Resource utilization by bumblebee queens, workers and males in a subarctic area

Abstract

We studied the seasonal dynamics of food niche width and annual niche relations of queens, workers and males of six abundant bumblebee species living on a slope of a subarctic hill in North Sweden. The basic data consist of analyses of pollen contents in nectar loads of individual foragers. At any given time of the season individual foragers utilized frequently more than one flower species during each trip, concentrating, however, most of their efforts on one species only. These “major” species varied between individuals thus widening the foraging niche of the species. No obvious differences were observed in niche widths of the sexes and castes of the species (neither day‐to‐day nor annual observations). Queens had highest niche overlaps and males the lowest ones. Sexes and castes were separated into groups by their foraging patterns. Differences in proboscis lengths are not obvious niche separating factors at the study area. The environmental uncertainty (in time and space) may occasionally lead to excess of resources, which, in turn, may open possibilities of wide utilization of available flower species, thus rendering close fit between proboscis length and corolla tube depths of the foraged flowers unnecessary.