High mountain plant-pollinator interactions: the case study of the narrow endemic alpine plant Androsace brevis (Hegetschw.) Ces. (Primulaceae)

Background and Aims – Global warming may threaten mountain ecosystems by altering plant-arthropod interactions, for instance by causing phenological mismatches between flowering time and pollinator activity. Especially plants having an early and short flowering period may be at risk, since an earlier snowmelt can lead to a greater anticipation of flowering than pollinators emergence. Here we study the structure of a high mountain plant-pollinator network by taking the narrow endemic Androsace brevis (Hegetschw.) Ces. as an example of an early flowering plant species. Methods – Fieldwork was conducted in the Orobian Alps (Bergamo, Italy) for three years and in the Lepontine Alps (Como, Italy) for two years. Androsace brevis flower-visiting arthropods were sampled with the timed observation method. In addition, we sampled pollen of each blooming plant species within a radius of 500 meters around the focal plant to create a pollen library. Arthropods were identified to the lowest possible taxonomic level and quali-quantitative pollen analyses were performed to identify actual pollinators. To achieve this, pollen grains carried by arthropods were isolated, acetolysed, prepared for light microscopy observation and identified with the help of the pollen library and pollen identification keys. After creating a plant-pollinator matrix, we obtained quantitative plant-pollinator networks by bipartite analysis with RStudio Software. Results – We identified 50 arthropod families, and could attribute the pollen samples to 25 plants species. We identified Diptera (Anthomyiidae) and Hymenoptera (Apoidea) as main pollinators of A. brevis. Moreover, we observed well-structured plant-pollinator networks, with many links between plants and arthropods, despite the early flowering period of A. brevis. Conclusions – Our results contribute to a better understanding of the pollination biology of A. brevis. More generally, our results give insight into high mountain early-season plant-pollinator networks, which are important but little-known and potentially vulnerable components of high-mountain ecosystems.