Local geographic distributions of bumblebees, near Crested Butte, Colorado: competition and community structure.

Seven of 12 species of bumblebees accounted for 97% of all bumblebees observed. These 7 species form 4 groups in terms of both their proboscis lengths and the corolla lengths of the plants they preferentially visit. Long-, medium-, and short-tongued groups were most often observed foraging at flowers with long, medium, and short corollas, respectively. Proboscis lengths tended to be very similar within each group but quite dissimilar between groups. The 4th group consisted of a single short-tongued species which has well- developed mandibles which enable it to rob nectar from many plants with long corollas. It also feeds legitimately on short-corolla flowers. When the data on bumblebees and plant distributions are combined with data on flower preferences, a pattern consistent with a competition hypothesis emerges. Within each proboscis-length group, bumblebee species tend to replace one another altitudinally in a manner consistent with the hypothesis.-from Author