Southern Shikoku Research Articles

Preface: Functional biogeography in Japanese cedar

Preface: Functional biogeography in Japanese cedar

Assessment of future precipitation indices in the Shikoku region using a statistical downscaling model

In this study, we used the statistical downscaling model (SDSM) to estimate mean and extreme precipitation indices under present and future climate conditions for Shikoku, Japan. Specifically, we considered the following mean and extreme precipitation indices: mean daily precipitation, R10 (number of days with precipitation >10 mm/day), R5d (annual maximum precipitation accumulated over 5 days), maximum dry-spell length (MaDSL), and maximum wet-spell length (MaWSL). Initially, we calibrated the SDSM model using the National Center for environmental prediction (NCEP) reanalysis dataset and daily time series of precipitation for ten locations in Shikoku which were acquired from the surface weather observation point dataset. Subsequently, we used the validated SDSM, using data from NCEP and outputs form general circulation models (GCM), to predict future precipitation indices. Specifically, the HadCM3 GCM was run under the special report on emissions scenarios (SRES) A2 and B2 scenarios, and the CGCM3 GCM was run under the SRES A2 and A1B scenarios. The results showed that: (1) the SDSM can reasonably be used to simulate mean and extreme precipitation indices in the Shikoku region; (2) the values of annual R10 were predicated to decrease in the future in northern Shikoku under all climate scenarios; conversely, the values of annual R10 were predicted to increase in the future in the range of 0–15 % in southern and western Shikoku. The values of annual MaDSL were predicted to increase in northern Shikoku, and the values of annual MaWSL were predicted to decrease in northeastern Shikoku; (3) the spatial variation of precipitation indices indicated the potential for an increased occurrence of drought across northeastern Shikoku and an increased occurrence of flood events in the southwestern part of Shikoku, especially under the A2 and A1B scenarios; (4) characteristics of future precipitation may differ between the northern and southern sides of the Shikoku Mountains. Regional variations in extreme precipitation indices were not notably evident in the B2 scenario compared to the other scenarios.

A phylogeographic study of the Japanese earthworm, Metaphire sieboldi (Horst, 1883) (Oligochaeta: Megascolecidae): Inferences from mitochondrial DNA sequences

To clarify the historical phylogeography of a Japanese earthworm, nucleotide sequence variations of Metaphaire sieboldi were investigated with respect to its geographic distribution. Sequencing of mitochondrial DNA (mtDNA), including the cytochrome oxidase subunit I (COI) region and the 16S rDNA region, of 72 samples including 4 outgroup taxa, and phylogenetic analyses using neighbour-joining (NJ) and Bayesian inference (BI) methods indicated that M. sieboldi forms a monophyletic group. This monophyletic group was divided into seven subgroups; most subgroups comprised individuals from several areas, except for southern Shikoku and southern Kyushu. The phylogenetic tree demonstrated that the Shikoku and Kinki populations were paraphyletic at the basal node, and individuals from Kyushu and western Shikoku were positioned at the advanced group. Estimated phylogeographic events based on mtDNA analyses include (1) M. sieboldi originated in Shikoku and/or Kinki, (2) individuals from Chugoku and Kyushu have a common ancestor from Shikoku, and (3) individuals from western Shikoku originated from Kyushu progenitors (about 0.4–0.5 mya) after separation by rising sea levels.

四国太平洋岸に共存するスナガニ属３種の季節的な分布パターンおよび食性

On sandy beaches of southern Shikoku, one temperate-zone crab, Ocypode stimpsoni, and two tropical and subtropical crabs, O. sinensis and O. ceratophthalma, co-occur, dwelling in individual burrows. Their distribution patterns, food habits, and physiological condition were investigated seasonally. Among the three species, O. sinensis was distributed in the highest zone vegetated with Vitex rotundifolia and Calystegia soldanella and was well segregated from the others except during its juvenile stage. It fed on terrestrial invertebrates and terrestrial plants. The distribution of O. ceratophthalma overlapped with that of O. stimpsoni; O. ceratophthalma mainly fed on terrestrial and aquatic invertebrates whereas O. stimpsoni fed on detritus and diatoms together with terrestrial and aquatic invertebrates. Ocypode ceratophthalma was poor in hepatopancreas index late in autumn and rarely overwintered, with the result that almost the entire population consisted of immature individuals. It is likely that the population of O. ceratophthalma in southern Shikoku is maintained by a supply of larvae from more southern regions. It is possible that O. stimpsoni, which is competitively inferior to O. ceratophthalma due to its smaller adult size, may become extinct in southern Shikoku if the recent rise in air temperature during winter enables more individuals of O. ceratophthalma to thrive there.

