Narrow niches, narrow ranges: Linking floral specialization to geographic vulnerability in bees

Diet breadth and geographic range size are both important life history traits that influence species’ responses to environmental change. Species with both restricted ranges and narrow diets are predicted to face elevated extinction risk, but whether these traits are correlated in bees remains poorly understood. Clarifying whether these traits covary, thereby increasing risk for a smaller group of species, or operate independently, thereby spreading risk more evenly, would help target conservation efforts. In this study, we combined pollen-use data from natural history collections with global occurrence records to analyze diet breadth and range size in 633 bee species from six families. Across bees, range size and diet breadth were positively correlated, with diet specialists tending to occupy smaller ranges. This relationship was significant within families Andrenidae, Apidae, Colletidae, and Megachilidae, but not within Halictidae or Melittidae. These results suggest that in several bee families, dietary specialization and small range size may jointly contribute to increased vulnerability, potentially meriting conservation prioritization for specialist taxa in these families. Our findings also underscore the importance of trait-based approaches for assessing extinction risk and highlight the high value of natural history data in evaluating patterns of vulnerability among pollinators.