Short-term responses of native bees to livestock and implications for managing ecosystem services in grasslands

Rangelands are significant providers of ecosystem services in agroecosystems world‐wide. Yet few studies have investigated how different intensities of livestock grazing impact one important provider of these ecosystem services—native bees. We conducted the first large‐scale manipulative study on the effect of a gradient of livestock grazing intensities on native bees in 16 40‐ha pastures in the Pacific Northwest Bunchgrass Prairie. Each pasture was exposed to one of four cattle stocking rates for two years and grazing intensity was quantified by measuring utilization. We measured soil and vegetation characteristics related to floral and nesting resources as well as several metrics of the bee community. Increased grazing intensity significantly reduced vegetation structure, soil stability, and herbaceous litter and significantly increased soil compaction and bare ground. Native bees responded with changes in abundance, richness, diversity, and community composition. Responses varied with taxa and time of season. Bumble bees were sensitive to grazing intensity early in the season, showing reduced abundance, diversity, and/or richness with increased intensity, potentially because of altered foraging behavior. In contrast, sweat bees appeared unaffected by grazing. These results show that native bee taxa vary in their sensitivity to livestock grazing practices and suggest that grazing may potentially be a useful tool for managing pollination services in mosaic agroecosystems that include rangelands

Delivery of crop pollination services is an insufficient argument for wild pollinator conservation

There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments

A revision of the bees of the genus Andrena of the Western Hemisphere. Part XV???Subgenus Hesperandrena.

This work reports on a study of 1,200 specimens segregated into 9 species, 4 of which are new to science. One name is relegated to synonymy. The relationships within the subgenus and with other subgenera of Andrena are briefly discussed. The subgenus Hesperandrena was recognized and described by Timberlake in Lanham 1949 (p. 208) to include two previously described species, Andrena escondida Cockerell and Andrena baeriae Timberlake. These two species have in common a propodeum which, Timberlake described as having the dorsal surface, ???... broad, gently curved and inclined from base to apex, without definite truncation, the lateral margins distinctly carinate and convexly arcuate.??? This is the main character separating this subgenus (Fig. 4) from other subgenera of Andrena except that in the males of Hesperandrena the lateral margins of the propodeum are not carinate. Other characters are given in the description of the subgenus below. The species of this subgenus are very similar to one another and difficult to tell apart. The species are known only from California and Baja California. The reader is referred to earlier sections of this revision (LaBerge 1967, 1969, 1971, 1973, 1977, 1980, 1986, 1987, 1989; LaBerge and Bouseman 1970, 1987; LaBerge and Ribble 1972, 1975; Bouseman and LaBerge 1979; Thorp 1969; Donovan 1977) for details of morphology and a more complete bibliography on the genus Andrena. No new terms have been introduced and the bibliography presented here includes only references cited. Published locality and floral records are included in the sections at the end of each species account.published or submitted for publicationis peer reviewe

A List of Bees of Santa Cruz Island, CA

An unpublished checklist of bees created by Dr. Robbin Thorp of Santa Cruz island in 2007.&nbsp