Dispersal of banana passionfruit (Passiflora tripartita var. mollissima) by exotic mammals in New Zealand facilitates plant invasiveness

Banana passionfruit (Passiflora tripartita var. mollissima) is a noxious vine that is invasive in forest patches in coastal regions throughout New Zealand. We investigated the dispersal mechanisms that facilitate its spread in the Marlborough Sounds. To find out which animals act as dispersers, we monitored tagged fruits in the field. Fruits were removed quickly after ripening. Significantly fewer fruits were wholly removed from off-road locations than locations on road edges, but removal was high in both cases (70% and 93% respectively) indicating likely dispersal by both humans and wild animals. We found no evidence of dispersal by birds, but infrared cameras documented possums and rats consuming fruits in the field. To investigate the effect of fruit handling on germination, we compared germination success between hand-cleaned seeds, fleshy seeds and intact fruits in the field and glasshouse. Seeds germinated readily in all treatments, with no significant difference between treatments, so seeds do not require frugivore handling to germinate. In addition, we measured the germination of seeds extracted from 1.5 kg of feral pig faeces collected from Sus scrofa at Te Weuweu Bay and from faeces from captive possums (Trichosurus vulpecula) and Norway rats (Rattus norvegicus). Seeds extracted from pig and possum droppings readily germinated, with final germination success not significantly different from hand-cleaned or in-flesh seeds. None of the few intact seeds excreted by Norway rats germinated. Banana passionfruit has formed invasive mutualisms for both pollination (with introduced bees) and dispersal (with introduced mammals), exacerbating its spread. Weed management should combine direct weed control with limiting the spread of banana passionfruit, by managing feral pigs and possums.