Soil sand content is a driving force in structuring bee communities

Abstract Floral and nesting resources are two major components of habitat specialization that drive patterns of bee distribution. However, nesting resources are largely understudied in comparison to floral resources. For nesting, bees are generally thought to prefer nesting in sandy soils, and numerous species are considered sand specialists. With little empirical evidence to date, 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 carefully designed observational study 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 three key results: (1) soil sand content, not floral resource availability, affected patterns of bee distribution; (2) contrary to expectations, sandier sites did not host the highest diversity of bee species; and (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. Our findings highlight that soil properties, specifically soil sand content, can be important in driving patterns of bee distribution, specifically sand specialists. Therefore, not factoring soil properties into bee conservation and restoration decisions may limit our effectiveness and ability to support habitat specialists and rarer bee communities.