Rare plant’s need for native pollinators threatened by invasive plant-pollinator relationship

Many flowering plants rely on pollination for their reproductive success, but the introduction of non-native plants can impact these essential plant-pollinator relationships. Chloropyron maritimum ssp. maritimum is a rare salt marsh plant that has been known to benefit from insect pollination, and its habitat is being encroached on by the non-native Limonium duriusculum. We use plant-pollinator observation, network analysis, and small-scale experimental removal of L. duriusculum to understand which insects are visiting C. maritimum maritimum, and the impact, if any, of L. durisiculum on C. maritimum maritimum pollination and the plant-pollinator network. We documented infrequent visitation to C. maritimum maritimum at the Carpinteria Salt Marsh, California, USA, with native bees being the only observed C. maritimum maritimum visitors. We found that the pollinator composition of C. maritimum maritimum and L. duriusculum were significantly different. The vast majority (96%) of L. duriusculum visitors were two non-native insect species (Hymenoptera: Apis mellifera and Diptera: Eristalinus aeneus), neither of which entered C. maritimum maritimum flowers. The experimental removal of L. duriusculum had no effect on C. maritimum maritimum visitation. However, the plant-pollinator network was more nested, more connected and had higher specialization when L. duriusculum was removed. Future studies should implement larger-scale removal to further investigate these findings. Additionally, subsequent work should investigate if there is adequate nesting habitat for C. maritimum maritimum pollinators in surrounding areas, to ensure the survival of the few plant-pollinator interactions this rare plant currently maintains.