Document: JAM-3-82-40

Pollinator guild composition shifts with 70 years of habitat fragmentation: The bees of Larrea.

CANE, J.H.* ¹, R.MINCKLEY ², L.KERVIN ¹ and T'AIROULSTON ³

Utah State University, Logan, UT 84322-5310 USA ¹
University of Utah, Salt Lake City, UT 84112 USA ²
North Carolina State University, Raleigh, NC 27695-7613 USA ³

Abstract:
As natural habitats become isolated and fragmented, species composition and abundance on the remnant "islands" change. We examine the consequences of half a century of urban habitat fragmentation on the native bee fauna (61 spp) associated with the dominant desert shrub, Larrea tridentata (creosote bush). We have systematically sampled 2512 native bees at 59 habitat fragments of known age, size and spatial isolation. Marked shifts in faunal composition occurred as fragments aged and shrunk in size. Cleptoparasitic species became less frequent. Habitat loss and disruption, and not fragmentation per se, accounted for the absence of a few specialist and generalist bee species from all fragments. The progressive loss of 5 floral specialists among the ground-nesting fauna was explicable by fragmentation and loss of suitable nesting sites rather than fragmentation of floral host populations. The sole cavity-nester among Larrea specialists, Hoplitis biscutellae, proliferated in smaller fragments, similar to most other native cavity-nesting species. This unanticipated finding results from urban habitat alteration, which increased the availability of wooden nesting substrates provided in older residential neighborhoods relative to undeveloped desert scrub. Bees are well-adapted for life in patchy environments. The distribution and density of altered nesting substrates profoundly influences bee species' responses to fragmentation of floral host populations. Creosote bushes growing in smaller, older, more isolated neighborhood fragments are more intensely visited by native desert bees than are bushes found in larger and younger fragments. The prolonged persistence of much of this diverse native bee guild in fragments of modest size offers hope for native pollinator conservation.

Keywords: bees, Apoidea, habitat fragmentation, pollinator, guild, conservation

This abstract is being presented at: 3:30 PM in session:
CONSERVATION ECOLOGY