A dense population of a salmon-like fish, Plecoglossus altivelis, or"Ayu"in Japanese, is found in the River Ukawa on the Japan Sea coast of Kyoto Prefecture. Members of our research group have been studing the ecology of this fish from various viewpoints since 1955. This paper concerns the change of the social behaviour and the mode of production. As already reported by our group, the common habit of this fish is territorial in the river-rapids and schooling in the river-pools. But on certain occasions, it shows no territorial behaviour, even in the river-rapids. By my recent observation, the social type of this fish appears to change with reference to the population density, and this change is accompanied by the difference in the body-length distribution. Five types were recognized in its social behaviour : schooling, solitary travelling, non-territorial solitary residential, solitary territorial and aggregated. The schooling is a social type in which all the members of a group show common behaviours, swimming in the same direction and feeding in similar manner. Solitary traveller is an independent passenger, having no home, but it may be united with a school or may be separated again. Non-territorial resident is a solitary dweller having its own range but does not show the territorial or attacking behaviour to the nearby individuals. In the territorial solitary type each fish has its own territory. An aggregation means that its members are aggregated within a certain area but do not show the common behaviour, and this type of behaviour is observed when they are resting or sleeping. The population of this fish, by our estimation, was far less in 1956 than in 1955(about one sixth), and the social relationship seemed to have been influenced by it. In 1955,when the density was high, most fishes showed the schooling behaviour and the territorial ones were very scarce. On the contrary, in 1956,when the density was low, many fishes behaved as settled solitaries and territorial individuals were not scarce. The stability of the school and the territory differs according to the change of population density. In the high density, the schooling is the common and more stable behaviour type of this fish and no difference is seen in the bodylength between the schooling and terrtorial ones. In the low density, however, the territorial behaviour is more stable, and there occurs a difference in the body-length, i.e. the territorial fishes are much larger than the schooling ones. In the case of the social structure in which the fishes are stabilized with territoriality, the growth of the non-territorial fishes seems to be checked because the latter cannot invade the bottom of the first class, which is defended by territorial fishes.
Peanut seeds (Arachis hypogaea L.) treated at 25℃, 15℃, and 5℃ for ten days were seeded together with a non-treated control, in spring 1956. 1) The 25℃-treated group and the 15℃-treated group promote the flowering compared with the control. There is no difference between the 5℃-treated group and the control. So it is appears that the peanut may pass through the vernalization phase at temperatures ranging from 15℃ to 25℃. 2) The 25℃-treated group and the 15℃-treated group have about 10 per cent more yield (pod-weight) than the control. But the cause of the increased yield is different between the 25℃-treated group and the 15℃-treated group ; in the 25℃-treated group mainly it is because the pods grow richer and heavier, while in the 15℃-treated group it is because the pod-count in one plant increases. There is no difference between the 5℃-treated group and the control. 3) In the 25℃-treated group and the 15℃-treated group, the fatty oil content in seeds increases a little, and the specific gravity of fatty oil, the Iodine Value and the acidity decreases slightly, compared with the control. Perhaps these may depend on the fact that by means of the vernalization, the 25℃-treated group and the 15℃-treated group promote their development compared with the control. There is no difference between the 25℃-treated group and the 15℃ treated group, nor between the 5℃-treated group and the control.
1. Everywhere in Hokkaido, we can see many waste lands, such as plains, abandoned cultivated fields and borders of arable lands overgrown with many weeds. Not only such waste lands, but even arable lands, new reclaimed lands and afforested lands are overgrown with various kinds of weeds making their own characteristic communities. 