Population structure of the damselfly Calopteryx japonica Selys in an isolated small habitat in a cool temperate zone of Japan (Zygoptera: Calopterygidae)

The population structure was studied in a small stream in a cool temperate zone of Japan in 1989 and 1990, using a mark-release-recapture method. The estimated daily number of males was 500 (1989) and 150(1990), while that of females was 450 (1989) and 100 (1990). The operational sex ratio in each year was probably unity. The daily estimate number of immigrants in each year was ca. 10% of the population, and the daily survival rate was more than 80%. Therefore, the populations in both years were considered to be closed. The distribution of each individual perching was surveyed. The perching site of the damselfly depended upon the sunlit area on the bank of the stream. Accordingly, they concentrated on the west bank during the morning, and the east bank during the afternoon. However, along the bank the perching sites of males was shown to be a regular distribution, due to territorial behaviour. There were many small insects that could be prey for the damselflies along the stream and the edge of the paddy fields nearby. Dipteran insects were dominant potential prey in this habitat. Since the habitat of the damselfly is surrounded by paddy fields and lakes, the maintenance of the population probably depends upon the abundance of substrate for oviposition and the larval habitat.