Effects of pollinator loss on endemic New Zealand mistletoes (Loranthaceae)

The endemic mistletoes Peraxilla colensoi and P. tetrapetala (Loranthacene) have declined considerably in New Zealand since 1840, reputedly because of introduced herbivores but coincident with a major decline in natize bird d ensities. We show that at two South Island sites (Craigieburn and Ohau) the re are too fete bird pollinators visiting the flowers to allow full fruit s et. We studied pollination rates in P. colensoi at Wakefield and P. tetrape tala at Craigieburn over four flowering seasons and P. tetrapetala in one s eason at Ohau. Supplemental hand pollination increased fruit production 1.2 5-5.3 times at Craigieburn and Ohau but not nt Wakefield. Excluding birds b y covering mistletoes with mesh bags decreased fruit set significantly nt W akefield but had little effect at Craigieburn and Ohau. Bellbirds (Anthorni s melanura) and Tuis (Prosthemadera novaeseelandiae) visited flowers signif icantly mole often at Wakefield than at Craigieburn. A lack of pollen tribe s in the style, not self-incompatibility or resource shortage caused the lo w fruit production in unmanipulated flowers at Craigieburn. Thus, at the tw o P. tetrapetala sites (Craigieburn and Ohau) fruit set tons chronically po llen limited whereas P. colensoi at Wakefield was not pollen-limited. Data from other Peraxilla sites also suggest pollination failure. Our study sugg ests that the conservation of Peraxilla species will require maintenance of native bird populations This and Bellbirds are important pollinators and d ispersers of nanny other New Zealand plants, and the breakdown of such mutu alistic relationships may have widespread consequences.