Effects of common carp on damselfly assemblages in rural reservoir ponds in Japan: Indirect effects mediated by aquatic plants

Abstract

To clarify the factors affecting damselfly assemblages in reservoir ponds, we surveyed the density of adults in 56 study ponds in rural areas of Iwate Prefecture, Japan, during 2008 to 2010. To compare the impact of indirect effects of common carp (Cyprinus carpio) with direct effects from environmental factors, we quantified indirect effects of common carp that were mediated by aquatic plants. For environmental factors, we examined the coverage of aquatic plants, the presence of marginal forests, the presence/absence of bullfrogs (Rana catesbeiana), forest dimensions, and pond density around each pond. Our results revealed that the presence of common carp had significant negative effects on the coverages of floating-leaved plants and submerged plants. In addition, the coverage of aquatic plants, which was defined as a function of carp occurrence, had significant positive effects on damselfly densities. This indicates that the introduction of common carp is the strongest operator in this region, modifying damselfly assemblages by reducing the local availability of aquatic plants.