The interactive impacts of early snowmelt and topography on plant-pollinator interactions in an alpine ecosystem

Background/Question/Methods

Anthropogenic climate change is altering interactions among species, including plants and pollinators. Plant-pollinator interactions, crucial for the persistence of most plant and many insect species, are threatened by climate change-driven phenological shifts. Phenological mismatches between plants and their pollinators, which may be impacted by landscape topography, can affect pollination services. Simulations indicated that these mismatches may reduce floral resources available to up to 50% of insect pollinator species. Although alpine plants rely heavily on vegetative reproduction, seedling recruitment and seed dispersal are likely to be important drivers of alpine community structure. Some species of alpine plants at the Niwot Ridge Long Term Ecological Research site have displayed advanced phenology under treatments of advanced snowmelt (Forrester, unpublished data). Here we ask how experimentally induced changes in snowmelt timing interact with topography to impact the timing of flowering and plant-pollinator interactions. Additionally, we ask how advanced snowmelt timing impacts plant-pollinator phenological overlap. To determine if pollinator visitation rate and species richness differ between early snowmelt and control plants, we performed pollinator observations on all flowering plants in plots where snowmelt timing was experimentally advanced using inert black sand and in plots with unmanipulated snowmelt timing.

Results/Conclusions

We found that plots with experimentally advanced snowmelt timing experienced peaks in insect pollinator visitation rates and diversity earlier than plots with unmanipulated snowmelt. This is likely due to the advanced floral phenology of certain key species in these plots. We then used structural equation models to describe the interactive effect of topography and black sand treatment on snowmelt timing, floral phenology, and insect visitation to flowers; these models show that both snowmelt timing and topography interact to predict the timing of floral abundance, which impacts pollinator visitation rate. Finally, we calculated the overlap between plants and their known pollinators, then used a series of structural equation models to compare this overlap in plots with experimentally advanced and control snowmelt. This final component demonstrates the impacts of early snowmelt on phenological overlap of plants and their insect pollinators. Our findings elucidate the effects of early snowmelt on the plant and insect mutualists, as well as their interactions, of this alpine tundra ecosystem. Additionally, this study highlights the importance of taking landscape topography into consideration when predicting the impacts of climate change on plant-pollinator interactions.