[in Japanese]

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One of the potential negative impacts of invasive species is competitive exclusion of native species that have similar or identical ecological niches. Even with extensive knowledge of the similarities between the diets and habitats of invasive and native species, it is difficult to predict the long-term consequences of species interactions over varying spatial and temporal scales with variable resource levels. Here we apply a hierarchical Bayesian model to examine the roles of spatial variations in land use and population densities of the introduced raccoon Procyon lotor and civet Paguma larvata on the population density of the native raccoon dog Nyctereutes procyonoides in the south-eastern Boso Peninsula, central Japan. Our analysis reveals that introduced raccoons negatively affect raccoon dog populations. Substantial numbers of native raccoon dogs and the two invasive mammals have been removed by trapping to control damage to crops. Despite these control measures, the invasive raccoon population has increased, which will likely lead to a reduction in the native raccoon dog population. It is thus imperative to monitor the population trends of native raccoon dogs to conserve this species.

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Deer population management plans formulated by 40 prefectural governments in Japan were reviewed in terms of their current status and issues for refinement. Many management plans proposed control levels of density/abundance and implemented a hierarchical Bayesian model to estimate deer density. However, the validity of the estimated population densities could not be evaluated due to a paucity of prior distributions, model structures, and posterior probability distributions, in addition to a lack of relevant references. Acceptable levels of negative deer impact were proposed qualitatively for agriculture/forestry and ecosystems. However, only two plans proposed quantitative levels to control the impact on the ecosystem. Many plans monitored understory vegetation as an index of the impact of deer on ecosystems, but the monitoring was qualitative in most plans. Furthermore, there was insufficient monitoring of other impacts on ecosystems. To review their management plans, only seven prefectures used scientist discussion groups that were independent of the administrative council. Consequently, the current deer management plans have several flaws, and relevant scientific data must be incorporated to increase their credibility.

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A long-standing interest in ecology is to identify the drivers of wildlife population dynamics because they are important for the implementation of effective management. Recently, increasing numbers of studies have used state-space models for this purpose. However, the collection of sufficient time series data for precise estimation is sometimes difficult; this issue is particularly common in wildlife management. In this paper, we describe a Bayesian model averaging technique that we use in a state-space modelling framework to identify the drivers of wildlife population dynamics from limited data. To exemplify the utility of Bayesian model averaging for wildlife management, we illustrate the population dynamics of wild boars, Sus scrofa, in Chiba Prefecture, central Japan. Two advantages of Bayesian model averaging revealed here are that it can (1) readily evaluate the relative importance of the drivers of population dynamics and (2) improve model predictability while avoiding overfitting problems. Although Bayesian model averaging is not used commonly in a state-space modelling framework, we believe that it helps to develop effective management plans, even from limited time series data.

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Ronald A. Fisher pointed out that Bayes (1763) estimation, which uses flat prior distributions, contains a fatal problem: we can create any estimate we like by changing the transformation used before the analysis. Therefore, Fisher proposed the maximum likelihood estimation (ML estimation) to replace Bayes (1763) estimation. However, the ML estimation procedure is sometimes more difficult than Bayes estimation using the Markov chain Monte Carlo (MCMC) method. In such cases, we should use the adjusted Bayes (1763) estimation to obtain ML estimates; we can use the median of the posterior distribution as the ML estimate if we use an appropriate transformation (empirical Jeffreys prior) that makes the posterior distribution roughly symmetrical. We can find the appropriate transformation by finding the Box-Cox transformation that makes the skew of the posterior distribution nearly zero. In this case, we can use the 2.5% and 97.5% quantiles of the posterior distribution as the Fisherian 95% confidence interval. In this case, the posterior distribution approximates the fiducial distribution that is the probability distribution of parameters. I show an example of the calculation using a dataset for the population of sika deer, Cervus nippon, in Hokkaido, Japan.

