Exploring the impact of local floral quality and land use on bumble bee communities: Insights into common and at-risk species

Human-mediated land-use change and habitat degradation due to row-crop agriculture negatively impact bumble bee communities, but declines are not uniform across species. This study investigates how local floral variables and surrounding land use affect bumble bee abundance and species richness in Illinois, focusing on both common and rare species. We hypothesized that local factors, such as flower abundance and the Floristic Quality Index (FQI), would positively correlate with bumble bee richness and abundance, while higher agricultural intensity would negatively influence these metrics. Over three years, we sampled bumble bee communities at eleven sites, assessing local floral quality and surrounding land use. Our findings indicated that the FQI was a significant positive predictor of overall bumble bee abundance, common bumble bee abundance, and bumble bee community richness. Additionally, FQI was a marginally significant predictor of the abundance of rare species, emphasizing the importance of maintaining high-quality floral habitats. At the landscape level, we found that common bumble bee species had a significant positive association with various degrees of human development, whereas rare bumble bee species showed a strong positive association with increased areas of surrounding natural habitats. These findings suggest that conservation strategies for bumble bees should focus on increasing native floral diversity. Additionally, to support rare species, improving the quality of natural areas at the landscape level is crucial. By integrating local and landscape-level factors into conservation plans, more nuanced approaches to conservation can be developed that address the specific needs of bumble bee species of greatest conservation need. • FQI (Floristic Quality Index) increased bumble bee abundance and richness. • FQI was positively associated with common and rare bumble bee abundances. • Common and rare species were differentially affected by surrounding land-use. • Urban development correlated with an increased abundance of common species. • Surrounding natural areas increased the abundance of rare species.