|Cane, James - Jim|
Submitted to: Ecological Applications
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/15/2005
Publication Date: 4/30/2006
Citation: Cane, J.H., Minckley, R., Kervin, L., Roulston, T., Williams, N.M. 2006. Complex responses within a desert bee guild (Hymenoptera: Apiformes) to urban habitat fragmentation. Ecological Applications. 16(2):632-644. Interpretive Summary: As natural habitats become isolated and fragmented, species composition and abundance on these "islands" change. We examine the consequences of half a century of urban habitat fragmentation on the native bee fauna associated with the dominant desert shrub, Larrea tridentata (creosote bush). We have systematically sampled bees at 59 fragments of known age, size and spatial isolation. Marked shifts in faunal composition have occurred as fragments have aged and shrunk in size. Cleptoparasitic species are largely absent. Habitat loss and disruption, and not fragmentation per se, accounts for the absence of a few specialist and generalist bee species from all fragments. The progressive loss of floral specialists among the ground nesting fauna is explicable by fragmentation and loss of suitable nesting sites rather than fragmentation of floral host populations. The sole cavity nester among Larrea specialists is proliferating in medium and small sized fragments, as are other native cavity nesting species in general. From the shrub's perspective, smaller, older, more isolated fragments are not suffering from diminished pollinator abundance. This unanticipated finding results from urban habitat alteration, being the increased availability of wooden nesting substrates provided in older residential neighborhoods relative to undeveloped desert scrub. Clearly, the effects of habitat fragmentation on native bee faunas must consider life history attributes other than mere floral association.
Technical Abstract: During the past 50+ years, urban habitat fragmentation has elicited contrasting responses from the guild of bees associated with Larrea tridentata (creosote bush), a flowering desert shrub that dominates the warm deserts of western North America and northern Mexico. Guild composition and native bee abundance at Larrea flowers in 59 sampled fragments shifted, sometimes dramatically, in response to fragment size and age. Only a few guild members were intolerant of urban fragmentation altogether. Unexpectedly greater densities of native bees were found visiting flowers of creosote bushes growing in the smaller fragments. A combination of two ecological attributes of bees - nesting substrate and taxonomic floral specialization - largely defined the 62 bee species' heterogeneous responses to fragmentation in this study. Ground-nesting (fossorial) Larrea specialists suffered most dramatically and consistently in incidence and abundance from urban fragmentation. Bees' responses to habitat fragmentation in this study were not predictable from habitat fragmentation studies dealing with mammals, birds or even other insects (beetles, butterflies), probably owing to bees' unique suite of biological attributes.