Rare species account for much of biodiversity, but are difficult to study due to inadequate sampling. Agricultural landscapes have been shown to support diverse and abundant bee communities; however the extent to which they support regionally rare species is unknown. Here we compare species richness and composition of rare bees from agricultural and natural habitats within a unique ecosystem where two native plant species are grown as important commercial crops. We defined rare species as those occurring in the lowest quartile of frequency in an independent dataset of 28,934 museum collection records from the northeastern USA. We applied these rarity designations to bee communities collected from 32 agricultural sites (cranberry and blueberry) and 40 natural sites (meadows and forest), all within the same larger oak-pine forest ecosystem. First, we compared richness of rare bee species among the four habitats using site-species accumulation curves. Second, we compared the composition of all species and rare species using a PERMANOVA analysis. Finally, we qualitatively compared the phenologies of the rare species unique to each habitat type with the blooming times of plants in the other habitats to determine whether bees’ apparent habitat affinities may be explained by phenology.
Our dataset included 8959 specimens of 176 species and 29 rare species. Rare species richness was highest in the meadow sites (17) followed by forest (14), cranberry (8) and blueberry (3). We found that overall community composition did differ between habitat types (R-squared value = .086, p value = .003). However, rare bee composition was not detectably different, possibly because rare species were sparsely distributed across sites. Meadow habitat had the most unique rare species (rare species that were not found in other habitat types) (8) followed by forest (5), cranberry (4), and blueberry (1). Of the 13 species unique to natural habitats, 2 had phenologies that did not coincide at all with the blooming times of cranberry and blueberry, suggesting that these species cannot use agricultural for phenological reasons. Native crops do support rare species, but these species are a small subset from the regional pool. Natural areas are required in order to support all of the rare species in the region.