Seed set of the invasive alien aquatic plant Gymnocoronis spilanthoides DC. was confirmed for the first time in Japan. In the Akuta River, Osaka Prefecture, flowering commenced in June and continued through December, and seed set was observed from July to October. A laboratory experiment using a gradually increasing and decreasing temperature method suggested that the seeds showed no dormancy and germinated between 15 and 35℃. While seed germination was promoted under light conditions, some seeds also germinated in darkness. Under field conditions, seed germination occurred under water as well as below ground. Since the seeds are winter hardy, overwintering by the seeds may allow this species to expand its distribution to northern regions, where the vegetative plant fragments die in winter.

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Verbena brasiliensis Veil. (Verbenaceae), an alien perennial herb native to South America, has spread rapidly in riparian habitats of Japan. To provide a scientific basis for assessing the impact of this plant on riparian ecosystems, we examined its phenology, growth and reproductive traits, seed germination, and its relationships to other plant species on a floodplain of the Ohtagawa River, Hiroshima Prefecture, Japan. This species has spread vegetatively by sprouting new shoots and forming adventitious roots from old, inclined stems. Stems that had inclined as a result of flooding were able to rapidly regenerate new shoots and flower. The seeds were found to require some light for germination, and the seed bank contained numerous viable seeds. After the autumn floods, several seedlings were observed under mature V. brasiliensis. In the laboratory, the powdered leaves of this species suppressed the growth of lettuce seedlings, suggesting allelopathy. Our data suggest that V. brasiliensis has a high potential for spreading and dominating riparian habitats. Further field research and an early strategy for successful control are needed.

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We analyzed the long-term changes in the spatial distribution of seagrasses in a seagrass bed on the Futtsu tidal flat in Tokyo Bay, Japan, based on remote sensing and geographic information system techniques using aerial photographs taken over 36 years. Comparisons with a field census revealed that the seagrass distribution could be estimated from the aerial photographs with an accuracy of 70%, although the distribution of three species (Zostera marina, Z. caulescens, and Z. japonica) could not be discerned. The seagrass bed extended a great distance offshore in the 1970s, reaching a maximum of 1.79km^2 in 1986. After that time, the area fluctuated and decreased to a minimum of 0.60km^2 in 2001. Temporal changes in the seagrass area did not correlate to changes in water quality, whereas retreat of offshore borders of the seagrass bed corresponded well with fluctuations in the location of sandbars. Thus, the long-term spatial dynamics of the seagrass bed in the exposed Futtsu tidal flat is strongly influenced by physical processes. Analyses of temporal changes in the seagrass area at a finer spatial scale revealed different patterns of fluctuation among subdivided parts of the seagrass bed, suggesting that factors causing temporal fluctuation vary among positions within the bed. The magnitude of temporal variation in each subdivision was larger than that of the whole seagrass bed, and asynchronous changes in each subdivision contributed to its overall stability.

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We investigated the river environment in the Shiretoko Peninsula, Hokkaido Island, Japan, with regard to the construction of dams. We listed the dams, including check dams, low ground sills, and similar facilities that might obstruct fish migration. More than 330 dams had been built in the peninsula region as of March 2003; 42.9% of the rivers had dams. Most of the dams were check dams designed to prevent disasters caused by debris flow, landslides, and floods, and none of the dams were primarily intended for irrigation or water intake. The number of dams per river depended on watershed topography and land use. Some rivers had many dams. The first dams were built in the early 1960s, and dam construction peaked in the 1980s, when an average of 10.5 dams per year were built. Although the rate of construction of new dams has declined, it has still exceeded seven dams per year since 2000. Generally, fishways have not been maintained properly and the conservation of fish habitat in the rivers is inadequate and insufficient.

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The species diversity of macrophytic flora in irrigation ponds located in the East-Harima area of Hyogo Prefecture, western Japan, has markedly declined over the past 20 years. In this study, we attempted to predict future changes in the macrophytic flora, using Markov chain analysis. Macrophytic vegetation in the irrigation ponds was first classified by cluster analysis based on vegetation data from a total of 831 irrigation ponds. We identified 17 vegetation types (Types 1-17) that were characterized by a few dominant species. We then used Markov chain analysis to calculate the future appearance (%) of all vegetation types from a matrix of transition probabilities of 165 irrigation ponds between 1980 and 2000. If changes similar to those of the past 20 years continue to occur, many vegetation types will disappear or be faced with extinction in the next 100 years. There is a strong probability that Type 1 (irrigation ponds without vegetation), Type 2 (dominated by Trapa), Type 3 (no single dominant species but Trapa occurs frequently), and Type 15 (dominated by Brasenia schreberi) will remain in the East-Harima area. This prediction reveals that many aquatic macrophytes in the East-Harima area may face extinction.

