Aspects of the ecology of Tupeia antarctica and its conservation management

Abstract

Mistletoes, a functional group of aerial stem hemiparasites, are considered to be keystone species in many ecosystems worldwide. Unfortunately, they have received little attention relative to their diversity, distribution and ecological importance. More specifically, one of New Zealand’s endemic Loranthaceae mistletoes, Tupeia antarctica, has not been the focus of a targeted research study in over 70 years despite being classified as ‘At Risk’ and ‘Declining’. More knowledge is required about this species given the sizeable time period that has passed, and the degree to which habitat modification and other threats are contributing to T. antarctica’s declining conservation status. T. antarctica, an endemic mistletoe species of New Zealand is under threat due to a variety of factors such as introduced mammalian herbivores, low seed establishment and habitat destruction. Like many parasitic plants, T. antarctica requires the involvement of two key mutualists, insect pollinators and avian frugivores, in order to successfully reproduce and establish. Pollen is most likely transferred by small Diptera (fly) species while avian frugivores disperse the seeds to suitable establishment sites on eligible host species. This thesis aimed to explore (1) the general ecology and distribution of Tupeia antarctica, focusing on the species’ current distribution in New Zealand generally and the Otago region specifically, (2) the structure and specificity of Otago populations, (3) morphological and sex-linked variation in leaf traits, (4) seed establishment processes, and (5) the effects of herbivory on gall like T. antarctica infections.

This study found that the current distribution of T. antarctica is significantly more restricted than historically recognised, despite the fact that species modelling suggests a wider distributional range throughout New Zealand and within Otago is achievable for the species. Only three viable T. antarctica populations were identified within the Otago region. Within these, T. antarctica tended to be aggregated on large, old host trees. Although T. antarctica is recognised as a generalist mistletoe (i.e. able to parasitise a wide range of host species), two key hosts were favoured within Otago; Carpodetus serratus and Plagianthus regius. Furthermore, different host preferences were recognised at both a regional and population level. Morphological features varied with latitudinal gradients across New Zealand, which is likely indicative of climate and ecotype variations at different locations. However, leaf features were not useful for distinguishing between male and female plants. Seed translocation trials failed to successfully establish any new T. antarctica individuals; presumably a larger sample size and host breath is needed to observe success. Lastly, introduced herbivorous mammals such as Trichosurus vulpecula (common brushtail possum) and Rattus species (rats) significantly impacted T. antarctica growth by grazing on plants at all study sites in Otago. The Dunedin Town Belt T. antarctica population was most greatly affected by these pests and it is likely minimal recruitment occurs in this population. In light of these findings, a management plan was produced which outlines all current threats and ways these factors can be mitigated for the ongoing survival and increased recruitment of the species.