Bird dispersal of loranthaceous mistletoes to remote Pacific islands: symbiosis in default

Mistletoes of the family Loranthaceae have characteristically low dispersibility. Whereas the family is represented by c. 400 species on the continental masses and intervening archipelagos on the western Pacific rim, and by a similar number in South America, only a few species have reached remote South Pacific islands. Recent bird dispersal of Ileostylus micranthus from New Zealand to Norfolk I (c. 700 km) is comparable in distance with island-to-island bird dispersal in the most widespread species, Decaisnina forsteriana, from New Guinea to the Marquesas in Quaternary time. Once established in island communities, even species of generally low dispersibility may have an increased probability of further waif dispersal. For mistletoes a shift in avian vectors is the likely cause, from berrypeckers (Dicaeidae) in Malesia-Australia to probably campephagids (Campephagidae), glossy starlings (Sturnidae) and fruit doves and imperial pigeons (Columbidae) in the Pacific islands. This shift has disrupted the association which exists between mistletoes and their specialized co-adapted bird dispersal agents in their continental source area on the western Pacific rim. When the mistletoe fruits become exclusively available to more generalist feeders, dispersal may be less efficient but extend over longer distances.