Impact of glacier retreat on biodiversity and plant-insect interaction dynamics

With the retreat and extinction of glaciers worldwide, new areas are exposed for colonization by diverse plants and associated insects. Yet, glacier retreat is also followed by the loss of plants and insects from local communities, causing changes in species diversity, species composition and plant-insect interactions. However, the impact of glacier retreat and extinction on pollination networks remains poorly understood. An integrative understanding of pollination network dynamics following glacier retreat is therefore of major importance to biodiversity maintenance and ecosystem functioning and services. Here, we addressed how glacier retreat affects directly and indirectly through biodiversity the frequency, complexity, and diversity of plant-insect interactions. After reconstructing the geochronology of glaciers (Mont Mine glacier, Swiss Alps), we surveyed plant-insect interactions and analyzed network dynamics. We observed sharp changes in the diversity of both plant and insect communities. We found an increase in the frequency of their interactions following glacier retreat, but an ultimate decrease with glacier extinction. Yet, after controlling for the effects of flower diversity, interaction frequency showed a regular, universal pattern. Accordingly, the complexity of pollination networks and interaction diversity tended to change at constant rates with glacier retreat. Our results indicate that, in the long-term, glacier retreat decreases biodiversity and influence the stability of ecological networks. The good news is that increasing flower diversity would counteract these impacts by increasing interaction diversity and complexity. Supporting plant and flower diversity may therefore be a key strategy for halting the erosion of ecological networks while increasing ecosystem functioning.