A global synthesis of local and landscape effects on native bee pollinators across heterogeneous agricultural systems

Background/Question/Methods

Crop pollination by bees is an essential ecosystem service that may be affected both by local farm management and the surrounding landscape context.  Our ability to understand and predict relative contributions of local and landscape attributes to pollinators across heterogeneous landscapes remains limited.  We applied a quantitative, mechanistic model to predict relative abundance of wild pollinators (bees) based on foraging distances and landscape composition data that were coded to capture differences in nesting and floral resources in 39 studies spanning 14 countries on 23 different crops.  Using mixed model analysis in a model selection framework, we then tested the relative importance of landscape composition (outputs from the quantitative mechanistic model), landscape configuration (patch shape, inter-patch connectivity, and habitat aggregation), and local farm management (organic versus conventional farming and vegetative diversity on a farm). 

Results/Conclusions

The strongest predictors of pollinators globally were local farming practices in combination with landscape composition, but these local-landscape factors may interact.  Bee abundance and richness strongly increased on organic farms with highly diversified on-farm vegetation and in landscapes supporting greater amounts of bee-friendly habitat.  The extent to which landscape-level habitat composition benefited bee communities, however, was estimated to be greater on conventional farms with low vegetative diversity.  Although social bees were greatly affected by landscape aspects in combination with local farm management practices, solitary bees were more strongly affected by local farming practices.  Overall landscape configuration effects were weak.  Among configuration metrics, variation in inter-patch distance of habitats most influenced bee abundance.  Our synthesis reveals that persistence of pollinators in agricultural systems globally will depend not only upon maintaining sufficient amounts of high quality habitats surrounding farms, but also on local management practices that may offset losses that often occur in landscapes dominated by intensive monoculture agriculture.