Time Is Not Everything: Spatial Segregation of Nests in Nocturnal and Diurnal Carpenter Bees

ABSTRACT Evolutionary transitions to nocturnality in bees are rare and recent, occurring independently across several families, with activity ranging from crepuscular to strictly nocturnal. Although the “enemy‐free” and “competition‐free space” hypotheses are often suggested as drivers, these remain little explored in bees. In sympatric diurnal and nocturnal carpenter bees, we show that in addition to temporal partitioning, the truly nocturnal bee Xylocopa tranquebarica and its diurnal relatives X. tenuiscapa and X. leucothorax spatially segregate by differential preference of plant species for nesting. Xylocopa tranquebarica and X. leucothorax are nesting generalists, while X. tenuiscapa is an extreme specialist on the tree, Syzygium cumini in our study site. The hardwood of S. cumini may protect X. tenuiscapa from bird predators; avian predation rates were highest in the nocturnal X. tranquebarica and absent in X. tenuiscapa . The presence of X. tranquebarica females in the nest during the day potentially deters bird predators and helps guard developing brood. Our findings suggest that nocturnality in this species is likely maintained by predation pressure and competition for nesting sites, rather than by foraging advantages. In fact, previous work in the same site showed that nocturnality in X. tranquebarica is associated with reduced reproductive fitness due to limited nocturnal floral resources, compared to two sympatric diurnal congeners. Thus, spatial segregation of nesting sites and brood predation risk may contribute to maintaining the diurnal–nocturnal niche axis in these sympatric bees.