Nakanoshima Island Research Articles

The long‐term drive count and culling data of the sika deer (Cervus nippon) population introduced on Nakanoshima Island in Lake Toya, Hokkaido, Japan, during 1980–2023

AbstractCervid populations introduced to favorable habitats in confinement often increase excessively without predators and hunting. Overabundant deer populations impact the ecosystems and may cause damages to agriculture and forestry. Long‐term count data on the changes in a deer population is essential to understand the relationship between the population dynamics and the natural vegetation. The introduced sika deer (Cervus nippon Temminck, 1836) population without predators on Nakanoshima Island, Hokkaido, Japan, showed repeated irruptions and declines with mass mortality and irregular culling between 1980s and 2000s. The overabundant deer significantly altered the natural vegetation, and density‐dependent changes in population parameters such as body size and reproduction were observed. Here, we present the drive count and culling data to examine the population dynamics during 1980–2023. Deer were counted by 20–30 walking drivers and 2–3 observers on boats once per year in February or March. The number of counted deer rapidly increased from the original three introduced around 1960 to >270 deer (the first peak) in two decades and decreased by half due to starvation and the first culling. Thereafter, the number of counted deer continued to increase with a lower growth rate, reached a higher peak (>400, the second peak) than the first irruption in two decades, and decreased again by half due to starvation and the second culling. Although the number of counted deer increased again up to >300 in several years, it decreased and was maintained at around 100 deer with the annual culling program since 2012. The complete data set for this abstract published in the Data Article section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2024-06.1/jalter-en.

Amplitude enhancement of short period GPS-TEC oscillations over rainfall area

Correlation between rainfall and short period GPS-TEC (total electron content) variations are investigated by using the precipitation data obtained on the ground and estimated from satellite observations (JAXA/GSMaP) as a proxy of lower atmospheric wave activity. The GPS-TEC data obtained at a tropical station, PHIM, in Phimai, Thailand, for 2014–2020, and the data obtained at a mid-latitude station, NAKG, in Tokara Nakanoshima Island, Japan, for 2017–2019, are examined. A statistical analysis of MEM (maximum entropy method) power spectral density (PSD) in the period range from 50 to 1200 s over PHIM clearly shows an enhancement in the cases of rainfall from that in no-rainfall cases, in particular, on the dusk side. The enhancement is observed both acoustic wave periods less than 5–6 min and internal gravity wave periods more than 10 min. The enhancement after sunset could be an effect of strong rainfall more frequent on the dusk side than that in other local time, or it could suggest the importance of ionospheric electron density profile change for the TEC variation. On the other hand, the PSD does not show such clear enhancement over NAKG on the dusk side, although it shows a small enhancement on both dayside and night-side. A clear PSD bulge near the main vertical acoustic resonance periods, i.e., around 275 s, appears in the average PSD profile of the TEC at PHIM, which suggests that the resonance effect contribute to some extent the PSD enhancement under rainy condition. An event analysis also suggests the contribution of acoustic resonance to the enhancement of the short period TEC variation. A complicated spatial distribution of TEC oscillation over a rainfall area around PHIM, where the TEC oscillations with various periods co-exist, is presented.Graphical

Discovery of the genus Platycotylus Olliff, 1883 (Coleoptera, Tenebrionidae) in Japan: Description of a new and remarkable species.

The genus Platycotylus Olliff, 1883 (Coleoptera: Tenebrionidae) is recorded from Japan (Nakanoshima Island, Tokara Islands) for the first time, through the discovery of a new and remarkable species, Platycotylusmerklisp. nov., which is described herein. The male of this new species can be distinguished from all known males of other congeneric species by its long and asymmetrical epistomal horn. Although this new species is most similar to Platycotylusparvicollis (Pic, 1923), for which a male has not been examined, it can be distinguished from this species by its simple sparse pronotal punctation, smaller eyes, and acutely produced temples.

