抄録
The Bonin White-eye Apalopteron familiare is a threatened endemic species of the Bonin Islands. This white-eye exists on one inhabited island, Hahajima, and its two small satellite islands. Although species used to occur in both the Mukojima and Chichijima island groups, the subspecies there is now extinct. Local extinctions have been attributed to a combination of habitat loss resulting from cultivation and predation by feral cats and introduced rats. The same factors may also be threats to the existing population of white-eyes on Hahajima. Therefore, we estimated the current population size of the white-eye and, using a model simulation we assessed the impacts of: habitat loss, which affects carrying capacity; and predation pressure, which affects breeding success. Population size was estimated taking into consideration variations in population densities among habitat types. The population was estimated to be about 14,700 on Hahajima, and 480 and 420 each on the two satellite islands. A population viability analysis using empirical parameters obtained during field surveys showed almost no extinction risks for any of the three populations under present circumstances. The potential for extinction would drastically increase if the carrying capacity fell to less than 40% of its present status on the small satellite islands. The current findings also indicated that the extinction probability would rise sharply if breeding success dropped to 70% (10 points lower than the current breeding success), on the small islands. The frequency of predation and the population dynamics of the white-eyes must be monitored in order to detect any changes to the species' extinction risk on the islands.
