Vagrant birds as a dispersal vector in transoceanic range expansion of vascular plants

Kalwij, Jesse M. University of Johannesburg. Department of Zoology. Centre for Ecological Genomics and Wildlife Conservation. South Africa.Medan, Diego. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Botánica General. Buenos Aires, Argentina.Kellermann, Jürgen. State Herbarium of South Australia. Department for Environment and Water. Adelaide, South Australia, Australia.Greve, Michelle. University of Pretoria. Department of Plant and Soil Sciences. South Africa.Chown, Steven L. Monash University. School of Biological Sciences. Victoria, Australia.4655, 19Birds are thought to be important vectors underlying the disjunct distribution patterns of some terrestrial biota. Here, we investigate the role of birds in the colonisation by Ochetophila trinervis (Rhamnaceae), a vascular plant from the southern Andes, of sub-Antarctic Marion Island. The location of O. trinervis on the island far from human activities, in combination with a reconstruction of island visitors’ travel history, precludes an anthropogenic introduction. Notably, three bird species occurring in the southern Andes inland have been observed as vagrants on Marion Island, with the barn swallow Hirundo rustica as the most common one. This vagrant displays long-distance migratory behaviour, eats seeds when insects are in short supply, and has started breeding in South America since the 1980s. Since naturalised O. trinervis has never been found outside the southern Andes and its diaspores are incapable of surviving in seawater or dispersing by wind, a natural avian dispersal event from the Andes to Marion Island, a distance of greater than 7500 km, remains the only probable explanation. Although one self-incompatible shrub seems doomed to remain solitary, its mere establishment on a Southern Ocean island demonstrates the potential of vagrancy as a driver of extreme long-distance dispersal of terrestrial biota