Pseudopanax arboreus: an Investigation of its Native Pollination System

Abstract

Pseudopanax arboreus is a winter-flowering, dioecious tree that is native to NewZealand. Despite its common presence in native forests, there is relatively little literaturepublished on it or its pollination system. Using only a pollination syndrome-based examinationof its inflorescences, P. arboreus appears to fit the generalized, insect pollination system thatwas initially and indiscriminately proposed for most New Zealand flora. However more recentstudies have recognized the wider reach of pollination systems in New Zealand, including someobservations of native bird visitors to P. arboreus in areas of the country.Our study investigated the pollination system of P. arboreus in Pureora Forest Park, ahighly protected area of native New Zealand forest, in an attempt to catalogue its interactionswith its evolved pollinators. Here we used both video recording and pollinator-exclusiontreatments to quantify the role of vertebrate and invertebrate visitors. Results of the pollinatorexclusion treatments indicated significant contribution to P. arboreus’s pollination by both insectand vertebrate visitors. Video recordings confirmed the role of insects as pollinators to P.arboreus, however no vertebrate visitors were observed in the recordings. Within the videofootage, there were significant differences in the duration of insect visitation from different sizeclasses of insect. We found that larger insects spent significantly more time on theinflorescences per visit when compared to medium or small insects. Similarly, the mediuminsect group spent significantly more time on the inflorescences per visit when compared to thesmaller insects. These results highlight the generalized and indiscriminate nature of this plant’spollination system—where a wide variety of insect visitors within each size class were directlyobserved and the role of larger vertebrate visitors was indirectly confirmed. These finds haveimplications beyond the pollination system of the tree itself, suggesting that in the context ofNew Zealand’s native ecosystem, P. arboreus may be a crucial winter resource to many endemicspecies.