COS 223-4 - Pollen quality as a potential driver for bumble bee abundance and diversity in restored prairies

Abstract: Many bee populations are declining globally, in large part due to habitat loss and the resulting nutritional shortages. Restored prairies have been shown to support a greater abundance and diversity of bumble bees than non-restored old agricultural fields, in part due to increased floral resource abundance. However, floral resource abundance does not appear to be the only driver of bumble bee abundance. Given bumble bees’ development and survival depends upon pollen with a high nutritional value (i.e., a high Protein:Lipid ratio), we expect nutritional quality may also play an important role in bumble bee abundance and diversity in restored prairies. However, nutritional quality of the floral resources in restored prairies is largely unknown. Understanding the community-level nutritional quality of the floral resources would aid our understanding of the potential mechanisms for variation in local bumble bee abundance and diversity in restored prairies. Here we ask, do prairie restorations with high community-level Protein:Lipid (P:L) pollen have more abundant and diverse bumble bee populations than sites with a low community P:L pollen? To answer this question, we collected floral resource and bumble bee data during the summers of 2019-2022. Pollen from common herbaceous prairie species was collected and macronutrient assays were completed in 2021 and 2022. Community-level pollen nutritional quality is an average P:L of each flowering species found at a site and weighted by its abundance. We compared sites where we had over 80% of P:L ratios for the species observed (n=20; p-value: 0.056; r-squared: 0.25). A linear model with pollen nutritional quality and floral resource abundance explained 53% of variation in bumble bee abundance (p-value: 0.01). Bumble bee diversity does not appear to be a function of community pollen nutritional quality.