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Cane, J. H., R. L. Minckley, L. J. Kervin, T. H. Roulston, and N. M.
Williams. 2006. Complex responses within a desert bee guild (Hymenoptera:
Apiformes) to urban habitat fragmentation. Ecological Applications
<b>16</b>:632-644.<br><br>
Urbanization within the Tucson Basin of Arizona during the past 50+ years
has fragmented the original desert scrub into patches of different sizes
and ages. These remnant patches and the surrounding desert are dominated
by
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<i>Larrea tridentata</a></i> (creosote bush), a long-lived shrub whose
flowers are visited by >120 native bee species across its range.
Twenty-one of these bee species restrict their pollen foraging to
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<i>L. tridentata</a></i>. To evaluate the response of this bee fauna to
fragmentation, we compared species incidence and abundance patterns for
the bee guild visiting
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<i>L. tridentata</a></i> at 59 habitat fragments of known size (0.002–5
ha) and age (up to 70 years), and in adjacent desert.<br><br>
The 62 bee species caught during this study responded to fragmentation
heterogeneously and not in direct relation to their abundance or
incidence in undisturbed desert. Few species found outside the city were
entirely absent from urban fragments. Species of ground-nesting
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<i>L. tridentata</a></i> specialists were underrepresented in smaller
fragments and less abundant in the smaller and older fragments. In
contrast, cavity-nesting bees (including one
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<i>L. tridentata</a></i> specialist) were overrepresented in the habitat
fragments, probably due to enhanced nesting opportunities available in
the urban matrix. Small-bodied bee species were no more likely than
larger bodied species to be absent from the smaller fragments. The
introduced European honey bee,
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<i>Apis mellifera</a></i>, was a minor faunal element at >90% of the
fragments and exerted little if any influence on the response of native
bee species to fragmentation. Overall, bee response to urban habitat
fragmentation was best predicted by ecological traits associated with
nesting and dietary breadth. Had species been treated as individual units
in the analyses, or pooled together into one analysis, these response
patterns may not have been apparent. Pollination interactions with this
floral host are probably not adversely affected in this system because of
its longevity and ability to attract diverse pollinators but will demand
careful further study to understand.<br>
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