Using an index of relative importance (IRI), we studied the feeding habits of non-indigenous largemouth bass, Micropterus salmoides, in two lakes, Lake Saiko and Lake Shojiko, Yamanashi Prefecture, Central Japan. In Lake Saiko (n = 64), fishes, particularly a species of goby (Tridentiger brevispinis), were the main prey of bass (%IRI = 77.6%). In Lake Shojiko (n = 134), bass predated both fishes (%IRI = 46.6%) and crustaceans (%IRI = 49.5%), and the main prey species were another goby (Rhinogobius spp.) and a prawn (Macrobrachium nipponense). It appears that bass prey on any species that are available. Furthermore, prey selection differed according to the body size of the bass in one lake, but not in the other. In Lake Shojiko, individuals with a body length (BL) greater than 200 mm mainly predated crustaceans, whereas bass with a BL less than 200 mm mainly consumed fishes. In contrast, regardless of their body size, bass in Lake Saiko mainly preyed on fish. It appears that food selection by bass in these two lakes, which are in close proximity, is related to the availability and size distribution of the main prey species.

In this study, we attempted to evaluate the impacts of an introduced North American fish, the mosquitofish (Gambusia affinis), on populations of medaka (Orizias latipes), a native fish of Japan that is a red databook species. We estimated fish population densities and evaluated microhabitats in small irrigation ditches at 20 sites in Aichi Prefecture, central Japan. Mosquitofish and medaka were found together at 12 of these sites. The densities of mosquitofish and medaka were 9 m^-2 and 5 m^-2, respectively; the difference between these two densities was not statistically significant. However, medaka individuals in sympatry with mosquitofish had injured caudal fins and the severity of the injuries was correlated to the density of mosquitofish; this figure was statistically significant. Despite this, the density of the medaka populations was not explained by any of the microhabitat variables measured or by the density of mosquitofish. Based on the circumstantial evidence, we speculate that effects of interference competition by mosquitofish on medaka on the population level were limited; it is more likely that structural changes to paddy fields, including loss of habitat connectivity via irrigation ditches, contributed to determining the density of medaka.

Neolucanus insulicola donan, is a stag beetle endemic to Yonaguni Island, a small island in the Ryukyu Archipelago of Japan. The species is known to be a valuable indicator of the unique biogeographical composition of the archipelago and is useful for taxonomic research. However, it is now feared that this stag beetle is facing extinction as a result of the activities of insect dealers and collectors. Specimens are traded for high prices and are a rare commodity on the Japanese insect market. The species' population size was originally estimated to be over 600 but has declined to less than 1% of this number. In order to catch the larvae, the worst collectors have destroyed the tree cavities that the beetle uses for nesting. Collecting damages the habitat and this is likely to cause extinction of the species. It is obvious that such overexploitation has harmed the forest ecosystem on this island. Protection of this beetle depends on a prohibition on collecting and on preservation of Yonaguni Island's natural forest.

The wild boar (Sus scrofa leucomystax) population in Chiba prefecture, Japan, went extinct in the 1970's, subsequently recovering since 1986. To investigate genetic differences between this extinct population and contemporary wild boar populations in Chiba, we analyzed mitochondrial DNA (mtDNA) from wild boar specimens from the 1940s and 50s and contemporary animals. We successfully sequenced 572 base pair (bp) fragments of the mtDNA control region from three of four bones from extinct boars, and from 18 samples from contemporary wild boars. In the remaining of the four bones from the extinct population, only 385 bp of the 572 bp fragment were successfully sequenced. All specimens from the 1940s and 50s had haplotype J8, whereas contemporary boars had J3 and J10. Our findings indicated that the haplotype composition of the extinct boars was different from that of the modern population. Haplotype composition differences are not likely to be caused by migrations from neighboring prefectures to Chiba, because the current Chiba population is isolated from other populations. The contemporary population of wild boars in Chiba may have originated from escapes and/or introductions of feral boars or Inobuta from breeding farms.