Relationships Between Browsing on Dwarf Bamboo (sasa Nipponica) by Sika Deer and the Structure of Ground Beetle (coleoptera: Carabidae) Assemblage

27 Mar Relationships Between Browsing on Dwarf Bamboo (sasa Nipponica) by Sika Deer and the Structure of Ground Beetle (coleoptera: Carabidae) Assemblage

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Abstract

ニホンジカによる森林衰退が進む奈良県大台ヶ原では, 防鹿柵によるシカの排除が行われているが, これが節足動物の多様性に与える影響は不明である。本研究では, ニホンジカによるミヤコザサの採食とオサムシ科甲虫の群集構造との関係を調べるため, シカの主要食物であるミヤコザサの現存量を防鹿柵や刈り取りにより操作した実験区を設け, ピットフォールトラップによる捕獲調査を行った。また, オサムシ科甲虫の食物となる地表性小動物を捕獲するため, 粘着トラップを各実験区に設置した。オサムシ科甲虫の総捕獲数, 種数と多様度指数はササ現存量と明確な関係がなかった。最優占種オオクロナガオサムシ捕獲数はササ現存量とバッタ目捕獲数に対して正の関係があった。2番目に多いフジタナガゴミムシは, ササ現存量との関係はなく, 開空度と負の関係があった。3番目に多いコガシラナガゴミムシ捕獲数はササ現存量と負の関係があり, トビムシ目, ハエ目, ハチ目と正の関係があった。これらの結果から, ニホンジカの採食によるミヤコザサの減少は, オサムシ科甲虫の多様度には大きな影響を与えないが, 群集構造には影響すると考えられた。

English Abstract

An overabundance of Sika deer (Cervus nippon) at Mt. Ôdaigahara, in west-central Japan has necessitated the introduction of exclusion fences to protect forest decline from excessive feeding damage. However, the effect of these exclusion fences on the biodiversity of arthropods within the protected areas has not been investigated. In this study we examined the relationships between the volume of dwarf bamboo (Sasa nipponica), the major forage for the deer, on associated with browsing by deer and the structure of ground beetle assemblage. Both inside and outside of the exclusion fences, pitfall traps were setup in plots that had been assigned treatments of either no treatment (control) or artificial clipping of dwarf bamboo. Ground sticky traps were also set up in each plot to sample the abundance of small animals as the diet of ground beetles. Bamboo volume did not reltate to abundance, species richness, or diversity of the ground beetle assemblage. The abundance of the most domi nt beetle species, Leptocarabus kumagaii, increased positively in response to both bamboo volume and the abundance of Orthopterans. The second most domi nt species, Pterostichus fujitai, did not relate to bamboo volume, but decreased in abundance in relative to the propotions of open canopy. The third most species, Pterostichus microcephalus, decreased in abundance relative to bamboo volume, but increased positively in response to the abundance of Collembolans, Dipterans, and Hymenopterans. These results suggested that reduction of bamboo volume by browsing of deer did not affect the diversity of ground beetle aseemblage but affected its structure.