Effects of elevation and postharvest disturbance on the composition of vegetation established after the clear-cut harvest of conifer plantations in southern Shikoku, Japan

Large areas of previously clear-cut conifer plantations have been recently abandoned in Japan. We investigated the vegetation in the clear-cut sites and examined the environmental factors affecting species composition of the vegetation. We set up 32 study sites, each composed of several study plots (5 × 5m), ranging from 220m to 1060m a.s.l. Elevation and warmth index (cumulated thermal quantity) were the primary factors affecting the species composition, with clear-cut areas showing a smaller effect in the nonmetric multidimensional scaling (NMS) ordination. Two-way indicator species analysis (TWINSPAN) divided the 32 study sites into ten vegetation groups, clustering the sites by elevation or by postharvest disturbances (i.e., replanting or browsing of Sika deer). Deciduous trees and shrubs were significant in the vegetation cover at higher elevations, while they were less so in areas of high Sika deer populations. We also investigated the abundance of old-growth species, which are expected to regenerate where the clear-cut site is abandoned. Evergreen Quercus and Castanopsis saplings were abundant at low elevations (<600m), suggesting that they will successfully regenerate. The sapling densities of Abies firma and Betula grossa were significantly large where a clear-cut site was adjacent to natural forest, which is expected to act as a seed source. This implies that degraded deciduous forests may establish after clear-cutting at intermediate and high elevations (>600m) if the clear-cut site is distinct from seed sources. It is argued that the preservation of natural forests is critical for the regeneration of old-growth species.

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.

Growth of the fourspine sculpin Cottus kazika in the Gonokawa River, Japan, and effects of water temperature on growth

The fourspine sculpin Cottus kazika is indigenous to Japan and found in Honshu except for the waters facing the Seto Inland Sea, and was also found in southern Shikoku and eastern Kyushu. This species has a catadromous life style and migrates as juveniles from the sea to the middle reaches of rivers to grow. The growth pattern of this fish was investigated by a mark-and-recapture method from July 1994 to December 1996, in the Nigorikawa River, a tributary of the Gonokawa River system, Shimane Prefecture. 0-year-old fish of 50–70 mm total length (TL) occurred in the study area from June to July, grew to 90–140 mm TL by the following April, and attained 160–210 mm TL by December. This fish grew rapidly in September–November and April–July, almost ceasing to grow in July–September. It seems that this stagnant growth phase in summer is a characteristic of the seasonal growth pattern of C. kazika. A rearing experiment indicated that the growth rate of C. kazika was higher at 16–22°C than at 12–14 and 24–26°C. This result supports the field evidence of a stagnant growth phase in summer in the Nigorikawa River.

Reproductive phenology of sympatric hermit crabs in temperate Japan

Reproductive phenology among temperate hermit crabs, reproductive seasons of nine sympatric species and some reproductive characteristics of four Pagurus species were investigated in Tosa Bay, southern Shikoku, Japan. Females of P. filholi, P. maculosus, P. minutus and P. nigrivittatus had clutches mainly in winter and were found to breed multiple clutches within each reproductive season while four Diogenidae species and P. japonicus mainly reproduced in summer, suggesting that interspecific variation in reproductive phenology of temperate hermit crabs might be determined by allopatric adaptation with phylogenic constraints. There was interspecific variation in the length of reproductive seasons among the four Pagurus species and the variation was considered to reflect the interspecific difference in the number of clutches per reproductive season, not in the ovigerous period per clutch. The length of reproductive seasons among the four species seemed to relate to maturity size and/or interspecific differences in thermal adaptation.

