The effects of human-driven landscape disturbance on wild bee communities and plant-bee networks across southern Manitoba, Canada
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Landscape disturbance caused by human activities like large-scale cropping and urbanization is one of the main drivers of wild bee declines and changes to plant-pollinator networks worldwide. Factors such as land cover diversity and fragmentation can also influence bee communities and networks, but published effects are mixed and often depend on location, community composition, and scale of disturbance. I investigated the effects of local and landscape level disturbance on bee communities and plant-bee networks across southern Manitoba, Canada, with the goal of informing policies aimed at conserving wild bee populations and network functionality. I collected 21,000 bees over two years using coloured pan traps and blue vane traps (for community analyses) and 2,189 using aerial nets (for network analyses). Using linear modelling, I found that crop cover reduced bee abundance and richness, and negatively affected network stability, indicating that greater amounts of crop cover in the landscape have widespread negative effects on both bees and networks. Conversely, fragmentation and land cover diversity benefitted bee abundance, richness, and community functional dispersion in most ecoregions, and enhanced network size and stability. This suggests that areas with greater amounts of edge, as well as a diverse array of land cover types, can benefit bees and networks. Finally, I found that the number of introduced plant species at the local scale enhanced bee community functional dispersion without negative effects on bee abundance or richness, suggesting that introduced plants in field margins help rather than hurt bee communities where native plants have been lost due to disturbance. Extensively removing introduced plant species from field margins should be reconsidered since these species help to support wild bee communities in disturbed areas. Land management policies promoting more extensive field edges and increasing land cover diversity are needed to maintain an abundant and diverse assemblage of bees and to enhance plant-bee network size and stability.
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