The effects of trampling and burrowing by streaked shearwaters were studied on the Persea thunbergii forest in Kanmurijima Is. The vegetation data were analysed using both the phytosociological tabulation method and principal component analysis (PCA). The vegetation ordination on the first axis reflected the environmental gradient from light to heavy disturbance by the streaked shearwater, and the vegetation ordination on the second axis represented the gradient from the latter phase of forest succession to retrogressive succession. The position of the three vegetation groups in the ordination diagram successfully explained the relation between the habitat and the species composition. The disturbance caused by activities of the streaked shearwater such as burrowing and trampling causes a decrease of species, especially character species of Camellietea japonicae, and also causes retrogressive succession: patches of Mallotus japonicus develop and many heliophytes occur.

To quantify the morphological and population responses of plants to grazing by deer, we conducted two deer-exclusion experiments in Nara Park, western Japan. The first experiment assessed the morphological differences in 10 traits of two species with erect growth (Oxalis corymbosa and Cyperus brevifolius. var. leiolepis) and two species with prostrate growth (Oxalis corniculata and Hydrocotyle maritima) between shoots inside and outside of the exclosures at the end of a growing season (late autumn). The size and weight of the leaves, stems and reproductive organs of the four perennials were significantly smaller outside the exclosures. The degree of size reduction was highest for an erect species, O. corymbosa, compared with the other three species, and was similar between the two prostrate species. The second experiment, using 11 erect species and 15 prostrate species, demonstrated that erect species exhibited greater reduction in leaf length and cover in the grazing environments compared with prostrate species, suggesting that the erect species suffered more from grazing. In conclusion, many of the plant species reduced their size under grazing pressure during the growing season, but the nature of the changes depended on the growth form of each species. It remains unclear whether the morphological reduction was an adaptive response to grazing.

In plants, negative reproductive interaction among closely related species (i.e., reproductive interference) is known to hamper the coexistence of congeneric species while facilitation can increase species persistence. Since reproductive interference in plants may occur through interspecific pollination, the effective range of reproductive interference may reflects the spatial range of interspecific pollination. Therefore, we hypothesized that the coexistence of congeners on a small spatial scale would be less likely to occur by chance but that such coexistence would be likely to occur on a scale larger than interspecific pollination frequently occur. In the present study, we tested this hypothesis using spatially explicit woody plant survey data. Contrary to our prediction, congeneric tree species often coexisted at the finest spatial scale and significant exclusive distribution was not detected. Our results suggest that cooccurrence of congeneric tree species is not structured by reproductive interference, and they indicate the need for further research to explore the factors that mitigate the effects of reproductive interference.

We investigated the range expansion histories of Machilus thunbergii populations in the Kinki region of central Japan on the basis of nuclear microsatellite data. In the Kinki region, M. thunbergii is typically found in the coastal area, with some fragmented populations inland, around Lake Biwa. Phylogenetic and Bayesian clustering analysis (STRUCTURE analysis) revealed that the inland populations have different genetic components between the west and east sides of Lake Biwa. The population located on the north side of the lake has an admixture of the two genetically differentiated lineages, contributing to an increase in the genetic diversity of the population. Populations around Lake Biwa had lost rare alleles and the F value obtained from STRUCTURE analysis was lower in the coastal populations than in the lake populations. These results suggest that populations around Lake Biwa experienced a bottleneck due to a founder effect during the initial migration to the lake and that glacial refugia of M. thunbergii in the Kinki region existed along the coast.

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