環境

本研究では典型的な都市河川である多摩川を対象に、草地性小動物であるネズミ類の種組成と草地状態（植生・土壌）を検討した。下流域でハツカネズミ、中流域でハツカネズミ、アカネズミ、カヤネズミの生息が確認された。河口部や一部の中流域の地点ではネズミ類の生息が確認されなかった。ハツカネズミとアカネズミの生息分布は中流域で境界が示され、両種の分布は河川敷の環境条件と共に、草地環境の連続性、地域の都市化等、周辺植生や土地利用等にも影響を受けている可能性が推察された。アカネズミの生息分布は河川敷内における植生の被覆と、周辺樹林地との連続性が関与している可能性が考えられ、今後はアカネズミの周年利用、移動能力の把握が研究課題となった。カヤネズミの営巣は中流域以上に限定され、営巣に必要な高茎草本群落の規模と共に、群落を構成する種組成にも影響を受けている可能性が示唆された。なお、既往文献で記録されているハタネズミの生息は確認できず、本種が生息可能な土壌条件や草地環境の変容等、河川敷の生態的な質の低下が懸念された。

This survey studies the species composition of mice, small grassland animal species, and the grassland conditions (vegetation and soil) of the Tama River, which is representative of urban rivers. Through the survey, it was confirmed that house mice inhabit the downstream, and that house mice, large Japanese field mice, and harvest mice inhabit the midstream. No mouse inhabitation could be confirmed at the estuary and some parts of the midstream area. The border of habitat distribution of house mice and large Japanese field mice is shown at the midstream area. The distribution of the two species is believed to have been affected by the environmental condition of the riverbed, continuity of the grassland environment, urbanization of the area, vegetation in the vicinity, land use, and so on. The distribution of large Japanese field mice is believed to be related to the continuity of vegetation covering the riverbed area and neighboring forests. The subjects of year-round use of large Japanese field mice and their mobility capability merit further research. The harvest mice only nest in areas in and above the midstream, showing that its distribution may be affected by the size of the tall herb communities necessary for nesting and the species composition of the herb communities. However, inhabitation of Japanese grass voles could not be confirmed, despite the fact that their existence was recorded in past literature. Possible deterioration in the ecological quality of the riverbed, such as changes in the soil condition and grassland environment of the habitat of this species, were considered

葉山嘉一（日本大学生物資源科学部植物資源科学科 准教授） 大澤啓志（日本大学生物資源科学部植物資源科学科 専任講師） 黒田貴綱（日本大学生物資源科学部富士自然教育センター 職員）

Kaichi Hayama (Associate Professor, Plant Science and Resources, College of Bioresource Sciences, Nihon University)
Hiroshi Osawa (Instructor, Plant Science and Resources, College of Bioresource Sciences, Nihon University)
Takatsuna Kuroda (Staff, Fuji Nature Education Center, College of Bioresource Sciences, Nihon University)