Configuration of subducting Philippine Sea plate beneath southwest Japan revealed from receiver function analysis based on the multivariate autoregressive model

We construct a detailed image of velocity discontinuity beneath southwest Japan by using receiver functions. We first propose an improved receiver function estimation method based on the statistical multivariate autoregressive model. Then we apply the new method to the teleseismic waveform data recorded by the high‐density seismograph network in southwest Japan. The results show a clear velocity discontinuity at 30 km depth beneath the southern Shikoku region. This discontinuity, corresponding to the boundary between the oceanic crust and the high‐velocity layer (the oceanic Moho) of the Philippine Sea plate (PHS), continues down to the north indicating that the aseismic PHS extends to the central Chugoku region. The continental Moho is also clearly imaged beneath the Chugoku region. The depth contour of the PHS shows a rather complicated feature with ridges and valleys. The most significant ridge is located around longitude 133°E, west of which the contours are basically directed north‐south, changing to west‐east to the east. Beneath the western part of this ridge, hypocenters of microearthquakes are located above this velocity discontinuity, while earthquakes mainly occur below the discontinuity, within the oceanic mantle, beneath the eastern part of the ridge.

A new species: Gerres microphthalmus (Perciformes: Gerreidae) from Japan with notes on limited distribution, included in the " G. filamentosus complex"

Gerres microphthalmus sp. nov., described on the basis of the holotype and 38 paratypes, has a limited distribution in Japan, including Tanega Island, southeastern Kyushu, southern Shikoku, and southern Kii Peninsula, central Honshu. It has not been recorded from the Ryukyu Islands. The species is the fourth member of the “G. filamentosus complex,” characterized by an elongated second dorsal fin spine, the others being G. filamentosus, G. infasciatus, and G. macracanthus. Gerres microphthalmus sp. nov. is most similar to G. filamentosus in overall body appearance, but differs from the latter in having smaller eyes (8%–11% of standard length vs. 10%–16% in the latter), a higher orbit diameter ratio (as % of snout length) (93%–143% of snout vs. 71%–104% of snout), and fewer pored lateral line scales (40–43 vs. 43–46). The limited distribution pattern of the new species is discussed with G. equulus and Lates japonicus (Centropomidae) having a limited distribution similar to that of the new species.

Two alternative female tactics in the polygynous mating system of the threadsail filefish,Stephanolepis cirrhifer (Monacanthidae)

Reproductive behavior of the threadsail filefishStephanolepis cirrhifer was studied at Kashiwajima, southern Shikoku, Japan. This species spawned in pairs on the sandy bottom, the eggs being scattered over an area of about 15 cm in diameter and attached to sand particles. After spawning, males departed immediately, while the females remained at the site to guard the eggs for a few minutes. Thereafter the eggs were left unguarded for three days until hatching. Females spawned only once daily, whereas males mated with multiple females in succession. The reproductive males established territories, in which 1–4 resident females defended smaller territories from each other. The harem size changed according to some ecological conditions, such as population density. Moreover, the males also mated with visiting non-resident females. Thus, the two alternative tactics of females resulted in two mating patterns, haremic polygyny and female visiting of male territories, in a single population ofS. cirrhifer.

Crustal movements on Shikoku, southwestern Japan, inferred from inversion analysis of levelling data using ABIC

With an inversion technique based on Akaike's Bayesian Information Criterion (ABIC) we analyzed levelling data for 1893–1983 on Shikoku, southwestern Japan, where large interplate earthquakes have periodically occurred at intervals of about 120 years, releasing tectonic stress produced by steady relative motion of the Philippine Sea and the Eurasian plates. Through the inversion analysis we reconstructed the pattern of crustal movements on Shikoku over the last 120 years, including the occurrence of the 1946 Nankaido earthquake ( M 8.1). The result clearly shows that the crustal movements on Shikoku include significant secular vertical motion (uplift in the south and subsidence in the north) in addition to cyclic motion related to the periodic occurrence of interplate earthquakes at the Nankai trough. Contrary to the widely accepted theory, we could not find any correlation between the secular vertical motion and the coseismic vertical displacement. The secular uplift motion on southern Shikoku estimated from the levelling data completely agrees with that inferred from the present heights of marine terraces formed by eustatic sea level changes and crustal uplift for the last 10 5 yr. This suggests that the fundamental causes of the short-term (10 2 yr) and long-term (10 5 yr) movements on southern Shikoku are the same, the steady subduction of the Philippine Sea plate at the Nankai trough. On northern Shikoku, on the other hand, the pattern of secular crustal motion estimated from the levelling data is quite different from that of the Quaternary uplift inferred from the present heights of eroded flat surfaces, indicating the existence of some unknown tectonic process controlling the very long-term (10 6 yr) crustal movements.

