Bumble bee species distributions and habitat associations in the Midwestern USA, a region of declining diversity

Abstract

Bumble bees ( Bombus spp.) are important pollinators, yet rapidly declining globally. In North America some species are thriving while others are nearing extinction. Recognizing subtle differences in species’ biology and responses to environmental factors is required to illuminate key threats and to understand their different population trajectories. We intensively surveyed bumble bees in Ohio, USA, along the receding southern boundary of many species’ ranges, to evaluate current conservation status of the state’s species. In 318 90-min field surveys across two consecutive years we observed 23,324 bumble bees of 10 species visiting 170 plant species. Habitat, landscape, latitude, and their interactions significantly influenced bumble bee abundance, species richness, and community composition during peak season. Sites planted with flowers yielded more bumble bee individuals and species than did sites not planted with bee food plants. Bombus impatiens, B. griseocollis , and B. bimaculatus comprised 93% of all observations. Their abundances all peaked in habitats planted with wildflowers, but there were species-specific responses to local and landscape factors. Three less common species ( B. fervidus, B. vagans , and B. perplexus ) were more likely to be found in forested landscapes, particularly in the northeastern portion of the state. Bombus perplexus was also affiliated with planted urban wildflower patches. These results provide a strong starting point for future monitoring and conservation intervention that targets less common species. A quantitative synthesis of detailed state-level and regional datasets would allow additional insight into broad scale patterns of diversity in bumble bee communities and species conservation trajectories.

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