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United States Department of Agriculture

Agricultural Research Service

Title: Spatial Predictability and Resource Specialization of Bees (Hymenoptera: Apoidea) at a Superabudant, Widespread Resource

Authors
item Minckley, R - AUBURN UNIVERSITY
item Cane, James
item Kervin, Linda - UTAH STATE UNIVERSITY
item Roulston, T'ai - AUBURN UNIVERSITY

Submitted to: Biological Journal of the Linnean Society, London
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 9, 1998
Publication Date: N/A

Interpretive Summary: INTERPRETIVE SUMMARY Creosote bush, a shrub that dominates and defines the three great dese of western North America, hosts over 100 species of native bees, nearly 1/4 which are restricted to this shrub for all of their pollen needs. We have sampled bees visiting flowering creosote bush at forty-three 1-ha sites on public lands during spring bloom. We found that some bee species of both pollen specialists as well as generalists are abundant and ubiquitous at this shrub, but most species are highly variable in their abundance and their presence from site to site. S within 250 km of each other are more likely than not to share similar fauna bees, but beyond that distance, one cannot predict which elements of the li possible species will compose the local fauna of bees at creosote bush. We conclude that multiple populations of a flowering plant species mu sampled throughout the plant's geographic range in order to characterize it pollinator fauna. Furthermore, it appears that no one pollinator species i consistently and reliably abundant enough to provide pollination service throughout a plant's geographic range. Protecting a plant's pollinator fau will require conserving multiple populations and their attendant pollinator faunas.

Technical Abstract: ABSTRACT For reciprocal specialization (coevolution) to occur among floral visi and their host plants the interactions must be temporally and spatially per nt. However, studies repeatedly have shown that species composition and rel l abundance of floral visitors vary dramatically at all spatial and tempora es. We test the hypothesis that, on average, pollen specialist bee species more predictably at their floral hosts than pollen generalist bee species. nomic floral specialization reaches its extreme among species of solitary, n-collecting bees, yet few studies have considered how pollen specializatio floral visitors influences their spatial constancy. We test this hypothesis g an unusually diverse bee guild that visits creosote bush (Larrea tridenta the most widespread, dominant plant of the warm deserts of North America. T T-two strict pollen specialist and 80+ generalist bee species visit Larrea s floral resources. The sites we sampled were separated by 0.5 to >1450 km, spanned three distinct deserts and four vegetation zones. We found that species of Larrea pollen specialist bees occurred at mor es and tended to be more abundant than generalists. Surprisingly, spatial t er was high for both pollen specialist and generalist bee species at all di es, and species composition of samples from sites 1-5 km apart varied as mu repeat samples made at single sites. Nevertheless, the pattern of bee spec urnover was not haphazard. As distance among sites increased faunal similar f sites decreased. Faunal similarities among sites within 250 km of each ot ere generally greater than if randomly distributed over all sites (the null l). No single ecological category of species (widespread, localized, Larrea

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