Asynchronous range shifts drive alpine plant–pollinator interactions and reduce plant fitness

• Published in: Global change biology 2020-05, Vol.26 (5), p.3052-3064
• Main Authors: Richman, Sarah K., Levine, Jonathan M., Stefan, Laura, Johnson, Christopher A.
• Format: Article
• Language: English
• Subjects: alpine ecosystems; Bees; Climate; Climate change; community ecology; Global warming; Herbivores; migration; mutualism; Plant communities; Plant populations; Plant reproduction; pollination; Pollinators; range shifts; Reproduction; Reproduction (biology); Species; Temperature gradients; Transplantation
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15041

Climate change is driving species' range shifts, which are in turn disrupting species interactions due to species‐specific differences in their abilities to migrate in response to climate. We evaluated the consequences of asynchronous range shifts in an alpine plant–pollinator community by transplanting replicated alpine meadow turfs downslope along an elevational gradient thereby introducing them to warmer climates and novel plant and pollinator communities. We asked how these novel plant–pollinator interactions affect plant reproduction. We found that pollinator communities differed substantially across the elevation/temperature gradient, suggesting that these plants will likely interact with different pollinator communities with warming climate. Contrary to the expectation that floral visitation would increase monotonically with warmer temperatures at lower elevations, visitation rate to the transplanted communities peaked under intermediate warming at midelevation sites. In contrast, visitation rate generally increased with temperature for the local, lower elevation plant communities surrounding the experimental alpine turfs. For two of three focal plant species in the transplanted high‐elevation community, reproduction declined at warmer sites. For these species, reproduction appears to be dependent on pollinator identity such that reduced reproduction may be attributable to decreased visitation from key pollinator species, such as bumble bees, at warmer sites. Reproduction in the third focal species appears to be primarily driven by overall pollinator visitation rate, regardless of pollinator identity. Taken together, the results suggest climate warming can indirectly affect plant reproduction via changes in plant–pollinator interactions. More broadly, the experiment provides a case study for predicting the outcome of novel species interactions formed under changing climates. Differences in species' responses to climate change are driving climate‐induced disruption of species interactions. We experimentally disrupt plant–pollinator interactions in the Swiss Alps by transplanting high‐elevation plant communities to lower elevations, and test for differences in floral visitor community composition, floral visitation rate, and seed production in three high‐elevation plant species. We find species‐specific reduction in seed production at low elevations accompanied by floral visitor community turnover across the elevation gradient, indicating the potentia