\received DD MMMM YYYY \acceptedDD MMMM YYYY 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, sand preference is seen as a community-wide trait for bee species 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. We also designed the study to evaluate whether sand specialist bees predominantly occur in sandy habitats. We set up a controlled field experiment 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 diversity of bee species; 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 properties, specifically soil sand content, can be more important than floral resources 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. Sandy areas and places with high soil heterogeneity should be prioritized for conservation.

Aim 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, sand preference is seen as a community-wide trait for bee species 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. We also designed the study to evaluate whether sand specialist bees predominantly occur in sandy habitats. Location Midwestern prairies in Minnesota, USA. Methods We set up a controlled field experiment 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. Results 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 diversity of bee species; 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. Main Conclusion Our findings highlight that soil properties, specifically soil sand content, can be more important than floral resources 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. Sandy areas and places with high soil heterogeneity should be prioritized for conservation.

Emergence traps have increasingly been used to study ground nesting bees. They offer an advantage over other methods, such as netting or passive traps, because they can directly measure ground nesting bees at a landscape scale. However, emergence trapping for ground nesting bees has limitations, including low catch rates and data that is difficult to interpret. For example, emergence traps catch a combination of actively nesting bees, newly emerging bees from nests provisioned the previous year, overwintering bees, and incidental bees, such as non-ground-nesting species or bees that were simply sleeping on vegetation. Further, a single emergence trap can capture many specimens from a single nest due to the presence of workers, newly emerging reproductives (gynes), or multiple siblings from a nest provisioned the previous year. Due to these factors, a thorough knowledge of the life history of bee species collected is necessary to accurately filter and interpret the data. Here, we provide methods to determine whether bee specimens caught from emergence traps came from nests. Using a combination of trap data, life-history characters, and estimates of bee age, we classify bees as newly emerging, active nests, or incidentally caught. This will allow researchers to reduce the risk of spurious inferences that may over- or under-estimate bee nesting. Many areas of future research remain, particularly studies on the efficacy of emergence traps for ground-nesting bee research as well as a glaring need to better document the life-history of many bee species.   Abstract content goes here