Relationship between gross photosynthetic rate of Trapa natans L. leaves and light intensity was little influenced by temperatures ranging from 20℃ to 40℃. Seasonal changes in gross photosynthetic rate at light saturation were similar to those in biomass, with two peaks in the growing period and an abrupt decline in midsummer. Primary productivity during the growing period in 1979 of a.T. natans community in Lake Kasumigaura was estimated by gas exchange measurements and with a mathematical model. The estimated values for gross production, respiration and net production were 1168,501 and 667 g dry weight m^<-2>, respectively. The net production estimate agreed well with the estimate (606 g dry weight m^<-2>) obtained by the harvest method and was more than twice as large as the seasonal maximum biomass.
The number (S_n) and weight (Sw) of seeds produced by plants of successional dominants were studied. The relationships between S_n and plant height (H cm), diameter at stem base of plant (D cm) and their derivates (DH and D^2H) were described by the power function S_n=gX^n (X=D, H, DH or D^2H) for each species, except Miscanthus sinensis. The relationship between Sw and X was obtained by multiplying S_n by the seed weight of each species. The constants g and h in the equation of S_n=g (DH)^n were as follows : 4.76 and 1.69 for Polygonum persicaria, 1.38 and 1.78 for Chenopodium albunm (dominants of summer annual stage), 327.0 and 1.11 for Erigeron annuus, 706.3 and 1.11 for E. canadensis and 32.96 and 1.47 for Oenothera parviflora (dominants of winter annual stage), 1.21 and 2.02 for Artemisia princeps (dominant of perennial herb stage). The pioneer species produced a relatively small number of heavy seeds. Whereas dominants of the winter annual stage produced a vast number of light anemochore seeds. Total seed number m^<-2> produced by the stands were 144,222 for P. persicaria, 2,744,010 for E. annuus and 223,408 for A. princeps-Oe. parviflora. The weight of seed biomass to total biomass of the stands decreased from pioneer to final stages of succession of herbaceous communities. The seed production is discussed in relation to the type of life history of each species.
Anak Krakatau Island has been increasing in area and height due to repeated eruptions since its appearance on the sea in 1929. Its highest peak in 1981 was 199 m and a perrenial tall grass, Saccharum spontaneum L. was the most common plant on this island and grew very sparsely on the slopes of the cone. A dense grassland and a forest of Casuarina equisetifolia were found only on the east and north coasts. The occurrence of this grass decreases exponentially as the elevation increases, and no vegetation is seen above 120 m. Old aerial shoots and rhizomes of this grass were found buried in volcanic ash 60 cm deep even near the upper limit of its distribution. From the growing pattern of rhizomes it was determined that the grass had become established there during an inactive period of the volcano and that the rhizomes withstood repeated eruptions and the accumulation of volcanicash. Only a few seedlings were found in 1982.
Diatom assemblages of the sediments from two sites near Kutcharo Lake were analyzed to clarify the change in sedimentary environments caused by Holocene sea level fluctuation. Based on the ecological spectrum of the diatoms, the sedimentary history near Kutcharo Lake is inferred to have been as follows : (1) There were lowland peat bogs along the Okhotsk Sea coast. (2) The sediments of the lowermost Tr-1 zone were deposited on the littoral bottom of the paleo-Kutcharo Bay, which had been formed prior to 9,000 y.B.P. by the Holocene transgression. (3) Sedimentation in the MD-a subzone took place on the bottom of the neritic regions and in the MD-b subzone, and also on the bottom of the shore regions of the paleo-Kutcharo Bay. (4) The shore regions of the paleo-Kutcharo Bay changed directly into freshwater bogs during a regression from 6,000 to 5,000 y.B.P. (6) About 4,000 y.B.P., some ponds or small lakes developed in the bogs which had been formed at about 5,000 y.B.P. at two sites near Kutcharo Lake.
A new mathematical model for analyzing the mechanism of population growth of each of two kinds of plants in a field is proposed. Spatial structure of surviving plants, dispersion of seeds and the C-D effect were introduced into this model. As a result of simulations performed by using the model, the growth curves of the number of individuals and the total weight of the plants were obtained. According to the results, even a plant which is given unfavorable conditions for existence and germination can survive with another plant which is given favorable conditions for existence and germination by in creasing its number of seeds produced in a year or by lengthening its longevity.
