The decades-long recovery of nocturnal bees in logged forests is counteracted by broad resource range and reliance on pioneers

Ugo Mendes Diniz , Juan Ernesto Guevara-Andino, Gunnar Brehm, Sara D. Leonhardt, Alexander Keller

Nocturnal bees are elusive pollinators for which little and fragmented evidence of their dietary breadth is available. Moreover, despite their assumed relevance as pollinators of tropical plants, there is no information on how nocturnal bees respond to the loss of suitable habitats and forest succession. Here, we investigated the recovery of Megalopta bees, a prominent group of nocturnal pollinators, within a forest regeneration chronosequence in northwestern Ecuador. By employing next-generation sequencing on pollen loads, we also assessed the group's resource use and the recovery of interaction networks. Megalopta bees showed low resistance and delayed recovery, as abundance had not recovered to pre-disturbance forest levels after 38 years of succession. Stratification was the strongest driver of recovery, with bees strongly associated with old-growth canopies. In contrast, their diet was broad, encompassing more than 120 plant species. The bulk of pollen loads was, however, constituted by pioneer species, while primary forest trees and plants with specialized nocturnal pollination systems were less represented. The use of diverse resources not necessarily tied to old-growth forests thus contributed to network stability across succession. We provide the first molecular assessment of the diet of a dominant group of nocturnal bees, expanding the understanding of their consumption of floral resources. While dietary breadth may buffer the adverse effects of disturbance on the group, their dependence on the canopies of old, structurally complex forests, likely for nesting, suggests that nocturnal bees are quite vulnerable to the loss of large portions of primary habitats.