A meta-analysis of the effects of habitat aridity, evolutionary history of grazing and grazing intensity on bee and butterfly communities worldwide.
A variety of habitat-associated factors moderate effects of grazing on insect biodiversity. Here, we examine how aridity, evolutionary history of grazing and grazing intensity individually and interactively mediate the effect of livestock grazing on pollinator biodiversity (native bees and butterflies). Using a meta-analysis of 59 studies published in the primary literature, we characterized the response of pollinator communities to grazing across several continents. In very humid habitats, high grazing intensities generally had negative impacts on pollinator abundance and richness, but these effects were not found in semi-arid habitats, where livestock grazing intensity did not interact with aridity to impact pollinator abundance or richness. However, within semi-arid habitats livestock grazing was associated with reduced pollinator richness in areas with short evolutionary histories grazing. Pollinator life history mediated effects of livestock grazing on pollinator communities: livestock grazing had negative impacts on richness of social bees and butterflies but not solitary bees, though abundances of all three pollinator categories were consistently reduced under livestock grazing. Our synthesis suggests that effects of cattle on pollinatorsmay be driven by impacts on nesting habitats (e.g. soil compaction), rather than consumption or alteration of forb cover. Our collective findings have importance for coordinating grazing management and pollinator conservation efforts and help to distinguish how grazing practices could impact pollinator biodiversity across ecoclimatic regions.