Patterns of Resource Utilization in Two Fennoscandian Bumblebee Communities

We studied seasonal changes in food niche relations among species in two Fennoscandian bumblebee communities. A community in southern Finland composed of 8 species utilized altogether 59 flower species during the whole summer. Corresponding figures for a community in northern Sweden were 9 bumblebee species and 50 flower species. Three bumblebee species were common to both communities. The flowering periods of the resource plants were longer in the southern community than in the northern one. In the southern community, but not in the northern one, the observed weekly niche overlaps were smaller than those to be expected assuming random foraging. During the whole season most species utilized more than 15-20 flower species in both areas, concentrating, however, most of their visits to a few of them. Niche overlaps (whole season combined) and differences between the frequency distributions of proboscis length and utilized corolla tube depths, respectively, were smaller in the southern community than in the northern one. These discrepancies may be due to a more stable resource production in the southern community contributing to a more intensive competition between species.