屋久島，黒島，口之島，中之島に分布するシイ型照葉樹林の種組成および種多様性

屋久島，黒島，口之島，中之島に分布するシイ型照葉樹林の種組成および種多様性

Comparison of Age-at-Death Patterns in the Irruption and Post-Population-Crash Phases of an Introduced Sika Deer (Cervus nippon) Population

Age-specific changes in deer demographic parameters under food limitation are an important factor in predicting the post-population-crash dynamics of irruptive deer populations. To evaluate the differences in age-class-at-death between the initial irruption and post-population-crash phases of a sika deer (Cervus nippon) population, we analyzed a dataset of naturally dead carcasses from an introduced sika deer population on Nakanoshima Island, Japan. We predicted that the occurrence probability of fawn-class sika deer carcasses would increase in the post-population-crash phase and that the occurrence probability of old-class sika deer carcasses (≥ 10 years old) would decrease during this phase. Contrary to our expectations, the relative occurrence probabilities of four age classes [fawn, yearling, prime-aged (2–9 years old), and old] of sika deer carcasses did not differ between the initial irruption and post-population-crash phases. This could partially be a side-effect of classifying deer age into just four categories; slight changes within the age classes could not be detected because of this statistical limitation. Comparative studies are required to determine whether these results coincide with other irruptive deer populations.

Characteristics of soils and plants in Nakanoshima Island of Lake Toya, with a high density of sika deer

Characteristics of soils and plants in Nakanoshima Island of Lake Toya, with a high density of sika deer

Effects of culling intensity on diel and seasonal activity patterns of sika deer (Cervus nippon)

Adaptive hunting management is commonly used for controlling the populations of overabundant large herbivores; however, induced behavioural changes can make the effective control of target populations difficult. However, few studies have compared the impact of different levels of hunting intensities on the activity patterns of ungulates before, during, and after a culling program. We investigated how different culling intensities affect the activity patterns of sika deer on Nakanoshima Island in Lake Toya, Hokkaido, Japan using camera-trap surveys comparing the period of treatment before, during, and after a culling program. We used the number of deer photographed per hour per camera as an index of activity. Sika deer showed consistent crepuscular activity patterns (i.e., dawn and dusk) during spring–summer and trimodal activity patterns (i.e., dawn, dusk, and midnight) in autumn throughout the study period. In response to increased culling intensity, the activity peaks shifted slightly towards the night. The shift towards nocturnal activity persisted during post-culling period. Understanding the changes in activity patterns in response to culling intensity could be used to facilitate population control and assist in establishing a night shooting program. Thus, wildlife managers should consider night shooting once hunting during day time has shifted the normal diurnal activity of deer to nocturnal activity.

Demographic analysis of the irruptive dynamics of an introduced sika deer population

AbstractIrruptions of large herbivores, with a rapid population increase to peak abundance, are widely observed. Occasionally, there is a population crash following such peaks in abundance, after which the population recovers to form another peak typically lower than the initial. There are mathematical models describing this full cycle of irruptive dynamics. The insight for further improvement of such mathematical models will be obtained from demographic analyses of irruptive dynamics incorporating density‐dependent and density‐independent resource limitations. Using a 35‐yr dataset on the irruptive dynamics of an introduced sika deer (Cervus nippon) population on Nakanoshima Island, Japan, we evaluated the factors and stages determining irruptive dynamics (phase 1: the initial irruption and population crash; phase 2: subsequent dynamics) through key‐factor/key‐stage analysis of the population structure, estimated using age‐at‐death data of naturally dead deer. We set two factors (i.e., deer density and snow accumulation) and three life stages (i.e., immature individuals, adult female, and adult male). The estimated population structure showed two population crashes and a density peak higher than the initial peak during population regrowth subsequent to the initial population crash. The most influential factor and stage for determining the population dynamics differed between phases 1 and 2. The contribution of deer density to the variability in population change was the largest in phase 1 (62.30%) and decreased to 24.10% in phase 2. The contribution of snow accumulation was small in both phase 1 (11.74%) and phase 2 (0.64%). The male stage had the largest contribution in phase 1 (39.23%), while the immature stage had the largest contribution in phase 2 (63.31%). The female stage had the smallest contribution in both phase 1 (24.19%) and phase 2 (17.67%). Population growth rate decreased, while carrying capacity increased, in phase 2 compared to phase 1. We suggest that the small contributions of density‐dependent and density‐independent resource limitations on population dynamics in phase 2 were related to the characteristics of alternative foods (fallen leaves and woody plants) that were newly utilized by deer in phase 2. We conclude that alternative resources potentially generate various irruptive dynamics, including unstable dynamics not expected in the classic paradigm.

