Geomorphology, Development of Running Water Habitats, and Evolution of Black Flies on Polynesian Islands

Abstract

Running water habitats develop in concert with the age of hotspot volcanic islands. This study tracks the geologic and hydrologic processes involved in this development for the Society Islands, French Polynesia. Over a period of about 6 million years, these islands have rafted northwest on the Pacific Plate and eroded from high islands with many stream systems to atolls with no running water. Black flies that require running water for their immature stages have undergone a species radiation into a wide array of running water habitats on Tahiti. From there, black flies appear to have dispersed to older islands farther west. The reduction of running water habitat with the island's increasing age has had consequences for the biogeography of these insects. The habitat generalist species are the most widespread. Species with dependence on cascades cannot colonize islands where cascade habitats have eroded away.