Abstract
The rapid decline of New Zealand’s rare habitats is a major threat to biodiversity and ecosystem services. Limestone is one such rare habitat, and the plants that reside only in limestone are threatened. Conservation management plans have been developed to assist in the survival of these species. Creating a conservation strategy for an endangered or threatened plant species should include discovering how a species reproduces. Many plants use cross-pollination as their method of sexually reproducing; yet, most management plans do not factor in pollination, and if they do, they do not identify the key pollinators. Understanding the key pollinators is important for the assessment of the ecosystem as a whole, as the impact on a given species can travel through the network, affecting other species. To genuinely conserve a plant, effective management should encompass all components of its ecosystem. Considering this and the already existing global pollinator crisis, I aim to demonstrate the importance of pollinators in conserving rare endangered limestone plant species, by investigating the pollinators of three critically threatened species, Lepidium sisymbrioides, Carmichaelia hollowayi, and Gentianella calcis subsp. calcis in North Otago Reserves, Wai O Toura Scenic Reserve and Waipata Scientific Reserve.
Chapter 1 is a literature review describing an uncommon ecosystem, limestone, and the focal plant species of this study. In Chapter 2, I investigate which species are the most likely pollinators of L. sisymbrioides, C. hollowayi, and G. calcis subsp. calcis, through community sampling and 10-minute visitor observations. I examine how several cofactors, such as weather conditions (e.g., temperature), affect insect visitation rates. I determine which species carry the pollen of the focal plant species, by referencing a pollen library that I developed for the two reserve sites (see Appendix). Furthermore, I use single-visit pollinator assays to determine whether conspecific pollen is being deposited onto female L. sisymbrioides plants. Observed insects were caught, frozen and identified to the lowest classification level possible. Insects were only considered to be effective pollinators if they carried pollen of the focal plant species. Single-visit pollinator experiment was done by bagging female L. sisymbrioides plants, then removing the bag and waiting for an insect to visit the unbagged flowers. Once visited, the flower head was removed and swabbed for L. sisymbrioides pollen.
The community sampling experiments show that many insect species visit L. sisymbrioides, but that the most effective pollinators are likely the endemic bee, Lasioglossum sordidum, and Tachinid flies, including native Pales sp., and endemic Mallochomacquartia vexata. It was confirmed that pollen is being deposited onto female L. sisymbrioides plants via insect pollinators, with Tachinid flies depositing the most pollen. Both plant size and temperature influence insect visitation to L. sisymbrioides, insects preferred to visit larger plants and had a preference towards warmer weather around 24oC. The most effective pollinator for G. calcis subsp. calcis is likely the endemic hover fly, Melanostoma fasciatum. This species was the most frequent visitor, with over half the hover flies captured carrying G. calcis subsp. calcis pollen. While location and temperature did not influence insect visitation, wind speed did. Insects visited more frequently when wind speeds were lower. Leioproctus pango is likely the most effective pollinator for C. hollowayi, with L. pango being the most observed visitor, and nearly all captured bees were carrying C. hollowayi pollen. The size of the C. hollowayi plants affects insect visitation with insects visiting larger plants more frequently, while temperature and wind do not appear to influence insect visitation.
The results of this study indicate that native and endemic insect pollinators are important in the reproductive system of Lepidium sisymbrioides, Carmichaelia hollowayi, and Gentianella calcis subsp. calcis. The research done in this thesis contributes to the literature on New Zealand’s naturally occurring uncommon ecosystems and provides an in-depth look into plant-pollinator interactions of these under- researched plant species. Further research should conduct a larger multiyear community sampling experiment as one season might not have been long enough to gather enough data. Further research should try a multiple-visit pollinator experiment to determine the seed set in the plants.