Sheep grazing influences the abundance, diversity, and community composition of wild bees and other insects in livestock pastures

Pollinators contribute to the establishment of perennial native forages, but little is known about the effect of grazing practices on pollinator abundance and diversity in livestock pasture ecosystems. Grazing reduces floral resources available to bees and other insects, and as a result, may influence their communities. The main objective of this study was to examine the impact of sheep grazing on bees and other non-bee insects in livestock pasture established with seed mixes of native forb/legume/grass and warm season grasses. Each pasture was divided into two halves (in a split-plot design) using an electric fence in which one plot was grazed and the other plot was non-grazed. Blue vane traps and a pair of yellow and blue pan traps were used for sampling bees and non-bee insects. A diverse array of bees (59 species) and non-bee insects (at least 93 species) were found in the livestock pastures. The abundance, diversity, and evenness of bee and non-bee communities were greater in nongrazed plots as compared to grazed plots. However, species richness, as measured by rates of species accumulation relative to sampling effort, was not different among treatments. Results show that a diverse community of bees and non-bee insects may be found in livestock pasture systems, but reduction in bee and non-bee insect diversity in grazed areas highlight the importance of strategic pasture management to support persistence of native forages and sufficient floral resources for pollinators at relevant scales.