Identifying priority habitats and monitoring species for conservation and restoration of lentic Odonata habitats: assemblage nestedness on Amami-Oshima Island, Japan.
We investigated Odonata faunal and habitat characteristics (forest cover, emergent, submerged, floating-leaved and floating plant covers, pond area, NO3-, chemical oxygen demand, and presence/absence of a nonnative fish) in 10 ponds on Amami-Oshima Island. In total, 26 species of six odonate families were found, and we detected significant nestedness of species composition among the ponds (22 species in the most species-rich pond, and 8 species in the most species-poor pond). Species found only in the most species-rich ponds were: Anax nigrofasciatus nigrofasciatus, Acisoma panorpoides panorpoides, Agriocnemis famina oryzae, Rhyothemis severini, Anasiaeschna martini, Hemicordulia okinawaensis, Lyriothemis elegantissima, and Hydrobasileus croceus (hereafter referred to as the rare species). These rare species are generally known to preferentially inhabit ponds with lush emergent plants and/or to prefer cooler habitats shaded by forest cover, such as Anax nigrofasciatus nigrofasciatus, Anac. martini, He. okinawaensis, and L. elegantissima. In contrast, the common species also found in species-poor ponds were: Ischnura senegalensis, Pantala flavescens, Anax parthenope julis, Ictinogomphus pertinax, and Tramea verginia, which are known to prefer an open water surface as spawning habitat. These differences in habitat preference between the rare and common species may be among the major reasons for the significant positive effects of percent forest cover and emergent plants on Odonata species richness. These results suggest that nestedness helped identify precise habitat characteristics and rare species that should be considered for conservation and restoration of lentic habitats on Amami-Oshima Island.