論文

The objectie of this study is to propose a method for evaluating ecological network. We propose to consider two classes of spatial scales for evaluation. In the macro-scale research, we classified land use types by satellite data, and extracted two areas of heterogeneous or homogeneous land use in the object region In these areas, we performed micro-scale researches through field survey and geographical information based topographical maps. Throughout these researches of different spatial scales, we evaluated present ecological network and discussed the availability of this method.

主に列状の緑地と島状の緑地、周辺の土地利用に着目し、我が国の都市域において生態的ネットワークを構築する手法を確立するための基礎的な研究として、鳥類の分布との関係を明らかにすることを試みた。研究対象地は、兵庫県西宮市西部とした。2002年12月から 2003年２月の間に、夙川沿いの列状緑地、甲陽園一帯の島状緑地、北山公園において、ライントランセクト法による鳥類調査を行った。鳥類の確認地点を中心として半径50ｍのバッファーを発生させ、その種ごとの土地利用比率を分析した。その結果、主に樹林を利用する種にとっては、50％以上が樹林で占められていることが必要であることがわかった。また、いくつかの種によっては、低木層、草本層の存在が重要であることがわかった。最後に、都市域において鳥類を対象とした生態的ネットワークを構築する際の要点をまとめた。

都市近郊に残存する樹林地において,ダミーの卵を入れた人工巣を設置して卵が捕食される状況を調査し,樹林地における捕食圧の空間的なパターンを明らかにすることを試みた.調査は,東京都と埼玉県の境に位置する狭山丘陵の比較的大規模な樹林地とその周辺の孤立樹林地5ヵ所の計6ヵ所で行った.樹林地では,周囲から侵入してくる捕食者によって,林縁付近においては被捕食率が高くなることが予測されたが,林縁からの距離と被捕食率の間には統計的に有意な相関は認められなかった.また,面積の小さな樹林地では被捕食率が高いことが予測されたが,比較的大規模な樹林地でもっとも被捕食率が高く,その他の孤立樹林地と有意な差を示した.最も面積の小さい樹林地で捕食率は最低であった.生息密度の高さからハシブトガラスが主な巣の捕食者であると考えられるが,ハシブトガラスの密度は狭山丘陵の樹林地で最も高く,またハシブトガラスは樹林地周辺に限らず樹林地内部でも多数観察された.このことから,鳥類の巣における捕食は,主な捕食者の樹林地内外の分布状況によって大きな影響を受けていることが示唆される.

Agricultural reservoirs are now regarded as important habitats for some aquatic organisms, though their value as habitats of algae has clarified little. Diatom is often the most dominant component of freshwater algal communities and its contribution to species diversity can not be negligible. We studied periphytic diatom assemblages in 24 agricultural reservoirs in Awajishima Island, Japan to find major factors controlling diatom species composition. As it has often been reported and discussed, influence of eutrophication to species composition was detected. However, surrounding land cover was estimated to be the most important factor: some dystrophic or soil diatoms characterized diatom assemblages in reservoirs surrounded by woodland. Compositional difference caused by substrate was not detected. It is concluded that water quality management considering eutrophication and land use management where conservation priority is put on woodlands surrounding reservoirs are possible means to conserve diatom assemblages in agricultural reservoirs.

  Dragonfly and damselfly (Odonata) species were surveyed from May to October 2002 on 38 small irrigation ponds in the north part of Awaji Island. The investigation was conducted nine times on each pond. Totally 1568 individuals of 28 species were recorded for six months. We selected nine species recorded more than 40 individuals and analyzed the relationships of individual number of these species with environmental factors, including conductivity, NO2-, NO3-, NH4-, PO43-, COD, surrounding land uses within 50 meters from the edge of pond, the number of aquatic water plant species, and autocovariates explaining spatial autocorrelation, using Generalized Linear Models (GLM). The result showed that NO3-, COD, surrounding grassland, woodland and the number of water plant species were critical factors for the distribution of some Odonata species.

We digitized land uses in the latter Edo era in Awaji Island, central Japan, using old maps called Bugengunzu. Bugengunzu is one of the oldest map by a modern measurement method in Japan, which was drawn by Okazaki family working for the domain of Tokushima from 1802 to 1847. Two maps (approximately 1/18000) covered whole Awaji Island. A total area of woodland was 34,916 ha at that time. Compared with the area in 1980's, which was 34,729 ha, only 0.5 % of woodland disappeared in 150 years. Some woodlands changed into fields and plantations in 1960's in north and middle parts of the Island. On the other hand, some fields on the steep slop and at high altitude in south part were abandoned, then these areas changed into woodlands.

This survey monitored the quantity and distribution of egg clutches of Tohoku salamander (Hynobius lichenatus) in the tsunami inundated lowland area from the period 2012 to 2015, looking at the case of Moune district, Kesennuma city, Miyagi prefecture, Japan. After the 2011 Tohoku Earthquake, lowland area almost changed into wetlands by erosion and land subsidence, and seawater ran into a part of the lowland. Lots of egg clutches were found in the whole area in 2012. However several egg clutches deposited in brackish-water were dead. After 2013, the number of egg clutches declined, and the distribution moved inland. The number of egg clutches roughly increased in 2015, indicating the meta-population of Tohoku salamander's resilience against temporary disturbance caused by the tsunami. Models of relations analyzed between the numbers of egg clutches in each year showed larger population had higher resilience and the numbers of dead egg clutches had negative correlation to the total numbers of egg clutches in late years. Results indicated that the environmental changes after the tsunami had more severe impacts on the population's survival. However the population of Tohoku salamander had resilience under the natural state. This resilience may be weakened by man-made induced environmental changes and habitat loss from the tsunami recovery and reconstruction works. Hence, the need for conservation and monitoring was suggested.

ヨシ群落の効率的な生育管理を実現するため，広域的なモニタリング手法の開発が期待されている。 本研究は，中国向海(シャンハイ)湿地のヨシ群落を対象にし，現地調査データと衛星画像データの両方を使用し，ヨシの在・不在，草高，茎径，稈密度の四つの予測モデルを開発した。最適モデルの結果により, ヨシの生育に最も影響している指標は水分条件と傾斜角であることがわかった。この結果を踏まえて, 保全策を検討する基礎資料として, 2010年の向海湿地のヨシ群落の生育予測図を作成した。