The freshwater insects of Australasia and their affinities
Abstract Stream faunas of New Zealand, southeastern Australia and Tasmania are characterized by numerous cool-adapted species of Ephemeroptera, Trichoptera, Plecoptera, Mecoptera and Diptera with southern (austral) affinities. They include a number of amphinotic (= circum-Antarctic) groups with close relatives in South America and their distributions seem best explained in terms of vicariance of an ancestral, Gondwanaland fauna. A second major component of the Australasian freshwater insect fauna has strong Oriental affinities and is thought to represent a more recent element which entered New Guinea, Australia, New Zealand and islands to the east in the last 20 million years. Included in this element are Trichoptera and Diptera with stream-dwelling larvae and Hemiptera, Coleoptera, Diptera and Odonata which mainly occur in standing waters. Mountains and islands formed when the Australian and Asian plates met in the late Cenozoic would have provided dispersal pathways for many of these groups. Colonisation of islands in the Pacific has resulted from early land connections, e.g. elements of the New Caledonian fauna, dispersal by air and most recently by man.