the Ogasawara Islands, and all are endemic. Endemic bees are considered important pollinators on the Ogasawara Islands. However, endemic bees other than the large carpenter bee Xylocopa ogasawaraensis have rarely been found on inhabited islands since the 1980s because of the negative impacts of introduced organisms. Consequently, the pollination behavior of endemic bees is poorly understood, and an examination of the roles that endemic bees play in pollinating native plants is needed. We studied the flower visiting behavior of endemic bees.

Invasive alien predators on islands

    Ogasawara Islands support many endemic land snails (endemism, ca. 90%; Dr. S. Chiba's web site). A predatory flatworm, Platydemus manokwari (Global Invasive Species Database), feeds on live snails of any species. The introduction of P. manokwari has been considered a cause of the decline of endemic land snails on tropical oceanic islands. On the Ogasawara Islands, the introduced predatory flatworm has expanded its distribution over a wide area of the largest inhabited island Chichijima, eradicating the land snail fauna. We demonstrated the rapid decrease in land snail survival caused by P. manokwari predation in the field.

     Platydemus manokwari can be readily transported in soil on various materials such as potted plants. Therefore, we proposed a hot water treatment to quarantine such materials.

Publication

Sugiura, S. & Hayashi, M. (2018) Functional compensation by insular scavengers: the relative contributions of vertebrates and invertebrates vary among islands. Ecography, 41: 1173–1183. 

Sugiura, S. (2016) Impacts of introduced species on the biota of an oceanic archipelago: the relative importance of competitive and trophic interactions. Ecological Research, 31: 155–164. (invited review)

Sugiura, S., Tsuru, T. & Yamaura, Y. (2013) Effects of an invasive alien tree on the diversity and temporal dynamics of an insect assemblage in an oceanic island. Biological Invasions, 15(1): 157–169.

Sugiura, S. (2010) Prey preference and gregarious attacks by the invasive flatwormPlatydemus manokwari. Biological Invasions, 12(6): 1499-1507.

Sugiura, S. (2010) Species interactions-area relationships: biological invasions and network structure in relation to island area. Proceedings of the Royal Society B: Biological Sciences, 277: 1807-1815. 

Sugiura, S. (2010) Associations of leaf miners and leaf gallers with island plants of different residency histories. Journal of Biogeography, 37(2):237-244.

Sugiura, S. (2009) Seasonal fluctuation of invasive flatworm predation pressure on land snails: Implications for the range expansion and impacts of invasive species.Biological Conservation, 142(12):3013-3019. 

Sugiura, S. & Yamaura, Y. (2009) Potential impacts of the invasive flatwormPlatydemus manokwari on arboreal snails. Biological Invasions, 11: 737-742.

Sugiura, S., Tsuru, T., Yamaura, Y. & Makihara, H. (2009) Small off-shore islands can serve as important refuges for endemic beetle conservation. Journal of Insect Conservation, 13(4): 377-385.

Sugiura, S., Yamaura, Y., Tsuru, T., Goto, H., Hasegawa, M., Makihara, H. & Makino, S. (2009) Beetle responses to artificial gaps in an oceanic island forest: implications for invasive tree management to conserve endemic species diversity. Biodiversity and Conservation, 18(8): 2101-2118.

Kawazoe, K., Kawakita, A., Sugiura, S. & Kato, M. (2008) Phylogenetic position of the endemic large carpenter bee of the Ogasawara Islands, Xylocopa ogasawarensis(Matsumura, 1912) (Hymenoptera: Apidae), inferred from four genes. Zoological Science, 25(8): 838-842. (cover photo)

Sugiura, S., Yamaura, Y. & Makihara, H. (2008) Biological invasion into the nested assemblage of tree-beetle associations on the oceanic Ogasawara Islands. Biological Invasions, 10(7): 1061-1071. 

Sugiura, S. (2008) Male territorial behaviour of the endemic large carpenter bee,Xylocopa (Koptortosoma) ogasawarensis (Hymenoptera: Apidae), on the oceanic Ogasawara Islands. European Journal of Entomology, 105(1): 153-157. (PDF 252KB)

Sugiura, S., Abe, T., Yamaura, Y. & Makino, S. (2007) Flower-visiting behavior of male bees is triggered by nectar-feeding insects. Naturwissenschaften, 94(8): 703-707.

杉浦真治 (2007)  島の植物に被食防御は必要か？―海洋島での花外蜜腺の消失と移入アリによる影響. 生物科学, 58 (2)：111–114.

Sugiura, S., Abe, T. & Makino, S. (2006) Loss of extrafloral nectary on an oceanic island plant and its consequences for herbivory. American Journal of Botany, 93 (3): 491–495.