Factors Influencing the Distribution of Dragonflys (Odonata) in the Agricultural Landscape in Hokudan-cho, Hyogo Prefecture

Abstract

There is a huge number of small irrigation ponds in the agricultural landscape of the north of Awaji Island, Hyogo Prefecture. Recently, managements of many ponds have been abandoned. However, these ponds are used as habitat by many organisms. They have an important role to maintain biodiversity in this area.
Dragonfly (Odonata) species were surveyed in 24 irrigation ponds in Hokudan-cho, the north of Awaji Island. Thirty-seven species were catched and/or observed from June to September 2000. The number of dragonfly species had no relation with water body area of irrigation ponds. Twenty-four ponds were classified to five types by TWINSPAN (Two-way Indicator Species Analysis). The classification of TWINSPAN was analyzed by Classification and Regression Trees using explanatory variables about environmental factors of irrigation ponds. The results showed that altitude, neighboring woodlots, water body area and water quality influenced the component of dragonfly species. Especially, it was important for species preferring edge and/or inside of woodlot that over 45 percents of pond surroundings were adjacent to woodlots. It was also suggested that surrounding land uses influenced the distribution of dragonfly species.