The impacts of introduced poeciliid fish and Odonata on the endemic Megalagrion (Odonata) damselflies of Oahu Island, Hawaii.
This study, conducted in 1992-98, documents the presence of remnant Megalagrion populations in Oahu streams, wetlands and estuaries, and records the elevational distributions of fish (Poecilia mexicana, Xiphophorus hellerii, Gambusia affinis, P. reticulata and Sarotherodon melanotheron) introduced for biological control in each waterbody surveyed. The distributions of introduced Odonata are also recorded, because the 7 species of damselflies and dragonflies introduced to Oahu since 1936 present another potential threat to native Hawaiian damselflies. Native damselfly and introduced poeciliid fish distributions were mutually exclusive on Oahu, and it is concluded that this is probably due to predation by the introduced fish. By contrast, even the rarest native Megalagrion damselflies were found in areas containing introduced damselflies and dragonflies.