Western Chugoku Research Articles

Ecological niche modeling shed light on new insights of the speciation processes and historical distribution of Japanese fire-bellied newt Cynops pyrrhogaster (Amphibia: Urodela)

Environmental factors play vital roles in determining the range of organisms and application of selective pressures that drive their evolution. Investigation of how these ecological factors influence the diversification of species has long been a point of interest among ecologists. In this study, we used climate-based ecological niche models to project the suitable distributions of four main clades of Japanese fire-bellied newt Cynops pyrrhogaster at the Last Glacial Maximum (LGM), Mid-Holocene (MH), and the present. Then we tested hypotheses regarding ecological niche diversification and the processes of diversification among these clades. The potential distribution of the Northern clade encompassed the Tohoku and Kanto districts, along with the northeastern Chubu district. The Central clade had a potential distribution across the Chubu and Kinki districts, and northeastern Chugoku district. The range of the Western clade was projected to encompass Kyushu, Shikoku, the southern Kinki region, and western Chugoku. Finally, the projected distribution of the Southern clade was limited to the southern Kyushu district. The lack of equivalent niches among the tested pairs indicated the absence of ecological interchangeability among the clades. The results of a similarity test supported significant parapatric divergence of the Northern and Central clades from the remaining clades. On the other hand, the Western and Southern clades probably underwent divergence through an allopatric process. Our paleomodels suggest that the distribution of C. pyrrhogaster may have been reduced and fragmented along the coastal regions during the LGM. The distribution models for the MH estimated a suitable area larger than for the LGM, but smaller than predicted by the current distribution. Our findings serve as a warning that the potential distributions of species could be significantly influenced by future climate change.

Preface: Functional biogeography in Japanese cedar

Preface: Functional biogeography in Japanese cedar

An evaluation of camera trap study and a New Management Plan for Japanese black bears in the western Chugoku Areas, Japan

An evaluation of camera trap study and a New Management Plan for Japanese black bears in the western Chugoku Areas, Japan

A high‐Tmetamorphic complex derived from the high‐PSuo metamorphic complex in the Omuta district, northern Kyushu, southwest Japan

AbstractNew U–Pbages of zircons from migmatitic pelitic gneisses in the Omuta district, northern Kyushu, southwest Japan are presented. Metamorphic zonation from the Suo metamorphic complex to the gneisses suggests that the protolith of the gneisses was the Suo metamorphic complex. The zircon ages reveal the following: (i) a transformation took place from the high‐PSuo metamorphic complex to a high‐Tmetamorphic complex that includes the migmatitic pelitic gneisses; (ii) the detrital zircon cores in the Suo pelitic rocks have two main age components (ca1900–1800 Ma and 250 Ma), with some of the detrital zircon cores being supplied (being reworked) from a high‐grade metamorphic source; and (iii) one metamorphic zircon rim yields 105.1 ±5.3 Ma concordant age that represents the age of the high‐Tmetamorphism. The high‐Pto high‐Ttransformation of metamorphic complexes implies the seaward shift of a volcanic arc or a landward shift of the metamorphic complex from a trench to the sides of a volcanic arc in an arc–trench system during the Early Cretaceous. The Omuta district is located on the same geographical trend as the Ryoke plutono‐metamorphic complex, and our estimated age of the high‐Tmetamorphism is similar to that of the Ryoke plutono‐metamorphism in the Yanai district of western Chugoku. Therefore, the high‐Tmetamorphic complex possibly represents the western extension of the Ryoke plutono‐metamorphic complex. The protolith of the metamorphic rocks of the Ryoke plutono‐metamorphic complex was the Jurassic accretionary complex of the inner zone of southwest Japan. The high‐Pto high‐Ttransformation in the Omuta district also suggests that the geographic trend of the Jurassic accretionary complex was oblique to that of the mid‐Cretaceous high‐Tmetamorphic field.

K-Ar Ages of Andesites from Two Volcanic Arrays in Western Chugoku, Southwest Japan

The volcanic front in the Southwest Japan Arc formed relative to the subducting Philippine Sea Plate. In the west Chugoku district, the volcanic front changes direction from E-W to NNE-SSW. Twenty-two Quaternary lava domes in this area can be topographically classified into two arrays (East and West arrays) based on the degree of dissection. K-Ar age results show that domes of the East array formed earlier (0.6-0.3 Ma) than those of the West array (0.2 Ma-recent). The two arrays in different ages may result from the migration of volcanic front caused by westward migration of the PSP slab.

