Comparing Foraging Niches Of Newly Sympatric Bumble Bees In Alpine Habitats Of Colorado

Global climate change has facilitated upward range shifts of bumble bees in mountainous habitats worldwide, increasing species richness and competition for floral resources. Competition for flowers is predicted to occur between bees with similar traits relevant to foraging, especially tongue length. I assessed competition between two newly sympatric short-tongued bees: Bombus sylvicola, a native alpine bee, and B. bifarius, a subalpine species that has become prevalent above treeline. I allowed individuals to forage on inflorescence arrays comprised of seven species of bee-pollinated alpine plants. All measures of preference reflected overlapping diet niches for B. sylvicola and B. bifarius. Mean visitation frequencies to the seven plant species were nearly identical for both bumble bees, as were inflorescence foraging times and floral species fidelity during transitions. Results suggest that the arrival of B. bifarius above treeline has resulted in competition between the morphologically similar bees for available floral resources.