Robustness of adult female survival maintains a high-density sika deer (Cervus nippon) population following the initial irruption

Context Irruption of large herbivore populations is characterised by three distinct phases: (1) an exponential increase in population to a peak abundance; (2) a population crash; and (3) a second increase to another population peak, typically lower than the first peak of abundance. However, there has been little study of age- and sex-specific factors that affect the post-initial irruption interactions with food sources. Aims We aimed to investigate annual survival rates of sika deer (Cervus nippon Temminck, 1838) in the sequent irruption of a population on Nakanoshima Island, Lake Toya, Japan, with a chronically high density during the period 2002–12. Methods Survival monitoring data were obtained for 219 individuals (93 males and 126 females) using radio-collars. Annual survival was quantified, and related factors, i.e. deer abundance and winter severity, were determined by model selection using Akaike information criterion values. Key Results The results showed that annual survival rates across sexes and age classes (fawn, yearling, prime-aged, old) decreased with increasing population density, snow depth and winter precipitation. Winter severity had a greater effect on adult survival than density regulation. Nevertheless, female adult survival was maintained at a high level, with a mean of 0.84 (95% CI: 0.80–0.88). Key conclusions Robust survival rates for adult females might contribute to the maintenance of a high-density sika deer population in the post-initial irruption. Implications We suggest that in the absence of predation and hunting, sika deer population is not able to self-regulate to the density level that avoids an irreversible impact on plants.

Effects of an increase in population of sika deer on beetle communities in deciduous forests.

The overabundance of large herbivores is now recognized as a serious ecological problem. However, the resulting ecological consequences remain poorly understood. The ecological effects of an increase in sika deer, Cervus nippon Temminck (Cervidae), on three insect groups of beetles was investigated: ground beetles (Carabidae), carrion beetles (Silphidae), and dung beetles (Scarabaeidae and Geotrupidae) on Nakanoshima Island, Hokkaido, northern Japan. We collected beetles on Nakanoshima Island (experimental site) and lakeshore areas (control site) and compared the species richness, abundance, diversity index, and community composition of beetles between the sites. Results showed that although both species diversity and abundance of carabid beetles were significantly higher at the lakeshore site, those of dung and carrion beetles were higher at the island site. It was additionally observed that abundance of larger carabid beetles was higher at the lakeshore site, whereas that of small-sized carabid beetles did not differ between the lakeshore and island sites. For dung beetles, abundance of smaller species was higher at the island site, whereas that of large species did not differ between the lakeshore and island sites. Abundance of two body sizes (small and large) of carrion beetles were both higher at the island site. Overall, the findings of this study demonstrated that an increase in deer population altered the insect assemblages at an island scale, suggesting further changes in ecosystem functions and services in this region.

Comparison of Drive Counts and Mark-Resight As Methods of Population Size Estimation of Highly Dense Sika Deer (Cervus nippon) Populations

Assessing temporal changes in abundance indices is an important issue in the management of large herbivore populations. The drive counts method has been frequently used as a deer abundance index in mountainous regions. However, despite an inherent risk for observation errors in drive counts, which increase with deer density, evaluations of the utility of drive counts at a high deer density remain scarce. We compared the drive counts and mark-resight (MR) methods in the evaluation of a highly dense sika deer population (MR estimates ranged between 11 and 53 individuals/km2) on Nakanoshima Island, Hokkaido, Japan, between 1999 and 2006. This deer population experienced two large reductions in density; approximately 200 animals in total were taken from the population through a large-scale population removal and a separate winter mass mortality event. Although the drive counts tracked temporal changes in deer abundance on the island, they overestimated the counts for all years in comparison to the MR method. Increased overestimation in drive count estimates after the winter mass mortality event may be due to a double count derived from increased deer movement and recovery of body condition secondary to the mitigation of density-dependent food limitations. Drive counts are unreliable because they are affected by unfavorable factors such as bad weather, and they are cost-prohibitive to repeat, which precludes the calculation of confidence intervals. Therefore, the use of drive counts to infer the deer abundance needs to be reconsidered.

Stenichnus lackneri sp. n. of Japan (Coleoptera, Staphylinidae, Scydmaeninae).