Late Cretaceous ignimbrite flare-up in the eastern margin of Asian Continent: an example of western Chugoku caldera cluster

Late Cretaceous ignimbrite flare-up in the eastern margin of Asian Continent: an example of western Chugoku caldera cluster

IV. The progress and issues on the Specified Wildlife Conservation and Management Plan for Japanese black bears in the western Chugoku Mountains, Japan

IV. The progress and issues on the Specified Wildlife Conservation and Management Plan for Japanese black bears in the western Chugoku Mountains, Japan

Distribution of moist beech forests on mountain tops and their habitat conditions in the western Chugoku Mountains, Japan

Distribution of moist beech forests on mountain tops and their habitat conditions in the western Chugoku Mountains, Japan

The present status and issues of the Specified Wildlife Conservation and Management Plans for the Asiatic black bear in the western Chugoku Mountains, Japan

The present status and issues of the Specified Wildlife Conservation and Management Plans for the Asiatic black bear in the western Chugoku Mountains, Japan

Topography of the Seismic Velocity Discontinuities beneath the Chugoku and Shikoku Districts, Southwest Japan

The first P-arrival-time data from 513 local earthquakes were analyzed to study lateral variation of the depth to the Conrad and Moho discontinuities beneath the Chugoku and Shikoku districts, southwest Japan, as well as to determine earthquake hypocenters and P-wave station corrections. The depth to the discontinuity was estimated by minimizing the travel-time residuals of more than 8700 first P arrivals observed at 55 seismic stations. The Conrad and Moho discontinuities are located within depth ranges of 15–25 km and 30–40 km, respectively. The Moho is deeper under the mountain area than under the Seto Inland Sea area, and especially deep under the Pacific Coast of the Shikoku district and the mountain area in the Chugoku district. The depth variation of the Moho is quite similar to the Bouguer gravity anomaly distribution and the lateral variations of the P-wave velocity. The deep Moho under the southern Shikoku is located at the portion in which the continental Moho under the island arc meets the oceanic Moho that is the boundary interface between the oceanic crust and the Philippine Sea (PHS) plate dipping toward the back arc. Although there are high mountains in the northern and middle Shikoku, the Moho is not so deep because subduction of the PHS plate prevents the Moho from getting deep, while the Moho is deep due to isostatic balance under the mountain area in the Chugoku district. In addition, we indicated the possibility that the upper boundary of the oceanic crust just above the high-velocity PHS plate is in contact with the deep Moho under the western Chugoku. The contact of the Moho with the oceanic crust can explain the markedly negative gravity anomaly observed in the western Chugoku and the later phase that appears just after the first P arrival from local earthquakes.

Distributed strike-slip faulting, block rotation and possible intracrustal vertical decoupling in the convergent zone of SW Japan

Abstract Between the Median Tectonic Line (MTL) and the Japan Sea, the western Chugoku region of SW Japan is cut by a series of N45°E first-order faults and oblique (N60°–N170°E) second-order faults. This fault network, probably formed during Late Cretaceous-Palaeocene times (70–60 Ma), defines a regional block structure. Pre-Plio-Quaternary kinematical indicators suggest left-lateral motion along the first-order faults and right-lateral motion along some of the second-order faults. Geomorphological evidence and earthquake focal mechanisms indicate that Plio-Quaternary slip senses are opposite to Pre-Plio-Quaternary ones. The overall fault pattern is geometrically and kinematically similar to patterns obtained by experimental modelling of simple shear deformation distributed at the base of a brittle layer analogue over its entire width. This similarity suggests the possibility of a mid-crustal, flat-lying partial attachment zone which could have controlled the formation of the western Chugoku fault network in Cretaceous to Palaeocene times. The zone, presently inactive, could correspond to the ‘proto-MTL’, a low-angle fault recently imaged by seismic reflection studies and whose trace approximately coincides with the present-day MTL. Reactivation of the system occurred twice after its formation: firstly in Miocene times, during the opening of the Japan Sea and concomitant clockwise rotation of the entire SW Japan arc; and secondly in Late Pliocene to Quaternary times, after a shift of the relative direction of convergence between the Philippine and Eurasia plates. Unlike the first reactivation, the second reactivation led to an inversion of the sense of slip along the faults.

