Driven by diadromy: Its role in the historical and ecological biogeography of the New Zealand freshwater fish fauna

Abstract

More than half the New Zealand freshwater fish fauna is diadro‐mous, most of these species being amphidromous. Diadromy is a major determinant in many aspects of the historical and ecological biogeography of the fauna. These aspects include: 1) serving as a source of ancient to recent derivations through transoceanic dispersal of diadromous species, a process that continues today; 2) populating remote, oceanic islands in the New Zealand region; 3) maintaining fish populations on nearshore islands with ephemeral streams; 4) determining the overall ranges of species both within and beyond New Zealand; 5) providing a major contribution to species richness in river systems; 6) structuring of riverine fish communities; 7) facilitating recovery of communities after perturbation at recent and geological time scales. Overall, diadromy is seen as the single strongest determinant of the characteristics of the fauna. Principles that account for this contribution by diadromy to the nature of the fauna apply globally, to the extent that fish faunas in other parts of the world are diadromous.