Abstract
Coevolution of efficient pollinators such as Bombus species (bumblebees) with the flowers they pollinate could make them spatially dependent on each other, thus affecting their distributions and abilities to colonize new areas. As Bombus species show a preference for blue-purple flowers, areas with a high diversity of tBombus species should correlate with a higher diversity of plants with blue-purple flowers. To investigate these relationships, we mapped flower colour distributions in the Arctic and tested for correlations with the richness of Bombus species and glaciation history. Regional occurrence and abundance of insect-pollinated species in the Arctic were obtained from the Panarctic Flora Checklist, and flower colour information for 526 species was retrieved from the literature, covering on average of 58% of each regional flora. The number of Bombus species within each floristic region was approximated from published distribution maps. Our results support the prediction that Bombus species have preference for blue-purple flower colour and that (re)colonization of species with blue-purple flowers in heavily glaciated areas is partly constrained by pollinator deficiency. Plant species with white flowers showed an opposite trend in distribution to species with blue-purple flowers. Less pollinator dependency due to alternative reproduction modes may explain the high abundance of white-coloured flowers in Arctic regions, as pigment production without the benefit of pollination to offset the energy cost may reduce fitness under marginal arctic conditions.