Biological impediments to measures of competition among introduced honey bees and desert bees (Hymenoptera: Apiformes)

Foraging behaviors, host plant breadth, and agilities of social and solitary bee species differ dramatically. We illustrate how these phenomena can obscure the effects of floral resource competition from our studies on a species-rich, native bee fauna that visit the flowers of creosote bush [Larrea tridentata Coville (Zygophyllaceae)], a widespread dominant perennial plant species in the warm deserts of North America. The potential for competition among the solitary bees that visit creosote bush and honey bees was investigated by two methods: one that is widely used asks if solitary bee abundance and species diversity is less at sites with greater honey bee abundance; and a second. more novel approach that asks if pollen availability is limiting at sites with high bee biomass. We found no relationship among number of honey bees at sited and species richness and abundance of all native bees combined or of Pollen specialist species considered alone. Protein represented in the pollen of the primary host plant greatly exceeded the biomass of bees present at a site. We suggest bee populations are rarely pollen limited in this system or that competition, when it occurs, is highly episodic. Future studies of bee competition will need to assess long-term Population variation among solitary and introduced bees in habitats where floral resources can be measured for multiple flowering plant species, and where bee colony/nest dynamics can be documented, Studies of bee faunas in temperate areas are needed. This paper demonstrates some of the possible pitfalls for studies of competition among highly eusocial and solitary bees, We conclude that basic data (in bee biology and population dynamics are needed before these questions can be satisfactorily answered and, at present, little hard data are available to evaluate the competing hypotheses