Habitat and Food Utilization in a Subarctic Bumblebee Community

We studied the seasonal dynamics of habitat and food utilization among bumblebee species in a community on the slope of a subarctic mountain (340-1050 m a.s.l.). During the summer all species at times utilized the whole altitudinal range. During spring all species foraged in the basal parts of the mountain, and during autumn in the intermediate zone. The altitudinal utilization of the mountain slope was the most diverse in the middle of the season. The observed weekly habitat niche and the food niche overlaps did not deviate from the overlaps calculated on the assumption of random habitat or food utilization, respectively. The segregation with respect to food was more complete than with respect to habitat. When the overlaps were calculated on the pooled, whole-season observations, a positive correlation was found between the pairwise habitat and food niche overlaps. The bumblebees separated into subalpine species (Bombus pratorum (L.), B. jonellus (K.), B. pascuorum Scop. and B. lucorum (L.)) and into alpine species (B. hyperboreus Schon., B. polaris Curt. and B. alpinus (L.)). The species, B. lapponicus (Fabr.) and B. balteatus Dahlb., utilized the whole altitudinal range. Probable factors affecting the altitudinal distribution patterns are discussed.