Dispersal versus vicariance, artifice rather than contest

The opposition between dispersal and vicariance is shown to be an artifact of poorly defined concepts. In place of a simplified opposition, five processes are identified that affect plant and animal distributions. These processes -modification, movement, mixing, splitting and juxtaposition – are not logically equivalent as they operate over different time scales. The time scales discussed are ecological time, geomorphological time, and geological time. Processes operating in geological time provide the context in which shorter time scale processes operate, and as such take logical priority. Dispersal as a process operating in ecological time is discussed in relation to the modification of the New Zealand avifauna by introduced species. Dispersal as a process operating over geomorphological time is discussed by reference to transitional biotas in Wallacea. Finally, dispersal in geological time is illustrated by the historical biogeography of the gymnosperm genus Agathis (Araucariaceae).