To clarify the major factors affecting odonate assemblages in rural reservoir ponds among within-habitat environments, land use around ponds and spatial autocorrelation, we surveyed odonate adults (Zygoptera and Anisoptera) in 70 study ponds in Ibaraki Prefecture, Japan, during three sampling periods in 2005. Redundancy analyses (RDA) for these three factor groups were executed to determine their strength for explaining the odonate species composition. Their relative contributions were also evaluated by the method of variation partitioning.

Results/Conclusions

41 odonate species were recorded in the study ponds in total, and 24 of them, excluding rare species, were used for our analysis. Summed effects including all three factor groups explained approximately 39 % of the variation in odonate species composition. We found that spatial autocorrelation has the greatest importance, though the within-habitat environment and land use had comparable effects. We conclude that spatial autocorrelation should be considered in this type of analysis, though we could not clearly explain what made such a spatial structure. Pond area and debris that had accumulated at the bottom of ponds were selected as the within-habitat environment, and the forests and paddy fields around ponds were selected as the land use after the procedure of forward stepwise selection. These results suggest that the recent decrease of forests around the ponds has a negative effect on the odonate assemblages.