Sexual differences in growth rate were examined in the freshwater prawn Macrobrachium nipponense, by rearing field-collected juveniles for more than two years. The mean body length of females was greater than that of males at the first breeding season, by when almost all females had attained sexual maturity. It was hard to explain the sexual difference in body size observed in the natural population (larger mature males than females) in terms of the difference in growth rate during the first year in captivity, and that was attributed to the different age structure of mature individuals, viz., older (two years or over) males than females. The presence of such older males in this species was noted as being unique among freshwater caridean prawns and shrimps, in which males are usually smaller than females and both sexes have an annual life span.
No territoriality nor dominance hierarchy was evident in the Japanese toad, Bufo japonicus japonicus. Newly metamorphosed toads searched for food actively during summer, whereas subadult and adult toads were inactive during this season. Young toads inhabited the vicinity of the breeding pond, but adult toads had a tendency to leave the pond and to establish their home ranges at the peripheral zone of the distribution area. Adult males and females mated during early spring, at which young toads were still present in their hibernation sites. These results seem to provide evidence for some isolating mechanisms between young and adult toad, for large toad sometimes eat small toad.
The life cycle of a grapsid crab Hemigrapsus penicillatus inhabiting the intertidal boulder shore was investigated in the Gamo Estuary over a two-year period using stone-filled basket traps. Ovigerous females occurred from June to September, with the maximum ratio to the total number of adults being present from August to September. Megalopae larvae settled intensively in September. It was estimated that only 0.17% of the eggs produced in the population developed as far as juveniles of 0.3 cm carapace width. By early December these had reached 0.6 cm width. Little further growth was evident until March, but by the following December individuals had reached 2.0 cm. Mature size was reached 10-11 months after settiement. Life table analysis of this population suggested a 2-year life span with two overlapping cohorts.
Many dynamic correlations exist between human activity and ecological systems. In the case of traditional slash and burn agriculture, many systematic techniques which work in harmony with ecological systems have accumulated during the long period of human history. To evaluate responsible methods of land use, the ecological basis of such knowledge and its implementation effects should be understood. From this viewpoint, the effects of burning on the germination of viable seeds were investigated at a slash and burn site in the temperate zone of Kyushu. Seeds responded to the burning in one of the following three ways. (1) Burning decreased seed germination of annual herbs of Compositae such as Erigeron sumatrensis, E. annuus and Crassocephalum crepidioides. Thus burning is useful for weed control. (2) Burning stimulated seed germination of woody species such as Rubus spp. and Rhus javanica. This contributes to decreasing the leaching of inorganic nutrients from soil and to the rapid recovery of vegetation during a fallow period. (3) Burning had no effect on seed germination of some perennial herbs such as Eupatorium chinense var. simplicifolium.
Although most alpine plant communities have standard flowering times, in the Southern Daisetsu Mountains the Primula cuneifolia-Potentilla matsumurae community blooms at different times at different locations. In this area, flowering of the Primula cuneifolia-Potentilla matsumurae community depends on the duration of snow cover, and usually occurs within about 10 days of snow melt. These two small herbaceous species can grow in the short period following snow melt when the soil is waterlogged, and on unstable surfaces affected by soil creep and/or frost action. Consequently, the Primula cuneifolia-Potentilla matsumurae community can occupy many situations under a greater variety of snow release conditions than other plant communities.
Pollen analyses were made on materials collected from the Hakkoda Mountains. Comparative studies made between these pollen diagrams and those of previous workers enabled the clarification of the vegetational history of the subalpine zone of this mountain range. Results show that 8500-4500 years B.P., the subalpine zone of this area was covered by meadow-like vegetation, and that between 4500-2500 years B.P. this was succeeded by a cover of subalpine deciduous scrub chiefly consisting of Quercus. The Abies mariesit forest began increasing in the subalpine zone about 3000 years ago, and has markedly extended its cover there during the last 1500 years.
Light attenuation within plant canopies and their photosynthetic production are reviewed on the basis of assumptions constructing MONSI-SAEKI'S theory. Emphasis is given to the relationship between light attenuation and canopy structure, and a comprehensive summary of relevant publications is given. A model developed from the MONSI-SAEKI model of canopy photosynthesis to give a more accurate estimate of photosynthetic production by forest canopies is introduced and its practical applications to forest stands are discussed.
Parental-care patterns of fishes are surveyed to examine their evolutionary courses and the factors influencing the care-taker's sex. The Agnatha are nonguarders, the Chondrichthyes are internal bearers (with internal fertilization), and in 99 (24%) out of 418 families of the Osteichthyes guarding, external bearing or internal bearing are exhibited in 69,21,and 24 families, respectively. Male care is the most common among guarders, but only females perform internal bearing. The care-taker's sex is believed to be determined primarily by the ancestral mating system and the method of care : 1. Because rates of gamete production are faster in males than in females, male mating territories will predominate among nonguarders. From ancestors of this mating system, guarding by males but bearing by females will evolve, because males can take care of multiple clutches by guarding but not by bearing. 2. A portion of external bearing is derived from guarding, and prolonged guarding after the end of internal bearing is rarely developed in fishes. The sexes of the secondary care-takers are usually the same as those of the ancestral ones, but are also influenced by the new methods of care and the ancestral mating systems. These and other predictions are examined in relation to current hypotheses.