Estimation of crustal structure in central and west Japan from waveform modeling of regionalPL waves

An inverse method of modeling the regionalPL waveform with the predominant period of about 20 s was developed to estimate the averageS-velocity structure of the upper crust. Applicability of the waveform modeling was confirmed by the results of the numerical experiments: thePL waveform is most sensitive to theS velocity in the upper crust, whereas it is not affected significantly by errors involved in the focal mechanism solution and focal depth determination when thePL wave is well developed. The method was applied to the observed seismograms recorded in central Japan from the earthquakes with epicentral distances 300–500 km. As a result, distinct regional differences were found in the upper crustalS velocity; in particular, between the southern Shikoku district, west Japan, and the southern Chubu district, central Japan, and between the mountainous and the coastal areas in the southern Chubu district. These differences are in agreement with the general features ofP-velocity structures obtained by explosion experiments and by analyses of natural earthquakes. Our method is effective to the extent that the crustal structure along the propagation path can be assumed a horizontally layered structure; it is not applicable when the sensitivity of thePL waveform to the error in the focal mechanism solution is exceptionally high.

An analysis of split shear waves observed above crustal and uppermost mantle earthquakes beneath Shikoku, Japan: Implications in effective depth extent of seismic anisotropy

Shear wave splitting has been detected in three‐component seismograms from a number of small earthquakes taking place either within the upper crust or the uppermost mantle beneath the Shikoku area, Japan. The faster shear waves are polarized nearly in E‐W at the stations in the central part of Shikoku, and in NEN‐SWS at the southern stations. The arrivals of slower shear waves polarized orthogonally to the faster ones are also clearly recognized in many seismograms at one of the stations. The faster shear wave polarizations at the stations in the central part of Shikoku and the pattern of travel time differences between split shear waves are successfully explained in terms of crustal anisotropy generated by vertical alignment of stress‐induced microcracks. The difference in polarization directions suggests that the tectonic stress state beneath the southern Shikoku region is significantly different from that beneath the central part of Shikoku. A quantitative analysis of travel time differences between split shear waves suggests that the presence of seismic anisotropy which causes the observed shear wave splitting is limited to the upper 10 or 15 km of the crust. Nevertheless, the possibility that anisotropy is concentrated in a much thinner surface layer cannot be ruled out. The average aspect ratio of crack might be greater than of the order of 10−2, or the cracks may not be purely vertical but have some fluctuations in the dip angle.

四国南部沈降地域の海岸低地堆積物にみる完新世後半の二つの時期の古海水準

四国南部沈降地域の海岸低地堆積物にみる完新世後半の二つの時期の古海水準

The early research of biostratigraphy in Japan with special reference to the geology of southern Shikoku

The early research of biostratigraphy in Japan with special reference to the geology of southern Shikoku

Clinical aspects of adult T-cell leukemia/lymphoma.

Since adult T-cell leukemia (ATL) was first proposed as a new disease by Takatsuki and associates (Takatsuki etal. 1977; Uchiyama etal. 1977) in Kyoto, we estimate that more than 500 patients with ATL have been detected so far in Japan. Most of them are from Kyushu, the southernmost island of Japan, although the disease is also endemic in southern Shikoku and some parts of Honshu, including Sadogashima, an island near Niigata, and Ishinomaki, an area on the north of Sendai.KeywordsChronic Lymphocytic LeukemiaMycosis FungoidesSezary SyndromeAcute Monocytic LeukemiaPeripheral Lymph Node EnlargementThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