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We report the management history of the Asiatic black bear (Ursus thibetanus) in Hyogo Prefecture, including population estimates obtained through monitoring methods that use data provided from damage control measures. To prevent extirpation of the bear population, the first Specified Wildlife Conservation and Management Plan in Hyogo determined that all bears captured as nuisances for the first time and miss-trapped should be released. We recorded the history of released bears using microchips embedded subcutaneously at the time of capture. If a bear was killed as nuisance control, dissection was performed to assess the bear’s age, nutritional condition, and breeding status. Thus, we were able to estimate population size and trends using a model combining mark-recapture and harvest-based methods. We observed an increasing population trend from 2005-2016; the estimated median number of individuals exceeded 800 in 2015 and 2016. Our analysis of the reproduction status of adult females, assessed independently from the population estimation, indicated that more than 95% of adult females exhibited signs of breeding every other year. These data indicate that there is no risk of Asiatic black bear extirpation in Hyogo. Consequently, bear hunting resumed in 2016 after a 20-year ban.

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In regions with heavy snowfall, salt is commonly used to de-ice roads to improve winter traffic safety. However, little is known about the effects of de-icing salt on flora and fauna. Here, we examined the potential effects of CaCl₂ on the survival of two salamander species, Hynobius retardatus and H. lichenatus (Hynobiidae), endemic to Hokkaido and Tohoku, Japan, respectively. In the laboratory, we exposed eggs and larvae of the salamanders to various concentrations of CaCl₂ dissolved in water. We found that the median lethal concentrations (LC50; CaCl₂ equivalent) were 316.6 and 234.4 mg/L for eggs and 271.1 and 519.0 mg/L for larvae of H. retardatus and H. lichenatus, respectively. Additionally, when eggs of H. retardatus were exposed to CaCl₂ concentrations ≥ 400 mg/L, 17.9% of hatchlings had abnormally developed gills. These results suggest that CaCl₂ de-icing salt can have negative effects on the survival of salamander eggs and larvae if its concentrations in natural ponds are higher than the effective levels reported here.

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The baited-trap method is recommended for capturing and eradicating the invasive crayfish, Procambarus clarkii, for biodiversity conservation and ecosystem management. However, few experimental studies have examined the efficiency of the different types of bait trap used for varying durations. Therefore this study compared the capture efficiencies of Kagoami, Anagokago, Kanikago, and Amimondori bait-traps by considering the number of crayfish captured per given period of trap operation. The number of crayfish captured increased with time after the traps were set, reached a maximum, and then decreased. Over the study period, the Kagoami and Anagokago traps had the highest trap yields; however, for short trap operations of less than 5 hours, the Amimondori trap caught as many crayfish as the Kagoami and Anagokago traps. The trap escape rate increased after the bait lost potency, and the number of crayfish that escaped was greater for traps with open entrances versus those with narrow entrances. Overall, the capture efficiencies of the traps peaked at 0.2 days for the Amimondori trap, 1-3 days for the Anagokago trap, and 7 days for the other traps. Considering the trap characteristics, we recommend using a different combination of bait traps, in different orders and for varying durations, to maximise trapping efficiency, i.e., when crayfish are abundant, operate the Amimondori trap for several hours and then shift to the Anagokago trap to ensure long-term trapping of crayfish as the crayfish density decreases.

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We compared point count and sound recording survey results for the conservation and monitoring of birds in the subtropical evergreen broadleaf forests of Amami-Oshima Island, Japan. We conducted surveys at five sites in the morning and at night between April 22 and May 6 (breeding season) in 2015 and obtained similar data on the composition of bird species, including for conservationally important bird species, such as Zoothera dauma major and Garrulus lidthi, using both methods. Recorded Luscinia komadori and Otus elegans song or call frequencies were significantly correlated with abundance as estimated by point counts, suggesting that the sound recording method can be used to estimate the abundance of these species.

