Department of Biology at the University of Rochester

Comparison of the number of species of oligolectic and polylectic bee species on
the same host plants. Data from (A) Mexico - Arizona border, Minckley and
Roulston (unpublished); (B) 451 plant species in southern Germany, Westrich
(1990); (C) Carlinville, Illinois, USA, Robertson (1928, plant families
Asteraceae, Malvaceae, Onagraceae, and Verbenaceae); and (D) subtropical Brazil,
Schlindwein (1998). (E) compares the number of polylectic bees hosted by plant
species that also host oligolectic bees (black) or do not also host oligolectic
bees (gray). Differences in total number of species between sites partially
reflect sampling intensity. From, Minckley, R.L., & T.H. Roulston. (2006)
Incidental mutualisms and pollen specialization among bees, pp. 69-98. In,
Plant-Pollinator Interactions: From Specialization to Generalization. Waser,
N.M. and J. Ollerton (eds.), Univ. of Chicago Press

Like most groups of insects, many bee species are specialists on one or several closely-related plant species. Yet unlike herbivores which have a negative impact on their host, bees transfer pollen among plants. Presumably, this pollinator function means bees have a positive impact on the relationship with their host and this has consequences to how plant-pollinator interactions evolve and are maintained.

We are finding that differences among plant-pollinator interactions and plant-herbivore interactions are less than might be expected. Patterns of floral host use by bees in the San Bernardino Valley (and elsewhere) are that plants which host specialist bees are often involved in very generalized interactions with the pollinator community. Plants that attract specialist and generalist bee species appear to be those that are unusually productive in terms of the resources they offer to the pollinator community and have flowers which are open and easy to forage from by most pollinators. Rather than being involved in tight, coevolved interactions with their floral host, specialist bees participate in generalized interactions that involve many other bee species in the community.