Stenichnus Thomson, 1859 is a species-rich and common genus in the western Palaearctic, but only a few species are known from the Far East. Six species have been so far recorded from Japan (Sharp 1886; Jałoszyński 2004, 2006; Jałoszyński, Arai 2009). Interestingly, the Japanese species occur in the temperate or cool climate of Hokkaido in the north-east (Stenichnus minipollens Jałoszyński, 2004) and in subtropical forests of the south-western Yaeyama Archipelago (St. bellulus Jałoszyński, 2004 and St. totoro Jałoszyński, 2004), showing a broader range of ecological plasticity than their western Palaearctic congeners. Two more species are known to occur in the Japan mainland, i.e., St. pollens (Sharp, 1886) in Kyushu and St. sakurayamanus Jałoszyński & Arai, 2009 in the central part of Honshu, and one species, St. mitai Jałoszyński, 2006, was discovered on the small Nakanoshima Island of the Tokara Archipelago. Only the species that occur in the Yaeyama Islands are relatively common, all remaining species are known from holotypes only. Interestingly, St. pollens and St. minipollens, which occur on different islands separated by nearly 1500 km, share very similar aedeagi with a unique long ventral projection (Jałoszyński 2004).

電磁探査を用いた隠岐島前・中ノ島における塩水・淡水分布に関する検討

電磁探査を用いた隠岐島前・中ノ島における塩水・淡水分布に関する検討

Seasonal Variation of Activity Pattern in Sika Deer (Cervus nippon) as Assessed by Camera Trap Survey

Ungulate populations such as deer and wild boars have been expanding in range and increasing in number throughout many areas of the world. Regulation of these overabundant populations is urgently needed. For an effective culling program addressing these overabundant populations, it is essential to have information on the activity pattern of animals. To determine the factors affecting seasonality of daily activity pattern in sika deer, we studied deer activity through camera traps on Nakanoshima Island, Lake Toya in Hokkaido, Japan, where human disturbance is low. We estimated activity pattern during four time periods (dawn, dusk, day, and night), and evaluated the effects of weather conditions on activity pattern (camera trap rate) for each period. Deer activity at dawn, dusk and night showed clear seasonal patterns, with peaks in September, while the activity pattern during the day was constant in all seasons. The activity at dawn and dusk tended to be higher than that at day during July–October and July– November, respectively. Although the activity of sika deer may be influenced by weather condition, there was no seasonal consistency. Our study reveals that human disturbance might decrease diurnal activity and increase nocturnal activity.

A1-16 テフラ層序からみた中之島御岳火山の噴火活動史(口永良部火山・噴火史・火山災害,口頭発表)

A1-16 テフラ層序からみた中之島御岳火山の噴火活動史(口永良部火山・噴火史・火山災害,口頭発表)

Temporal changes in molar wear rate of a sika deer population under density‐dependent food limitation

AbstractNegative effects of density‐dependent food limitation on molar wear rate in ungulate populations, as well as unworn molar size and its sex differences in ruminants, have been studied for a long time. However, these studies were based on comparisons of populations from different districts or habitats. If drastic changes in food habits and life history occurred under density‐dependent resource limitation, it is of great interest whether this change caused temporal changes in molar wear rate, and whether the degree of hypsodonty changed under this short but intensive selective pressure. We examined the temporal change in molar wear rate using long‐term monitoring data of a sika deer (Cervus nipon) population on Nakanoshima Island, Hokkaido, Japan. Corresponding to the change in food habits, the molar wear rate changed mainly because of the amount of soil that was secondarily ingested when deer fed on fallen leaves. Molar wear rate was the fastest level after the first population crash on Nakanoshima Island among extant sika deer populations. Nevertheless, we did not find any evidence of increased hypsodonty in Nakanoshima deer. It is possible that natural selection for increased molar durability (hypsodonty) has been working on Nakanoshima deer, but the adaptive change has not yet appeared at a statistically significant level.

Occurrence of old groundwater in a volcanic island on a continental shelf; an example from Nakano-shima Island, Oki-Dozen, Japan

