What is pollinating the critically threatened calcicolous plants in the Waitaki Valley?

Understanding the key pollinators of rare plants is important for a holistic assessment of ecosystem health, as the impact on a given species can travel through the network, affecting other species. Many specialist calcicolous (limestone-specific) plants are rare. Conservation management plans have been developed to assist in the survival of these rare plant species, but these rarely include information on pollinators. To increase our understanding of limestone ecosystem functioning, we investigated the pollinators of three critically threatened plant species, Lepidium sisymbrioides, Carmichaelia hollowayi, and Gentianella calcis subsp. calcis in two Otekaike limestone reserves, Wai O Toura Scenic Reserve and Waipata Scientific Reserve. We used community sampling and 10-minute observations to investigate which insect species are the most likely pollinators of these three plants species. Observed flower visitors were caught, identified, and swabbed for pollen. The ability to deposit conspecific pollen on stigmas was tested for selected insect species via single-pollinator visit assays to female L. sisymbrioides flowers. The community sampling experiments show that the most likely pollinators of L. sisymbrioides are the endemic bee, Lasioglossum sordidum, and Tachinid flies, including native Pales sp., and endemic Mallochomacquartia vexata. The most likely pollinator for G. calcis subsp. calcis is 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. The native bee Leioproctus pango is the most likely pollinator for C. hollowayi, as it was the most observed visitor and nearly all captured bees were carrying C. hollowayi pollen. This research contributes to the literature on New Zealand’s naturally uncommon ecosystems and provides an in-depth look into plant-pollinator interactions of these under-researched plant species.