Convergent morphology and divergent phenology: Competition avoidance in two long-tongued bumble bee species (Hymenoptera: Apidae: Bombus)

Exploitative competition for floral resources is well documented in bumble bees and is thought to have shaped the difference in glossa lengths observed among species. Nectar-foraging efficiency increases if corolla length and glossa length are well matched, and species often exhibit preferences for flowers with corollae that match the lengths of their glossae. This foraging efficiency can influence the outcome of interspecies competition, and it has been hypothesized that a resource-limited bumble bee community can only consist of species with non-overlapping glossa lengths. However, phenological separation is another, overlooked mechanism for competition avoidance that can shape bumble bee communities and lessen the negative impact of resource sharing. Here we show that two species, Bombus auricomus (Robertson) and B. pensylvanicus (DeGeer) with similar glossa lengths overlap in their plant preferences, yet their temporal separation frees them from direct competition with one another. This suggests a novel pathway to explain why some bumble bee communities are more speciose than present competition-based theories allow.