title: Evaluating the "recovery level" of endangered species without prior information before alien invasion.
abstract: For maintaining social and financial support for eradication programs of invasive species, quantitative assessment of recovery of native species or ecosystems is important because it provides a measurable parameter of success. However, setting a concrete goal for recovery is often difficult owing to lack of information prior to the introduction of invaders. Here, we present a novel approach to evaluate the achievement level of invasive predator management based on the carrying capacity of endangered species estimated using long-term monitoring data. In Amami-Oshima Island, Japan, where the eradication project of introduced small Indian mongoose is ongoing since 2000, we surveyed the population densities of four endangered species threatened by the mongoose (Amami rabbit, the Otton frog, Amami tip-nosed frog, and Amami Ishikawa's frog) at four time points ranging from 2003 to 2011. We estimated the carrying capacities of these species using the logistic growth model combined with the effects of mongoose predation and environmental heterogeneity. All species showed clear tendencies toward increasing their density in line with decreased mongoose density, and they exhibited density-dependent population growth. The estimated carrying capacities of three endangered species had small confidence intervals enough to measure recovery levels by the mongoose management. The population density of each endangered species has recovered to the level of the carrying capacity at about 20-40% of all sites, whereas no individuals were observed at more than 25% of all sites. We propose that the present approach involving appropriate monitoring data of native organism populations will be widely applicable to various eradication projects and provide unambiguous goals for management of invasive species.
authors.affiliation: Japan Forest Technology Association Rokuban-cho 7, Chiyoda, Tokyo, 102-0085, Japan.
authors.forename: Yuya
authors.initials: Y
authors.lastname: Watari
authors.affiliation: Laboratory of Biodiversity Science, School of Agricultural and Life Sciences, The University of Tokyo 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032, Japan.
authors.forename: Shota
authors.initials: S
authors.lastname: Nishijima
authors.affiliation: Laboratory of Biodiversity Science, School of Agricultural and Life Sciences, The University of Tokyo 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032, Japan.
authors.forename: Marina
authors.initials: M
authors.lastname: Fukasawa
authors.affiliation: Department of Wildlife Biology, Forestry and Forest Products Research Institute Matsunosato 1, Tsukuba, Ibaraki, 305-8687, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Yamada
authors.affiliation: Naha Nature Conservation Office, Ministry of the Environment Okinawa Tsukansha Building 4F, 5-21 Yamashita-cho, Naha, Okinawa, 900-0027, Japan.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Abe
authors.affiliation: Laboratory of Biodiversity Science, School of Agricultural and Life Sciences, The University of Tokyo 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Miyashita
keywords: Carrying capacity; Nansei Islands; invasive species management; long-term monitoring; predation; small Indian mongoose.