High resolution receiver function imaging of the seismic velocity discontinuities in the crust and the uppermost mantle beneath southwest Japan

Clear images of the seismic velocity discontinuities in the crust and the uppermost mantle beneath southwest Japan have been obtained with Receiver Function (RF) analyses of teleseismic waveforms observed at extraordinary dense short-period and broadband stations. For imaging, we construct several 2-D profiles of depth-transformed RFs to delineate the fine crustal structure and the 3-D configuration of the Philippine Sea plate (PHS). The Moho is clearly seen and locally depressed just beneath the Chugoku Mountains. The Conrad, the velocity discontinuity within the crust, in the northern Kinki region is recognized and depressed just beneath the Chugoku Mountains as well as the Moho. RF analyses also clearly elucidate the largely contorted configuration of the PHS including aseismic portions. The PHS subducts aseismically under the western Chugoku region with a high dip angle of 35 degrees at least to a depth of 65 km. In the western Kii Peninsula, it descends steeply to a depth of 90 km with some curvature, while it subducts with a low dip of 20 degrees to a depth of 60 km from the eastern Kii Peninsula to the Lake Biwa.

Subduction of young plates: A case of the Philippine Sea plate beneath the Chugoku region, Japan

An analysis of seismic waves from regional microearthquake networks shows that the seismic leading edge of the Philippine Sea plate may have reached the uppermost mantle beneath the southern to central part of the western Chugoku region, Japan. The epicenters are located close to the volcanic front in the region. The most possible cause of the very low seismicity may be the initiation of melting of the Philippine Sea plate.

Genetic status of fragmented populations of the Asian black bear Ursus thibetanus in western Japan

AbstractThe population genetic status of the Asian black bear Ursus thibetanus in the western part of Japan was examined using microsatellite DNA markers. Although three fragmented populations have been recognized in this region, i.e., the western Chugoku (WC), eastern Chugoku (EC), and northern Kinki (NK) populations, it was recently pointed out that the NK population has also been divided into two subpopulations, the western (WNK) and the eastern (ENK) populations. We examined the genetic status of these four populations based on their heterozygosities and the genetic distances (FST) between them. The mean observed heterozygosity, i.e., genetic diversity, of the six microsatellite loci examined, was significantly lower in WC (0.272; n = 52) and WNK (0.311; n = 66) than that in ENK (0.445; n = 67), respectively. Reflecting geographic distances among populations, FST was higher between WC and WNK (0.244) and between WC and ENK (0.229) than that between WNK and ENK (0.066), respectively. There was also low but significant genetic differentiation between the two nearest populations (WNK and ENK). Although the status of EC was not conclusively determined because of its small sample size (n = 24), its genetic diversity seemed to be at a level similar to that of WC and WNK. These results suggest that WC, which is isolated from the others, has been losing genetic diversity, and that WNK, which had been thought to form a relatively large population together with ENK, might be isolated genetically from other populations. WNK, as well as WC and EC, should be conserved intensively.

Intrusion and differentiation of the Tsubashiki diorite stock in the western part of Yamaguchi Prefecture, S.W. Japan. Formation of the stock through fractional crystallization and filter-pressing under a hydrous condition.

The Tsubashiki diorite body in the western part of Yamaguchi Prefecture, Southwest Japan, is a small stock, with comagmatic dikes of various rocks. It is composed of melanocratic hornblende diorite and mesocratic hornblende quartz diorite, with hornblende-pyroxene diorite intruding them. Comagmatic mafic and felsic dikes are accompanied with the diorite stock. The mafic dikes are composed of pyroxene andesite, hornblende andesite and hornblende porphyrite. The felsic dikes are mainly composed of hornblende-bearing rocks of tonalite, granodiorite and granite, with minor quartz porphyry. Enclaves of andesitic and dioritic rocks occur in some felsic dikes. The SiO2 content ranges from 52 to 59 wt.% in the diorite stock, from 55 to 56 wt.% in the mafic dikes, from 60 to 74 wt.% in the felsic dikes and from 55 to 59 wt.% in the andesitic enclaves. The diorite stock, mafic dikes and the andesitic enclaves are rich in K2O, while the felsic dikes are poor in K2O and rich in Na2O. Whole rock K-Ar ages are 82.8±1.8 Ma for the hornblende-pyroxene diorite in the diorite stock and 77.3±1.7 Ma for the biotite-hornblende granodiorite in the felsic dike, indicating the last stage in the Sanyo-type plutonic activities during Cretaceous in the western Chugoku district. From field relations, modes of occurrence, petrographical features, K-Ar ages and chemical compositions, it is suggested that the Tsubashiki diorite stock was formed by intrusion of a basic andesitic magma under the condition of increase of water and by slight fractional crystallization of ferromagnesian minerals in the hydrous magma. It is also suggested that the mafic dikes were derived from the undifferentiated basic andesitic magma, and that the felsic dikes were formed through filter-pressing differentiation of the residual liquids with magma mixing during the process of cooling of the stock.

