Spatial distribution and species composition of larval Odonata in the artificial reed community established as a habitat for Mortonagrion hirosei Asahina (Zygoptera: Coenagrionidae)

Yearly changes in the odonate larval community were surveyed for 4 yr after setting up an artificial reed community adjacent to the original habitat of Mortonagrion hirosei, an endangered brackish water sp. Only M. hirosei larvae were found in the original habitat during the survey period. In the first yr of the established habitat, Ischnura senegalensis was the dominant sp. in the larval community. Although the abundance of M. hirosei larvae increased year by year, becoming the most abundant sp. after the second year, the species composition of the larval community of the established habitat was different between the West and East because of environmental factors, such as saline concentration and reed shoot density. M. hirosei larvae had expanded their distribution to the entire area of the established habitat in 2005, while the distribution of I. senegalensis had been restricted to several patchy areas in accordance with a decrease in their population. There was a negative relationship between the number of M. hirosei and I. senegalensis larvae. The prey-predator relationship and competitive relationship between the 2 spp. should have affected the population dynamics and distribution of M. hirosei. The odonate larval community and habitat environment that is optimal for M. hirosei conservation are discussed from the viewpoint of both biotic and abiotic factors.