Summary Groundwater residence times in Nakano-shima Island, Oki-Dozen, Japan, which is situated on the continental shelf, are discussed based on groundwater-age indices (CFCs, 3 H, and 14 C), stable isotopic ratios of hydrogen (δD), oxygen (δ 18 O), carbon (δ 13 C), and noble gases ( 3 He/ 4 He and 4 He/ 20 Ne). Samples were taken from springs, shallow wells (up to 5 m deep), water-supply wells (about 10–100 m deep), and the hot spring well (866 m deep). δD and δ 18 O of all the samples plot along meteoric water lines, indicating a meteoric water-origin. Isotope values of the hot spring water were slightly lower than other samples. Most samples from springs, shallow wells, and the water-supply wells contained higher CFCs and 3 H while samples from two water-supply wells (W4 and W7) and the hot spring well showed much lower CFCs concentrations. This result indicates that mixing ratios of old groundwater that is free of CFCs and 3 H were higher for these samples. 14 C concentrations of samples with lower CFCs were measured, and corrected for addition of 14 C-free dissolved inorganic carbon. The corrected 14 C concentration of the hot spring water was lower than that of the water-supply well, indicating mixing of much older groundwater in the hot spring water. Because of lower corrected 14 C concentration and lower δD and δ 18 O values, groundwater from the hot spring well is considered to be recharged in a colder climate than present day. Because the island is situated on the continental shelf, the seafloor around the island was most likely widely exposed during the last glacial period. One possible explanation for the existence of groundwater showing lower δD, δ 18 O, and 14 C concentrations, such as the hot spring water, is that fresh groundwater, recharged when sea level was lower, still remains after transgression without being replaced by salt water.

Phylogeny and biogeography of Carminator (Hymenoptera: Megalyridae)

Carminator Shaw is a small genus of parasitic wasps that is mainly distributed in Southeast Asia. Eight species are recognized here, including Carminator coronatussp.n. and Carminator gracilissp.n. A data set comprising 54 morphological characters and including all the known species of Carminator, as well as four out‐group taxa (two Cryptalyra spp., one Ettchellsia sp. and one Megalyra sp.), was assembled and analysed. Carminator is retrieved as monophyletic. All weighted analyses place Carminator affinis as the sister group to the rest of the genus. A northern clade comprising species occurring on the Japanese Isles, Taiwan and Vietnam (Carminator japonicus (Carminator gracilissp.n. (Carminator cavus + Carminator helios))) is strongly supported and nested inside the more southerly distributed species. C. helios is found on Nakanoshima Island, which emerged post‐Pliocene, and so C. helios is considered to have dispersed there via a land‐bridge connection from the Ryukyu Islands. A key to all known species of Carminator is provided.

Toxicity and Toxin Profiles of Xanthid Crabs Collected around Nakanoshima, the Tokara Islands, Japan

A total of 36 specimens of 5 xanthid crab species, Zosimus aeneus (n=16), Xanthias lividus (n=4), Leptodius sanguineus (n=3), Daira perlata (n=10) and Eriphia sebana (n=3), were collected around Nakanoshima Island, which is located at the northeastern part of the Tokara Islands, Kagoshima Prefecture, Japan in May and July 2000, and their toxicity was determined by mouse bioassay. Nine of 16 Z. aeneus specimens and all of 4 X. lividus specimens showed lethal potency to mice (2.1-11 MU/g, 2.8-8.6 MU/g, respectively), whereas all the other species were non-toxic (less than 2.0 MU/g). LC/MS analyses indicated that the toxin of the Z. aeneus specimens was mainly composed of tetrodotoxin (41% of total toxicity), and 11-oxotetrodotoxin contributed to the remaining toxicity. The toxin of the X. lividus specimens, however, was apparently not tetrodotoxin. In HPLC-FLD analyses, no paralytic shellfish poison component was detected in either of the two toxic species.

Photosymbiotic Ascidians from Nakanoshima Island and Takarajima Island (the Tokara Islands, Ryukyu Archipelago, Japan) with Remarks on the Status of Diplosoma midori (Tokioka, 1954)*

We studied the fauna of photosymbiotic ascidians in the shallow reef shore of the Tokara Islands. We collected Lissoclinum bistratum, L. punctatum, Trididemnum clinides, T. cyclops, T. sp. (cf. T. paraclinides), Diplosoma ooru, D. simile, D. simileguwa, D. virens, D. sp. A, and D. sp. B (cf. D. multipapillatum) from four sites off Nakanoshima Island and one site off Takarajima Island. Diplosoma midori (Tokioka, 1954) is a photosymbiotic ascidian that was originally described from Nakanoshima Island and Takarajima Island. Although there is argument as to the taxonomical status of this species, the conditions of the syntype specimens were inadequate for examining detailed features for identification. Based on the topotype specimens from Takarajima Island, we concluded that D. midori should be regarded as an invalid species, and is a junior synonym of D. simile or D. virens.