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Habitat fragmentation is one of the greatest threats to biological diversity. Here, I review the demographic and genetic consequences of habitat fragmentation for plant populations. Many empirical studies over the past 15 years suggest that seed production is markedly reduced with fragmentation, and that edge effects affect many fitness components, such as seedling recruitment and herbivory. In addition, fragmentation is often associated with reduced genetic diversity and elevated inbreeding, reducing offspring performance. These effects are expected to limit fecundity of remnant populations, although the consequences for long-term viability are not always apparent, particularly for long-lived species. Although several demographic studies have demonstrated that smaller populations are more likely to become extinct, the causes of extinction usually remain unknown. We still lack long-term demographic data to examine whether and how habitat fragmentation limits population growth of remnant populations.

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I investigated the parasites of alien terrestrial vertebrates occurring within the Japanese islands because the alien helminth species derived from introduced hosts may pose a pathogenic threat to humans and livestock. Moreover, these parasites may be able to switch hosts and deleteriously affect those native host-parasite relationships that have evolved due to adaptive radiation or co-speciation between native vertebrates and helminths. The patterns of host-parasite associations are generalized into four types: alien hosts and alien helminths, such as between Trachemys scripta and Falcaustra sp. (Nematoda); alien hosts and native helminths, such as between Rattus rattus and Heligmosomoides kurilensis (Nematoda), shifted from Apodemus speciosus; native hosts and alien helminths, such as between Cervus nippon and Nematodirus helvetianus (Nematoda), shifted from Bos taurus; and native hosts and native helminths, such as between C. nippon and Spiculopteragia houdemeri (Nematoda). The aberrant host-parasite relationships due to the presence of alien hosts and/or helminths comprise the first, second, and third groups. These relationships should be distinguished from native host-parasite relationships within the natural ecosystems of Japan, and potential strategies, including monitoring surveys, for reducing the pathogenic risk from these aberrant relationships are discussed.

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Estimating the size of sika deer (Cervus nippon) populations using fecal-pellet counts requires measurements of pellet density and defecation, pellet production and pellet decay rates. Although the latter three parameters vary with locality and season, parameters from one study are often used in other studies to minimize logistical costs. To obtain a more reliable size estimate of the deer population on the Ohdaigahara Subalpine Plateau in Japan, we assessed the number of pellets produced per defecation and the pellet decay rate in three types of vegetation (primary forest, Sasa nipponica grassland, and a transition area between these two types) from May to November 2001. We counted newly dropped pellets in quadrats in the primary forest and grassland every month. We estimated deer populations in the forest and grassland on the basis of these values in conjunction with defecation rates obtained from other studies. In addition, we examined the relationships between pellet decay rates and three variables: temperature, rainfall, and dung-beetle biomass. We found that pellet decay rates differed according to vegetation and season but were independent of temperature, rainfall, and dung-beetle biomass. As compared to estimates obtained using block count methods in other studies, the deer densities estimated by fecal-pellet counting in this study were considered overestimated, and varied with vegetation and season. On the basis of our results, we discuss the problems of estimating the size of deer populations using pellet counts and propose a procedure for a deer census that is suited to population management on the Ohdaigahara Subalpine Plateau.

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The effects of deer fences were monitored in secondary Quercus serrata forests in Nanko, Hyogo Prefecture, Japan. Although a large population of Erythronium japonicum occurred in this area during the 1970s, it had decreased substantially prior to this investigation. Following our experiment, the number of E. japonicum plants and their leaf lengths increased in the fenced plot, whereas both decreased in the unfenced control plot. No flowering individuals were observed prior to installing the fence, but beginning in the third year after the fence was erected, the number of flowering individuals increased annually in the fenced plot. Therefore, we suggest that deer fences provide effective protection for E. japonicum populations, which are currently declining because of browsing by sika deer (Cervus nippon).

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We discuss different perspectives relating to stream-environment conservation on the Shiretoko Peninsula, Japan, given the large number of dams in this area. Over 330 dams have been installed on this peninsula, of which most are check dams. Many species of Salmonidae, which are the primary fish of this peninsula, are anadromous. Dams have narrowed fish habitats in streams by blocking their migration routes, which could also have a devastating impact on terrestrial ecosystems. One reason for the large number of check dams in this area is that housing developments are concentrated on narrow flat areas, which are hazardous with regard to debris flows and flooding. This has undermined the conservation of stream environments. Information on the distribution of residential developments and infrastructure is required for rehabilitation and conservation of the stream environments on the peninsula; in addition, data on the characteristics of the natural environment must be collected and organized. The prevention of disasters caused by debris flows must be reconsidered, including a review of dams and land use based on the above information. Fishways are not a sufficient solution. It is important to develop novel ways to control debris flows and to facilitate fish passages that will avoid the complete blockage of entire channel sections.

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