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Populations of two unionid mussel species, Pronodularia japanensis and Unio douglasiae nipponensis, have drastically decreased over the past 25 years in Matsuyama Plain, Ehime Prefecture, Japan. A native bitterling, Tanakia lanceolata, depends on these mussels as its spawning beds; thus, the conservation of unionid mussels is necessary to prevent an extinction cascade. In Matsuyama, the bitterling Tanakia limbata has been introduced by humans and its distribution now extends across the entire T. lanceolata habitat, leading to hybridization with T. lanceolata. In this study, we introduced P. japanensis to four sites within two nature restoration ponds (Matsubara Pond and Hirose-gasumi) and one site in a spring-fed pond (Yanahara Pond) and monitored them for 1 year. Our objective was to conserve this unionid and construct a refuge for endangered unionids and bitterlings, from which invasive bitterling species would be removed. We measured the density of the diatoms on which unionids feed, water temperature and depth, dissolved oxygen content, and the size of substrate particles at our study sites. We found that the survival rates of introduced P. japanensis were 37% over a period of 1 year at Hirose, and 75% over 6 months at the downstream Matsubara site. All individuals in the other three sites died within 1 year. These survival rates were affected by diatom density; the two sites with high survival rates were higher in diatom density than the three remaining sites. At Hirose and the downstream Matsubara site, dissolved oxygen content fell to 3-5 mg/L between October and November, 2015. During the monitoring period, we observed introduced mussels emerging from the substrate and exposing their entire shells to the bottom surface. This behaviour was significantly related to the probability of death within 2 weeks, and likely indicated an attempt at escape from an unsuitable environment. In Yanahara Pond, we observed that invading T. limbata spawned on introduced P. japanensis. These results suggest the following necessary conditions for constructing a refuge for P. japanensis and T. lanceolata: 1) a sufficient supply of diatoms, 2) dissolved oxygen content is maintained above 5 mg/L for years, and 3) prevention of invasion by non-native bitterlings. During monitoring, it is necessary to verify that introduced unionids are infaunal under the substrate during winter. In our study sites, the addition of silicate and/or the construction of a flow-retention structure to increase diatom density and remove invasive floating leaf plants (to maintain sufficient dissolved oxygen) will enhance the effectiveness of the downstream Matsubara site and Hirose as refuges.

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The distribution of the endangered piscivorous fish Opsariichthys uncirostris uncirostris (O. u. uncirostris) was investigated along ca. 90 km of the west shoreline of Lake Biwa, central Japan. The species was observed at 135 of the 365 sites. A generalised linear mixed model (GLMM) was used to examine the occurrence of adult and immature fish with the explanatory variables of the lake bottom (sand, gravel, and other), watercourse shape (surface, subterranean, dried-up stream, and shore), presence of reeds, presence of watercourse embankments, presence of trees on the watercourse side, and season, with the site as a random effect. The GLMM indicated a positive effect of sandy and gravel-bottomed environments on the presence of O. u. uncirostris. According to the distribution map of this species, the northern area possesses more sites with sandy or gravel bottoms, which might provide a better habitat. I used PERMANOVA to examine the combinations of presence/absence of adult and immature fish for 332 research sites. The analysis showed that the lake bottom and presence of watercourse embankments variables were significantly associated with the occurrence of O. u. uncirostris. Therefore, to promote use by this species, sandy and gravel-bottomed environments should be protected together with their source, i.e. tributary rivers.

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In the Ogasawara Islands, Japan, the invasion of alien species, such as the green anole and honeybee, has affected the pollination of native plant communities. Although these disturbances are predicted to have negative effects on the genetic diversity and reproductive success of native plant species in the Ogasawara Islands, the effects on genetic characters are still unclear. This study compared the pollinator fauna and reproductive success of Leptopetalum grayi (Rubiaceae) on Chichijima and Mukojima, in the Ogasawara Islands. On Mukojima, many native pollinators have survived because there are no invasive alien species. We also compared the genetic diversity of adult plants and their seeds using 14 microsatellite markers. There were fewer native flower visitors on Chichijima than on Mukojima. The fruit set rate was also significantly lower than on Mukojima (P < 0.05). These findings indicate that the pollination disturbance on Chichijima has had negative effects on reproductive success. Nevertheless, there were no significant differences in the genetic diversity of adult plants or seeds on both islands. This implies that genetic diversity has not yet been affected by the disturbed pollination on Chichijima.