西中国山地・広島県加計町における過疎化と集落システムの変動

本稿では,早くから過疎化の進んだ中国山地西部の1山村・広島県加計町を対象に,その集落システムの変動を,人口変化,中心機能の集積,地域労働市場の展開の3つの側面から検討した.その結果,この約30年間にその集落システムは大きく変化したことが明らかとなった.集落別の人口変化(1960～1990年)では標高の重要性が確認され,過疎化は近接性に欠ける高位集落でとくに激しく進行したことが判明した.人口の分布はしだいに低位集落に収斂する傾向にある.中心機能からみた現在の集落システムの構成は,中心部が商業機能,公的機関の面で集積が著しく,その卓越性は,公共施設の配置,学校の統廃合を通じてさらに強化されている.その一方で支流部低位集落や高位集落では明瞭な中心集落を欠く.地域労働市場の面では,中心部集落が公的機関の統廃合による労働市場縮小の影響を受け,他方,高度経済成長期以降町内に分散立地した工場は,周辺部集落のそれを中心に今や海外や国内他地域との競争や労働力の高齢化によって岐路に立っている.今後の山村政策は,こうした集落レベルの変動に対応することが大きな課題となろう.

Survey of the amputee in the northern Kyushu and western Chugoku districts

Survey of the amputee in the northern Kyushu and western Chugoku districts

The Questionnaire Survey of Japanese Macaques in the Western Chugoku District; Yamaguchi, Shimane and Hiroshima Prefectures

Questionnaire surveys have been made sporadically since 1973 in the southern Chugoku district. In some areas wild monkeys were observed directly and/or studied in more detail by asking local people. The results are presented here and compared with those of Hasebe (1923), Kishida (1950) and Takeshita (1962). The description in an older document, Bohchoh-Fudoki (1841), is also referred to in the case of Yamaguchi Prefecture.

徳佐盆地（山口県）における後期更新世の花粉分析 （予報）

The Tokusa Basin is situated at an elevation of 300m in the northeastern part of Yamaguchi Prefecture in the western Chugoku Mountains, western Japan. A 68m long core containing silt, peat, volcanic ash and clay, which accumulated in the old lake Tokusa during Pleistocene, was sampled at Tokusa-Sadayuki, Ato-cho, in the Basin.In the study reported in this paper, a part of the 68m long core: 10.6m were palynologically examined at intervals of 20cm. Three samples were measured by 14C dating method: the age of the middle samples (390-395cm) was 46, 110±1, 050y. B. P. The volcanic ash inbedded between 500 and 520cm was estimated as Aso-4 ash which accumulated in the old lake ca. 70, 000 years ago.From the results of pollen analysis from the Tokusa Basin and the Ubuka Basin (HATANAKA and MIYOSHI, 1980), seven pollen zones could be recognized; in order from the surface to the lower part, they are as follows:L zone (10, 000-15, 000y. B. P.) with subarctic pollen types (Pinus, Abies, Picea, Tsuga, Betula)P-I zone (15, 000-25, 000y. B. P.) with subarctic pollen types (Pinus, Abies, Picea, Tsuga)P-II zone (25, 000-45, 000y. B. P.) with subarctic pollen types (Pinus, Abies, Picea, Tsuga, Betula)P-III zone (45, 000-70, 000y. B. P.) with temperate pollen types (Cryptomeria)P-IV zone (70, 000-80, 000y. B. P.) with cool temperate pollen types (Fagus, Quercus, Tsuga, Picea)P-V zone (80, 000-120, 000y. B. P.) with cool temperate pollen types (Fagus, Quercus, Carpinus, Ulmus)P-VI zone (120, 000-?) with temperate pollen types (Cryptomeria, Tsuga, Pinus, Carpinus) L and P-I zones are from the Ubuka Basin, P-II and P-VI zones from the Tokusa Basin.The six pollen zones from L to P-V cover approximately the 110, 000 years of the last glacial period, while the P-VI zone is a part of the last interglacial period.

Settlement and Field Pattern in the Upper Reaches of the Ota River, Western Chugoku Mountains

Settlement and Field Pattern in the Upper Reaches of the Ota River, Western Chugoku Mountains