At the beginning of this century, the swamp-eel Monopterus albus was introduced from Korea to an area of Nara Prefecture, located at or near one of the origins of the Kizu, Yamato and Yoshino River Systems. Our samplings were carried out between 1988 and 1997 and information offered by farmers was confirmed that the fish was distributed in the three river systems. Furthermore, a comparison between our results and previous reports clearly shows that the fish has expanded its distribution range. Closer surveys revealed that the fish did not occur at higher altitudes which were isolated from lowland fields providing a habitat for the fish, even though both area were cconnected by rivers. In contrast, it occured in paddy fields on both sides of passes which the fields traversed. The fish seems to be a poor swimmer because of its degenerate fins. These facts suggest that its wide distribution range is due to its high dispersal ability and some extrinsic factors as suggested below: 1) ability to breathe air, which enables it to leave bodies of water; 2) release at or near the origins of the three river systems; 3) abundance of contiguous paddy fields which are suitable habitats for the fish.
We investigated the feeding behavior and use as a lure of the first dorsal fin ray of the bothi flounder, Asterorhombus intermedius toward prey goby fish (Acentrogobius pflaumii, Favonigobius gymnauchen) in Kagoshima, Japan. The distal two thirds of the first dorsal fin ray of the flounder bears membranous flaps. In an aquarium with 1 or 2 prey fish, the flounder waved its first dorsal fin ray repeatedly around the mouth when a prey fish approached. The effect of amputating the first dorsal fin ray on attracting prey fish was then tested. The number of prey fish that approached decreased significantly after amputation. Thus the movement and morphology of the first dorsal fin ray of the flounder mimics an annelid worm or crustacean, and acts as a lure for prey fish.
Forest type selection by the Japanese squirrel, Sciurus lis TEMMINCK, was investigated in an area of fragmented vegetation near Mt. Takao, Tokyo. The radio-tracked 7 male and 6 female squirrels stayed in natural forests most frequently and in mixed-species forests second most frequently during both active day time and inactive night time. The squirrels spent less time in artificial coniferous and deciduous forests, except for walnut stands, a major foraging site, and avoided arboretum, shrub and grass.
Seedling emergence usually occurs asynchronously, spread over several weeks or months. In some species, two or more discrete cohorts emerge in different seasons of the year (e.g. in autumn and spring). Such phonological patterns may result from seed heteromorphism in relation to dormancy. The term heteromorphism was originally used with reference to morphological differences in seeds. However, it is now applied to physiological variation in dormancy characteristics, even without accompanying morphological dissimilarities (cryptic heteromorphism). The general tendency in heteromorphic plants is that dormant seeds are likely to be produced earlier and /or dispersed later than nondormant seeds. These patterns are closely related to the position of seeds within or between fruits in the same plant. Somatic heterochrony may well explain the evolution of seed heteromorphism. Three hypotheses are addressed in relation to the adaptive significance of seed heteromorphism: 1) risk spreading in a temporally variable environment, 2) avoidance of density-dependent mortality, and 3) escape from sibling competition. Although these are not mutually exclusive, risk spreading seems to be the most important, since the ratios of dormant: nondromant seeds vary with latitude or altitude depending on environmental harshness. Finally, I propose the idea that seed heteromorphism may have evolved even in perennial or iteroparious plants. I also point out that, in some cases, spreading germination over time could be realized even in species which do not show seed heteromorphism.
Patterns common to the early stages of old field succession in temperate regions, as well as the life history features of the dominant species, have been thoroughly studied, especially in the USA and Japan. Seed-bank summer annuals, e.g. Ambrosia artemisiifolia and Chenopodium album, dominated as pioneers in first-year old fields by virtue of germinating from their buried seed population in the spring following winter dormancy. Wind-dispersed winter annuals or biennials, e.g. Conyza sumatrensis and Erigeron canadensis, which easily invade and grow under the canopy of the summcr annual communities due to their shade-tolerant rosettes, dominated in the second-year old fields. These were gradually succeeded by perennial grassland species in the third year or later. On the other hand, wind-dispersed summer annuals, e.g. Erechtites hieracifolia and Crassocephalum crepidioides, dominated during the first year in disturbed mountainous sites of temperate regions, such as clear-felled forest or sites burned by forest fires. In shifting cultivation sites of tropical regions, the same types of wind-dispersed annuals, e.g.C. crepidioides, Ageratum conyzoides and Erechtites spp., dominated as pioneer weeds and were rapidly succeeded by pioneer shrub or tree species within a few years. Pioneer annuals that use a seed bank strategy, common to succession in temperate old fields, were not found at these sites, and thus the invasive strategies of the pioneer annuals of secondary succession in these regions apparently differ from these in old fields. Previously, causal analyses of the early herbaceous stages of secondary succession have been conducted primarlly in old fields of temperate regions, rather than in disturbed sites of temperate and tropical forest. Thus, the succcssional patterns and life history features of pioneer herbs in these areas require further study.