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The 2011 Tohoku earthquake drastically changed human activities in parts of Fukushima Prefecture, Japan. The subsequent tsunami damage and radioactive fallout from the Fukushima Daiichi nuclear power plant resulted in the abandonment of agricultural land and towns, allowing the expansion of wild mammal populations into areas previously inhabited by their domesticated relatives. This study examined possible hybridisation between wild boars and domesticated pigs in Fukushima. We analysed the mitochondrial DNA sequences of 75 wild boars collected from Fukushima populations between 2014 and 2016. While 71 boars had Asian boar haplotypes, four boars identified as wild boars phenotypically had mitochondrial genomes extremely close to that of European domesticated pigs, implying ongoing genetic contamination of wild boar populations from feral domesticated pigs. This suggests the need for detailed genetic monitoring using nuclear DNA markers and population management based on genetic data.

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We report a case of natural vegetation regeneration after a mudslide, under conditions of extremely high deer population density. In 1996, a large mudslide completely removed vegetation and soil in a valley within an evergreen broadleaf forest in Yakushima, Japan, that was densely inhabited by sika deer (Cervus nippon yakushimae; 100–350 individual/km²). We conducted surveys at two plots (28.3 m²) in 2007, 2011, and 2017 in the valley. The number of saplings 5–30 cm and trees ≥150 cm in height, and the total basal area increased in the plots after the mudslide. In 2017, we established three belt transects (width: 2 m; lengths: 16, 28, and 40 m) across the valley, counted trees of each species ≥ 150 cm, and recorded the coverage of each plant species < 150 cm that was exposed to deer feeding pressure. The vegetation consisted of ≥ 11 ferns, 8 herbaceous plants, and 39 woody plants; of these, at least 51 species were food species, including 16 that were palatable to deer. These results suggest that natural vegetation gradually recovers despite very high feeding pressure from deer. Further surveys should identify the vegetation that ultimately establishes in this forest.

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The food habits of two populations of the raccoon dog, Nyctereutes procyonoides, along the Pacific sand-dune coast of northern Japan were studied. These raccoon dog populations recovered after the March 11, 2011 tsunami. One population was in Minami-Gamou, Sendai, where habitat recovered after the tsunami. The other population was in Terashima, Iwanuma, 22 km farther south, where the effects of both the tsunami and restoration were weaker. Unexpectedly, the populations were not dependent on fish, shellfish, crabs, and seaweed, but were dependent on the berries of shrubs like Rosa luciae and Coriaria japonica that grew in the sandy coastal habitat and survived the tsunami, and those of exotic forbs like Phytolacca americana, which invaded the habitat 1~3 years after the tsunami. The greater dependency of the Minami-Gamou population on man-made materials, such as plastic bags, rubber bands, and expanded polystyrene, was probably the result of habitat destruction and large-scale reconstruction activities. Their food habits were similar to those of other raccoon dog populations in Japan, eating more insects in summer, fruit and seeds in autumn, and small mammals in winter. This study suggests the need to consider the healthy food web and network of the costal ecotone for the future conservation and recovery activities.

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To determine directions for future developments in citizen science, we examined differences between the Japaneselanguage concepts of 科学, 研究, and 市民 and the English-language concepts of science, research, and citizen. We found that the English word “research” is important in denoting new findings, whereas the corresponding Japanese word “研究” does not communicate novelty. East Asians, particularly those from Japan, tend to apply the word “citizen” to adults, whereas Europeans and North Americans apply the word to members of all generations, including babies and children. We also examined the applicability of the new concept of “市民科学” (citizen science), as defined by Sasaki et al. (2016), in studies of fish. Based on our findings, the use of “市民科学” (citizen science) is suitable for describing the process of becoming a scientist as well as indirect contributions to science. We also discussed the value of pursuing Japanese originality in science.

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