2. The writer tried to divide such weed communities, into several types which grow on cultivated, new reclaimed and abandoned fields, according to the dominant species of the communities, their habitats and succession, as follows. A. Weed community-types in the cultivated field and its habitat and the most luxuriant season of communities. (1) Acalypha-type ; Loam, Vegetable garden, from summer to autumn. (2) Stellaria media-t. ; Fertile soil, Vegetable garden and orchard field, from early summer to early winter. (3) Sperguld-t. ; Loam, flax field, from summer to autumn. (4) Portulaca-t. ; Sandy loam, Vegetable garden, from summer to autumn. (5) Chenopodium-t.; Loam, Potato or soy beans field, Autumn. (6) Polygonum-t. ; Loam, Wheat field, Autumn. Main species ; Polygonum logisetum, P.nodosum, P.longisetum forma albiflorum. (7) Polygonum nepalense-t. ; All over the cultivated field, Autumn. (8) Commelina-t. ; Loam, Potato or wheat field, from summer to autumn. (9) Gramineae-t. ; The species of gramineae growing in the cultivated field of this type are : Setaria autumnalis, S. viridis, S. pumila, Echinochloa Crus-galli, Digitaria adscendens, D. violascens, Panicum bisulcatum, Dactylis glomerata, Phleum paniculatum etc. (10) Equisetum arvense-t. ; Sandy loam, Vegetable garden or orchard field, from summer to autumn. (11) Trifolium-t. ; Pasture or roadside, from spring to early winter. B. Weed community-types in the border of cultivated field, abandoned cultivated field, afforested land and habitats of the communities type and their most luxuriant season. (1) Ixeris-type ; Barren soil, from spring to autumn. (2) Erigeron canadensis-t. ; Abandoned field, from summer to autumn. (3) Rumex Acetosella-t.; Acid soil, from spring to autumn. (4) Erigeron annuus-t. ; Abandoned field, from summer to autumn. (5) Oenothera biennis-t. ; Abandoned field, sunny place, summer. (6) Gramineae-t. ; Abandoned field, Garden, Roadside. Main species ; Agrostis palustris, A. stolonifera, Festuca elatior, Agropyron repens, Poa pratensis, P. sphondylodes, P. annua, Zoisia japonica, Anthoxanthum odoratum etc. (7) Epilobium angustifolium-t. ; New reclaimed land, sunny place, summer. (8) Taraxacum-t. ; Garden, Pasture, Ridge between rice-fields, Spring. Main species; Taraxacum officinale, T. hondoense. (9) Hydrocotyle ramiflora-t.; Border of cultivated field, slightly wet, Footpaths between rice fields, from summer to early winter. (10) Polygonum Thunbergii-t. ; Border of irrigation ditch, Autumn. (11) Plantago lanceolata-t. ; Pasture, Roadside, Summer. (12) Artemisia montana-t. ; Afforested land, Field, from spring to summer. (13) Eupatorium montana-t. ; Afforested land, Field, summer. (14) Petasites japonicus var. giganteus-t. ; Border of arable lands, Plains, Riverside, from spring to summer. (15) Miscanthus sinensis-t. ; Hill and plateau, Sunny place, from summer to autumn. (16) Pteridium-t. ; Fertile hills, Sunny place, Summer. (17) Rudbeckia-t. ; Slightly wet land in the border of cultivated field, roadside and railroad side, from early summer to late autumn. (18) Polygonum sachalinense-t. ; Border of arable lands, Riverside, fields and mountains, Summer. (19) Sasa-t. ; This is the commonest type in fields and mountains in Hokkaido. 3. As described above, the secondary succession of the weed community which grows on the new reclaimed land and on the abandoned field, changes almost in the order as follows. A. The succession of new reclaimed lands. Epilobium angustifolium-Erigeron canadensis-Oenothera biennis-type (1〜3 years)→Eupatorium montana-Sasa-Oenothera-type (3〜8 years)→Sasa-Pteridium-Larix-type (8〜13 years)→Larix-Sas
The reproduction curve is one of the most important attributes of an animal population, Some considerations were made on the types of the reproduction curve which is modified by several attributes of the population in their combination, using the data obtained experimentally in the populations of Lucilia cuprina (Fig. 2 NICHOLSON 1950), of Ephestia cautella (Fig.3,TAKAHASHI 1956a) and of Calandra oryzae(Fig. 4,UTIDA 1956)with reference to some attributes of them. The reproduction curve of mountain type observed on the Lucilia population may be one of the two extreme types and that of saturation type observed on the Calandra population may be another one. The type of reproduction curve of a given population is interchangeable between two extreme types as shown in Table 1 by some attributes being specific to the population and by a given condition, which modifies the operating mode of the population attributes.
Oshima Island having an area (10 km^2) is situated 50 km off the southwestern corner of Hokkaido. It is composed of the recent triplo volcano and the highest point attains 706 m. The vegetation showes fiesh and mostly unstable and some part is yet bare. The moss communities are well developed on the lava-flows as well as the slope of the volcanic ash and gravel. The Cares flavocuspis community sometimes associated with Aquilegia japonica succeed the former one. According to the deposits of the soil, Arunous sylvester and Maianthemum dila-tatum invade. Often they form the nisular carpet. Or such special slope as not influenced by the NW wind in the winter, the Cirsium kamtachaticum-Angelica ursima and Angelica ursima-Mis-canthus sinensis communities are formed. Berberis amurensis var. japoniea and Sambucus Sieboldiana var. Miquelii communities occur and form thickets in the special localities. The results of the ecological study of the experimental plots prove the communities-Moss, Monocotyle-donous sedge and grass, Dicotyledonous herbs, tall herbs and shruba and developmental states of the volcano. This is excelleat examples of the succession of the plant-covers of the recent volcanoes in Japan.
