Biological diversity on semi-natural grassland resulting from the interactions between butterfly communities and plant communities

摘要

Although semi-natural grasslands make an important contribution to regional biological diversity in Japan, methods to estimate this contribution have not been investigated. To evaluate the biological diversity of semi-natural grasslands resulting from the combination of the three data sources—plant communities, butterfly communities, and the interaction of both communities—, three areas in the sub-alpine zone in central Japan were surveyed. The number of butterflies and the frequency of interactions with plants were recorded by the transect method within August and September 2002 at the same time when vegetation surveys were carried out. The biological diversity of a plant community as a semi-natural grassland in the Mt. Yashigamine was higher than that of the other areas examined, while the biological diversity of the Mt. Nyuugasa was higher than that of the Mt. Ikeyama (Mori and Okubo 2005). From the number of butterfly species and individuals and the characteristic species, Mt. Yashigamine was evaluated as having the highest biological diversity, with Mt. Nyuugasa second and Mt. Ikeyama third. From the results of the ER-index value analysis, the three study areas were similarly estimated to represent an environmental condition between the primitive stage and afforested stage. Nevertheless, the ER-index for the afforested stage at Mt. Ikeyama was the highest of the three areas, while the ER-index and Rl-index results from Mt. Ikeyama were lowest. The biological diversity of butterfly communities was the same as that of the plant communities. We postulate that the similarity in the two sets of results is because the plant communities influence the butterfly communities through the supply of feed and habitat. It appears that the Mt. Yashigamine scored the highest biological diversity because it occurs within a larger contiguous area of semi-natural grassland. The results of the frequency of nectar feeding at Mt. Yashigamine and Mt. Nyuugasa seemed to indicate a close interaction between butterfly communities and plant communities. But the interaction between the two communities did not seem to be very strong at Mt. Ikeyama. We suggest that the primary factor explaining this difference in results was the surrounding environment at each area. The results at Mt. Yashigamine and Mt. Nyuugasa were suggested that there is a close relationship between butterfly communities and plant communities. The combination of the three data sources—plant communities, butterfly communities, and the interaction of both communities—seemed to be a useful method of evaluating biological diversity. Nevertheless, to confirm this relationship, more detailed surveys and alternative analyses of the interaction between the two communities are required.