Contributions of phenological groups of wild bees as an indicator of food availability in urban wastelands

Abstract Protection and increasing of biodiversity in urban areas should be a priority for urban authorities, managers of green areas, and the society. This objective can be reached by proper shaping of vegetation structure in green spaces, including urban wastelands, on the basis of e.g. investigation of relations between bees and their food plants. We evaluated the attractiveness of vegetation to the Apiformes, as an indicator of food availability in wastelands, in the city of Bydgoszcz and its suburbs. In respect of species richness and abundance, early-spring bees (emergence in March-April) and spring bees (emergence in May) prevailed in suburban habitats. In contrast, in urban wastelands, summer species of bees (emergence in June) were the richest and most abundant. This was linked with analogous differences in species richness of bee food plants starting to flower in those periods, and various plant life-forms played important roles in individual phenological periods. In the case of early-spring and spring bee species, the differences concerned primarily polylectic and cleptoparasitic bees, which prevailed in suburban habitats. Polylectic bees that emerged in summer were more abundant in urban habitats. No such a relationship was observed for oligolectic species, whose occurrence depends on the presence of a narrow group of bee food plant species, irrespective of their location and degree of human disturbance. We also found that trees and shrubs were major sources of food for the dominant bee species in early spring and spring. Among native plants, the most important role was played by apophytes (i.e. native plants typically growing on disturbed land) starting to flower in spring. Our results can be used by managers of urban landscape to shape urban vegetation so that it provides a continuous supply of food for bees and other pollinating insects.