Dispersal, Germination and Survival of New Zealand Mistletoes (loranthaceae): Dependence on Birds

Mistletoes are stem hemiparasites, which grow on the branches of a host tree or shrub and take water, water-conducted nutrients and organic solutes from the host’s xylem. There are two major mistletoe families, Loranthaceae and Viscaceae. The Loranthaceae are principally Southern Hemisphere in distribution, with between 50 and 80 genera (Barlow, 1983). New Zealand has six native species in the Loranthaceae. All have declined in abundance since European settlement. The decreases are attributed to habitat loss and introduced herbivores, especially the Australian brushtail possum (Trichosurus vulpecula Kerr) (Ogle and Wilson, 1985; Norton, 1991). In this paper we present evidence of the dispersal, germination and establishment of the New Zealand Loranthaceae, and evaluate to what extent their decline may be a secondary effect of reductions in numbers of their principal bird disperser species. In terms of Caughley (1994), we present data on the natural history of the species to determine which agents of decline may be most important. Almost all Loranthaceae species have fleshy animal-dispersed single-seeded fruits (morphologically pseudocarps). Mistletoes worldwide are well known for their close relationships with birds, both for pollination and for dispersal (e.g., Kuijt, 1969; Barlow, 1983; Ladley and Kelly, 1995a). Dispersal is particularly important (and difficult) for mistletoes because the safe site for a ripe seed is the branch of another suitable host tree. As a result, many mistletoes have close relationships with their avian dispersers (e.g., McKey, 1975). Despite the high specificity of some mistletoe dispersal systems, there are no recorded examples of obligate interdependence between a mistletoe species and a bird species throughout the geographical ranges of both mutualists (Reid, 1987a, 1991; Wheelwright 1988). JENNY J. LADLEY and DAVE KELLY