Plant-pollinator interactions in the alpine: Landscape heterogeneity acts as a potential buffer against climate-change induced mismatch in the pollinator-generalist Ranunculus acris

Abstract

Phenology changes are a common response to global warming and the timing of phenological events is important for symbiotic interactions, such as pollination. If symbiotic species respond differently to global warming, this could lead to loss of facilitative interactions due to phenological mismatches between species. Global warming is faster and stronger in alpine regions, which could induce stronger asynchrony in plant-pollinator interactions in alpine habitats. However, most alpine plant species are pollinator-generalists and thus are expected to be less vulnerable to plant-pollinator mismatches. This study investigates plant-pollinator interactions in the pollinator-generalist plant species Ranunculus acris L. along a snowmelt gradient in the alpine area of Finse in western Norway over two growing seasons (2016 and 2017). The snowmelt gradient creates patches with different times of snowmelt, and thus onset of flowering. I use the spatial distribution of flowering and pollinator activity to investigate whether sub-populations with different times of flowering experience different synchrony with their pollinators, assessing the potential for temporal plant-pollinator mismatches. In addition, I conduct a hand-pollination experiment to investigate whether a sub-population’s synchrony with its pollinators affects plant reproductive ability. Plant-pollinator mismatch was not detected between R. acris and its pollinators in any of the snowmelt stages or years. Pollinator visitation rate was constant throughout the seasons of both years, but pollinator activity was lower for individuals flowering later in the season in 2017. Reproductive output was not found to be pollen limited, although lower achene mass correlates with lower pollinator visitation rates in late-flowering individuals in 2017. I conclude that this pollinator-generalist is well synchronised with its pollinators, and that early flowering might be related to higher reproductive success, meaning that earlier snowmelt and flowering should not be problematic for this species, but later snowmelt and flowering might. In addition, I suggest that the patchiness of this kind of heterogeneous alpine landscape contributes to flowers always being available to insects, and for pollinators to move between the patches of highest flower abundance, which lowers the risk of temporal plant-pollinator mismatch.