As a preliminary report of the comprehensive studies on the ethology of the Eastern Great Reed Warbler, the present paper deals mainly with the; life-history of a polygyneous family to illustrate its extreme polygyny and the fact that, in spite of this peculiarity, the breeding activity of this family represents fairly well the general seasonal trend of the species near Sapporo. Since the arrival of the male on May 23,1956 to the last record of fledglings on Aug. 20,the area shown in Fig. 1,was occupied by a polygyneous family, which consisted of 1 male and 5 females. Because of the sedentary nature characteristic of the species, the majority of various activities of these individuals was performed inside the area as summarized in Figs. 1 and 2. All the females except IV successfully reared their offspring. No remarkable relation was found among the females except for the attack of others by the nest owner when they approached too near to the nest area. The male participated neither in the nest building, nor in any practical sense, in the feeding. His role was directed mostly to the defense of the area against other conspecific individuals and cuckoos. The persistent attempt of one strange male to intrude into the area was traced and illustrated in Fig. 3. Furthermore, some considerations were given with respect to the occurrence of polygyny in this species.
1) From May 1948 to April 1949,the author investigated monthly the changes in the standing crop and the productivity of the population of Semisulcospira libertinus (GOULD) and Viviparus histricus (GOULD) on the coast of Lake Suwa near the inlet of the Rokuto River. Samplings were made at six stations at the depths of 20,40,60,80,100 and 130 cm. At each station collections were made ten times by the EKMAN BIRGB bottom sampler (1/50sq. m) to calculate the individual number and the dry weight of the soft body. 2) The number of adults increased in summer (Semisulcospira) and in autumn (Viviparus), and the young (less than 6-7 mm in diameter in Semisulcospira, and 11-12 mm in Viviparus) increased in spring. Adults. hibernated from November to April when the water temperature was lower than 10℃. The population numbers of Semisulcospira were 2-3 times more than those of Viviparus. 3) Dry weight of the soft part was calculated from the diameter of the shell by using the graph (Fig. 2) and added up monthly. The standing crops per unit area of Semisulcospira were 1-3 times larger than Viviparus. The former showed two maxima in June and October and two minima in midsummer and winter, and the latter showed a maximum in October and a minimum in winter. In both species the total weight of adults were far freater than those of the young. 4) Computation of productivity was made in the following way : Net increase of the standing crop was computed as the difference of two successive crops. The amount of decomposition plus perdation was taken as the difference between the potantial productions calculated from a formula (y=y_0e^q^t) and the actual standing crop of the next month, and the amount of respitation was estimated by respection the rate of respiration. The amount of gross assimilation was estimated as the total sums of these values. 5) Production of snails raised in summer with increased respiration and decomposition, resulting in the decreased net increase of the standing crop, and in autumn and spring this was just the reverse. No marked production was seen in winter. The plus values of net increases occurred only in autumn when the loss by decomposition and predation was very small. The total sum of net increases during a year except winter is nearly zero.
A horizontal, well sun-shiny area of 16×20 sq. m. in the precincts of a temple, deeply surrounded by trees and shrubs, inhabited by four species of ants-Camponotus herculeanus japonicus MAYR (abbreviated to C), Formica fusca japonica MOTSCHULSKY (abbr. to F), Aphae-nogaster famelica SMITH (abbr. to A) and Tetramorium caespitum jacoti WHEELER (abbr. to T)-was adopted as the observation ground. It was sectioned into a net of 2 m (partly 1 m)meshes and was baited at all corners of the meshes with such small insects as house flies and the like. All the baits were numbered by means of a tiny label respectively which was attached with a silk thread, in order to make clear their original positions even when they were carried afar by the ant. They were always replaced by another new ones as soon as dragged off. Observations were made as to the species and the nest of the ant by which the bait was found and transported. Also every event occurred during the transportation was recorded in detail. The investigation was conducted during 8-10 o'clock a.m. every day from Aug. 3 to 26,1956. The records thus obtained were put in order on a sheet of section paper per species (Figs. 2,4 and 5) and the foraging range of each nest population, its size, form and distribution, as well as its intra-and interspecific relations were investigated. Also the social order among the species concerned could be elucidated through the observation of their behaviour during forage and bait transportation. The results can be summarized as follows : 1) Habitat segregation and territoriality can be observed, as a rule, among nest populations of the same species (Fig. 2,4 and 5). Such relations, however, could not be confirmed, as a rule, between populations of different species, although there can be admitted some tendency towards such a segregation between A and T, A and F and C and A. 2) Foraging distance is greatest in F, next to it in C and much less in A and T, the last mentioned two being nearly equal to each other in the range of their foraging. (Fig. 3). 3) Social order among the species concluded from the observation of the behaviour at the time when they met with one another is A=T>C>F. While the ratio of the total number of the baits carried away by each species is C>T>F>A. However, when the dimension of the ants is taken into consideration, it comes to be efficiently T>F>C>A. Possibly this is the practical scale of the population prosperity among them.