Soil sand content is a driving force in structuring bee communities

Floral and nesting resources are two major components of habitat specialization that drive patterns of bee distribution. However, nesting resources are understudied in comparison to floral resources. Sand preference is seen as a community-wide nesting trait for bee species and numerous species are considered sand specialists. We aimed to test how soil sand content and floral resource availability interact to affect patterns of bee distribution and whether sand specialist bees predominantly occur in sandy habitats. We set up a controlled field experiment in prairies in Minnesota, USA across three classes of soil sand content (N = 28 plots) using a focal prairie plant species (Dalea purpurea) that attracts a wide range of bee species and can grow in different soil types. We identified four key results: 1) soil sand content, not floral resource availability, affected patterns of bee distribution; 2) contrary to expected, sandier sites did not host the highest bee diversity; 3) there was clear evidence of sand specialization for select bee species, but sand specialists were associated with both moderate and high amounts of sand rather than extremely sandy areas; and 4) the proportion of abundance of sand specialists increased as the soil sand content within discrete pockets increased, even in areas with average values of low sand content. Our findings highlight that soil sand content can be more important than floral resources in driving patterns of bee distribution, specifically sand specialists. Therefore, factoring soil properties into bee conservation decisions may help support specialists and rare bee communities.