The population dynamics in a whole process of regeneration was studied in a climax beech forest at Mt. Moriyoshi, Akita Prefecture, northeastern Japan. The change of biomass and the survivorship of beech in the process were clarified. Three phases were distinguished by the structure and the features of the regenerated populations in the process. In the initial 10 years or so, the density of the population was increased by the recruitment (phase I). After the population attained the full density state, the density decreased rapidly with the fast growth of trees (phase II). When the biomass of the population approached the maximum asymptote (within 70-80 years after the gap formation), the decrease of density slowed down (phase III). These three phases corresponded to the gap, building and mature phases, which were described by WATT (1947) and WHITMORE (1982).
The distributional pattern of crowns was analyzed by the coverage of crown covers (regarded as an elipse) and their center positions and compared with those of stems (standing positions) in several types of natural mixed forests (6 stands) of Hokkaido. The distributions of the crown-cover centers were uniform or random in upper layer trees, and all random in total trees (DBH&gnE5.0 cm). The crown cover distributions (based on coverage) in a lower layer were found to be more contagious than those in an upper layer, while the distributions of the stems were usually contagious ones. In the measuring of inter-layer distribution overlapping, the crown covers and their centers showed the same exclusive patterns between two of three layers, irrespective of the stem overlapping. These results reveal that trees survive by dividing their crown spaces in a level and escaping from the upper crowns. This simple structure was the main frame of the crowns' spatial distribution through the various types of natural mixed forests, and it had a scarce relationship with their stem distribution. The forming process of these patterns of crown distribution was discussed.
Observations were made of predation on Atlantic silversides, Menidia menidia, during their spawning runs in the intertidal zone of an estuary in South Carolina. Several fishes and avian predators captured M. menidia. Snowy egrets, Egretta thula, and Great egrets, Casmerodius albus, were the most dominant avian predators. We found specific differences in catch mode and actual predatory pressure for the two wading birds. Before the onset of spawning runs, Snowy egrets often made hovering catches which were inefficient, while Great egrets always made standing catches, striking at M. menidia from a standing position. Once a spawning run began, Snowy egrets ceased hovering and both Great and Snowy egrets frequently struck at fish from a standing position. Because of inefficiency in catching prey prior to a spawning run, Snowy egrets always remained unsatiated after a run had ended. A Great egret was satiated after consuming 114 fish (42% of its body weight) during a run. Intraspecific disturbances were often observed in both Snowy and Great egrets. Interspecific interaction did not present a serious problem to the subordinate species, Snowy egret.
In Mt. Taisetsu the forest limit was not dependent upon Kira's Warmth Index (WI) 15 but was controlled by either the prevailing wind or development of soillayer. The prevailing north-westerly wind in winter caused lowering of altitude of forest limit rather than WI15 altitude, possibly because it produced dehydrate-dessication damage in the winter buds of trees of the forest limit. Altitude of the forest limit was not necessarily related to the absolute altitudes of ridge but to the distance between the main ridge on a slope forming the forest limit and forest limit itself. Trees hardly grew in the boulder fields, which seemed to be formed by periglaciation activities in the palaeoclimatic conditions and contained a slight soil layer. The forest limit in the boulder fields descended lower than the level expected when a soil layer is present.
Post-metamorphic growth of the Japanese toad, Bufo japonicus japonicus, inhabiting the Botanical Gardens of Kanazawa University, was as follows : 1st year growth after metamorposis was about 50 mm (from 8 to 60 mm) in snout-vent length ; 2nd year growth was about 30 mm (60-90 mm) ; 3rd year growth was about 15 mm (90-105 mm) ; and from the 4th to the 9th year growth was only 1-2 mm per one year. Maximum sizes of males and females were 134 and 135 mm in snout-vent length, respectively. Most of the males reached sexual maturity in the spring of the 3rd or 4th year after metamorposis, but some of them began to breed in the 2nd year. Sexual maturity of most of the females was reached at the 4th or 5th year after metamorphosis.
Foraging strategies of a monophagous predator were investigated in the laboratory using a carabid beetle, P. perforata inhabiting colonial nest webs of S. imparilis. As hatchlings of this predator develop into 3rd instar larvae in the nest webs without moving among trees, it is essential that the predators effectively consume limited prey resources to maintain their own population, The functional responses of larvae showed what is called Holling's Type 2. Prey consumption in 3rd instar larvae was far more than in 1st and 2nd instar larvae. The predator larvae (1st, 2nd and 3rd instar) were able to feed on any kind of instar larvae of prey from the 1st to 4th larval stages. However, it was found that at some ages prey consumption was inadequate by analyzing the parameters of the disc equations. A small predator larva (1st instar) could not capture a large prey (4th instar) successfully and a large larva (3rd instar) could not gain enough food for growth when the prey was small (2nd instar). If adult predator females deposit eggs and 4th instar larval stages of S. imparilis, it is supposed that predator larvae feed on inadequate preys. However, in natural habitats there were no observations of such cases.