DISTRIBUTION AND ITS CHANGE OF PRODUCTIVITY OF AGRICULTURAL LAND IN JAPAN, 1960-1975

The purpose of this study is to present the meso-scale distribution of productivity of agricultural land (P. A. L.) in Japan and its change during the period from 1960 to 1975. P. A. L. is defined as gross product (thousand yen) of agriculture per agricultural land. The gross product of processed agricultural products were, however, excluded from the figure. The data for gross product of agriculture are obtained from the statistics on the agricultural income published by the Ministry of Agriculture, Forestry and Fishery. The book includes the amounts of products such as rice, wheat, barley, other cereals, peas, beeps, potatoes, sweet potatoes, vegetables, fruits, industrial crops, flower, sapling, and livestock. Agricultural lands includes cropland, orchard, pasture, and grassland pasture. These data for the analysis in 1960, 1965, 1970 and 1975 are taken from the Agricultural Census of Japan. The study area covers entire Japan excluding Okinawa prefecture due to the unavailability of data. The whole area is divided into 305 unit districts (Fig. 1), general nature of which were fully examined by Birukawa et al. (1964). The first step of the analysis was the preparation of maps of P. A. L, in each year. Then, the change of cereal distributions of P. A. L. were investigated by comparing these series of maps one another. Subsequently, the polynominal trend surface analysis was applied for analyzing the general distribution pattern and the change from 1960 to 1975. The general pattern of P. A. L. for each polynominal degree in each year, was also analyzed. In addition, the general patterns of P. A. L, were classified into types, and the residuals were considered as local components. The maps of standardized P. A. L. shows high scores in the fringe area of the metropolitan areas facing the Pacific Ocean and areas facing the Inland Sea, while low scores are in the several areas in the remote and secluded districts of Hokkaido, and the areas facing the Japan Sea (Fig. 2). It is clear that the difference in scores between the districts facing the Pacific Ocean and those facing the Japan Sea increased from 1970 to 1975. The number of areas with very high score increased significantly from 1965 to 1970. As a result, the number of districts with very high score is twice as numerous in 1970 compared to 1960. The increasing rate of areas with high score has been gradually getting higher. The number of districts with medium score decreased drastically from 1965 to 1970, and this tendency continued untill 1975. On the other hand, districts with low score gradually increased in number. Thus in 1975, there are 33 additional districts with lowscore compared with 1960. Regional variation of standardized P. A. L, has decreased in the recent census (Fig. 3). The types of change of P. A. L. gradually increased in number during this period, and the patterns of the change have been diversified. Fig. 4 shows the fitness of the trend surface to P. A. L.. There is a tendency of gradual increase of fitness from the first to the fifth degree in each year of analysis. Except for 1960, the fitness decreases at the 6th degree, and sharply increases in the 7th degree. Judging from maps of each year, the fitness in 1965 generally showed the low percentage, while the percentage were high in 1970. Comparing the results of variance analysis (Table 1) with the change of fitness of P. A. L., the general distribution patterns are investigated in this paper, at the 8th degree for 1960, and at the 7th degree for the remaining 3 census years (Fig. 5). The inspection of this figure shows the regions of maximum on the trend surface extending from Osaka to eastern and southern Shikoku, and from Tokyo to Shizuoka prefecture, and the region centered around Akita.

Observations of thermal microstructure in the Kuroshio off of Southern Honshu and Shikoku

Direct observations of thermal microstructure within the main stream of the Kuroshio show that within the region of the most steeply sloping isotherms, from about 180 to 360 m depth near the current axis, considerable microstructure is present, and the laminae tend to be approximately aligned along the sloping isothermal surfaces rather than horizontally. Away from the axis, the slopes of the isotherms are considerably less so that the tendency for alignment along isotherms, if present, is not noticeable. Laminae rarely if ever extend for as much as 6 miles in the cross-current direction. Lateral temperature variations within individual laminae are small; to the extent that they do occur there is no apparent tendency for density to be conserved.

Types of the Development of Coastal Cities in Chûgoku and Shikoku Districts

Along the coasts of Chugoku and Shikoku districts, there are numerous cities with different historical backgrounds offering good examples for the analysis of the types of coastal cities. The writer selected 21 cities in these districts, and induced the regional types of their developments according to the periods in which the cities were founded, and to their relation with such factors as the construction of castles, the development of ports and railway stations. They are summarized as follows.1) The coastal cities in Southern Shikoku are backward in development.2) In Sanyo district, in accordance with the development of deltas, cities extended toward the coast after the construction of castles in feudal days.3) In Northern Shikoku, the castles are generally located on the coast, and the cities developped inland from the coast.4) The difference in the development of cities between Sanyo district and Northern Shikoku are because in the former area the deltas are generally big and rapid in growth, while in the latter they are small and slow in growth.