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Ogasawara, Japan

Abe T.,Japan Forestry and Forest Products Research Institute | Wada K.,Institute of Boninology | Kato Y.,Tokyo Metroplitan University | Makino S.,Japan Forestry and Forest Products Research Institute | Okochi I.,Japan Forestry and Forest Products Research Institute
Biological Invasions | Year: 2011

The alien predatory lizard, Anolis carolinensis, has reduced the insect fauna on the two main islands of the Ogasawara archipelago in Japan. As a result of this disturbance, introduced honeybees are now the dominant visitors to flowers instead of endemic bees on these islands. On the other hand, satellite islands not invaded by alien anoles have retained the native flower visitors. The effects of pollinator change on plant reproduction were surveyed on these contrasting island groups. The total visitation rates and the number of interacting visitor groups on main islands were 63% and 30% lower than that on satellite islands, respectively. On the main islands, the honeybees preferred to visit alien flowers, whereas the dominant endemic bees on satellite islands tended to visit native flowers more frequently than alien flowers. These results suggest that alien anoles destroy the endemic pollination system and caused shift to alien mutualism. On the main islands, the natural fruit set of alien plants was significantly higher than that of native plants. In addition, the natural fruit set was positively correlated with the visitation rate of honeybees. Pollen limitation was observed in 53.3% of endemic species but only 16.7% of alienspecies. These data suggest that reproduction of alien plants was facilitated by the floral preference of introduced honeybees. © 2010 Springer Science+Business Media B.V. Source

Sasaki T.,Institute of Boninology | Satake K.,Japan National Institute of Environmental Studies | Tsuchiya K.,Tokyo University of Marine Science and Technology
Japanese Journal of Limnology | Year: 2010

Stenomelania boninensis is a thiarid snail endemic to the Ogasawara (Bonin) Islands. Although an alien thiarid snail, Melanoides tuberculata, which presumably has a potential to replace native snails, was recorded from Chichijima in 2005, nothing is known concerning the relationships between these two species. Field surveys on the geographical distribution of the both species were conducted in 39 stream systems on eight islands of the Ogasawara Islands, including Mukojima, Chichijima and Hahajima. As a result, whereas S. boninensis was collected from 33 streams of five islands, M. tuberculata was collected from only five streams in Chichijima. In addition, whereas while S. boninensis was found at both natural and concrete bank sites in freshwater zones, M. tuberculata was found observed at concrete bank sites in both freshwater and tidal zones. The effects of a stream bank construction on both M. tuberculata and S. boninensis were also assessed. Quantitative samplings of the snails were conducted at six stations along the Yatsuse River in Chichijima during a period from immediately before to nine months after the construction was completed. Before the construction, S. boninensis and M. tuberculata coexisted in the reaches of the construction site. During the construction period, both snail species were eliminated by the diversion of all water from the stream. Whereas M. tuberculata recovered at the construction site three months after the construction, S. boninensis failed to recover even after nine months. Moreover, M. tuberculata expanded its distribution range to the upper reaches after the construction. In conclusion, a disturbance like a stream bank construction possibly induces the replacement of native species by aliens. Source

Ando H.,Kyoto University | Setsuko S.,Japan Forestry and Forest Products Research Institute | Horikoshi K.,Institute of Boninology | Suzuki H.,Institute of Boninology | And 3 more authors.
Ecology and Evolution | Year: 2013

Oceanic island ecosystems are vulnerable to the introduction of alien species, and they provide a habitat for many endangered species. Knowing the diet of an endangered animal is important for appropriate nature restoration efforts on oceanic islands because introduced species may be a major component of the diets of some endangered species. DNA barcoding techniques together with next-generation sequencing may provide more detailed information on animal diets than other traditional methods. We performed a diet analysis using 48 fecal samples from the critically endangered red-headed wood pigeon that is endemic to the Ogasawara Islands based on chloroplast trnL P6 loop sequences. The frequency of each detected plant taxa was compared with a microhistological analysis of the same sample set. The DNA barcoding approach detected a much larger number of plants than the microhistological analysis. Plants that were difficult to identify by microhistological analysis after being digested in the pigeon stomachs were frequently identified only by DNA barcoding. The results of the barcoding analysis indicated the frequent consumption of introduced species, in addition to several native species, by the red-headed wood pigeon. The rapid eradication of specific introduced species may reduce the food resources available to this endangered bird; thus, balancing eradication efforts with the restoration of native food plants should be considered. Although some technical problems still exist, the trnL approach to next-generation sequencing may contribute to a better understanding of oceanic island ecosystems and their conservation. © 2013 The Authors. Source

Kawakami K.,Japan Forestry and Forest Products Research Institute | Eda M.,Tottori University | Eda M.,Hokkaido University | Horikoshi K.,Institute of Boninology | And 3 more authors.
Condor | Year: 2012

Bryan's Shearwater (Puffinus bryani) was described in 2011 on the basis of a specimen collected on the Midway Atoll in 1963. This specimen and another recorded on Midway in the early 1990s are the sole reliable rec ords to date. Since 1997, we have found six specimens of a remarkably small Puffinus shearwater morphologically similar to Bryan's Shearwater on the Bonin Islands, northwestern Pacific. In this study, we examined the Bonin samples genetically and confirm that they are of Bryan's Shearwater. A morphological analysis suggests that the small body size and relatively long tail are characteristics of this species. Because the most rec ent individual was found on an islet to the north of Chichijima Island in 2011, the species has evidently survived in the Bonin Islands, where it may breed, although the exact location remains unclear. Three of the individuals found on an islet off Chichijima Island were carcasses preyed upon by black rats (Rattus rattus). Attempts were made to eradicate rats from this island in 2008, and rats may pose a problem on other islands where the shearwaters may breed. Regardless, Bryan's Shearwater appears to be very rare and threatened on the Bonin Islands. To conserve this species effectively, its breeding sites must be identified and the infesting rats eradicated. © The Cooper Ornithological Society 2012. Source

Ando H.,Japan National Institute of Environmental Studies | Setsuko S.,Japan Forestry and Forest Products Research Institute | Horikoshi K.,Institute of Boninology | Suzuki H.,Institute of Boninology | And 5 more authors.
Ibis | Year: 2016

We studied the feeding ecology of the critically endangered Red-headed Wood Pigeon Columba janthina nitens, a subspecies endemic to a very remote and highly disturbed oceanic island chain, the Ogasawara Islands. An analysis based on high-throughput sequencing (HTS) was undertaken on 627 faecal samples collected over 2 years from two island habitats, and food availability and the nutrient composition of the major fruits were also estimated. The HTS diet analysis detected 122 food plant taxa and showed clear seasonal and inter-island variation in the diet of the Pigeons. The results indicated a preference for lipid-rich fruits, but the diet changed according to the availability of food resources, perhaps reflecting the foraging strategy of the Pigeons in isolated island habitats with poor food resources. Pigeons also frequently consumed introduced plants at certain times of year, perhaps compensating for the lack of preferred native food resources. However, the degree of dependence on introduced plants appeared to differ between the two island habitats, so the different impacts of introduced plant eradication on the foraging conditions for the Pigeons on each island should be considered. HTS diet analysis combined with field data may be useful for monitoring the foraging conditions of endangered species and may also inform an appropriate conservation strategy in oceanic island ecosystems with complicated food webs that include both native and introduced species. © 2016 British Ornithologists' Union. Source

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