Decadal trends in arctic bumblebee floral preferences

Sammanfattning

Arctic warming is occurring at a rate two to three times faster than the global average, causing potential ecological consequences such as changes in community composition and shift in plant phenology. Both plants and pollinators are affected by phenological changes which may create a phenological mismatch between the pollinators and the plants they visit. However, it is unclear how bumblebees, being key pollinators of most Arctic plant species, are responding to these changes. To evaluate shifts in floral preferences over the three decades, a comparative study design which included field observation and microscopy analysis of samples collected in the field was used. Data on bumblebee foraging collected from Latnjajaure in the 1990s was compared with data collected during summer 2025. Pollen was collected from 65 queen bumblebees of six different species across the entire Latnjajaure valley. The phenology and abundance of the flowering species were estimated in three plots overlapping the area in which the historical floral data was recorded. The results show a change in the bumblebee foraging niche as Saxifraga oppositifolia a dominant early-season resource in the 1990s was absent from 2025 pollen loads. In contrast, Salix, a deciduous shrub emerged the early-season resource in 2025. This transition was accompanied by a significant contraction of the foraging niche as the median Shannon diversity Index (H′) dropped from 0.596 to 0.068. This narrowing shows high foraging constancy towards high-rewarding species such as Astragalus alpinus. While early flowering may affect the reproductive success of forbs like Saxifraga opp., the increase of shrubs such as Salix may provide the structural resilience necessary to maintain the plant pollinator network in the Arctic.