Environmental Characteristics accounting for Odonate Assemblages in Rural Reservoir Ponds in Japan

Abstract

To clarify the effect of environmental factors on odonate assemblages in rural reservoir ponds, we surveyed the odonate adults (Zygoptera and Anisoptera) in 70 study ponds in Ibaraki Prefecture, Japan, during three sampling periods in 2005. Cluster analysis, indicator species analysis (INSPAN), and non-metric multidimensional scaling (NMDS) were used in combination to determine the relationship between odonate assemblages and environmental variables, i.e., biotic, physicochemical, and regional variables (the types of land use surrounding the ponds). A total of 41 odonate species were recorded in the study ponds, and 24 of them, excluding rare species, were used for each analysis. The study ponds were classified into six groups, and significant indicator species were selected from four of these groups. Examination of the correlation between each environmental variable and NMDS axes 1 and 2 revealed the profound effects of the presence of forest, paddy field, or open area around the ponds on the indicator species composition of each group. It was also revealed that the aquatic vegetation and forests around the ponds provide desirable conditions for the odonates and, in contrast, concrete revetment has a detrimental effect. These results suggest that the recent decrease of forests around ponds and the reconstruction with concrete revetment will have a negative effect on the odonate assemblages in ponds.