Plant-hummingbird interaction networks in urban areas: Generalization and the importance of trees with specialized flowers as a nectar resource for pollinator conservation

Abstract Cities harbour considerable biodiversity and there has been an increased concern about the conservation of pollinators in urban environments. Here, we evaluated how urbanization affects plant-hummingbird interactions at two spatial scales. First, in a medium-sized city from southeastern Brazil (>600,000 inhabitants), we contrasted interaction networks from urban and natural areas, and used artificial nectar feeder stations to evaluate changes in the composition of hummingbird assemblages across an urbanization gradient. Second, we compiled data on six urban plant-hummingbird interaction networks from south and southeastern Brazil to identify the characteristics associated with the most important plants. Locally, urbanization affected hummingbird communities by promoting higher generalization and dominance by more aggressive hummingbirds. Notably, specialized long-billed hermits were absent both in the urban interaction network and at feeder stations from more urbanized areas. Across networks, trees were more important for hummingbirds than shrubs/herbs as were specialized ornithophilous flowers in relation to non-ornithophilous flowers. Plant origin (native or exotic) did not matter. Our results indicate that urban plant-hummingbird communities are organized differently than their counterparts from natural areas, which usually feature key hermits and few trees. Since hermits provide important pollination services, especially for specialized ornithophilous plants, initiatives such as green corridors and preference for native plants with specialized hummingbird-pollinated flowers in urban landscaping may contribute to community restoration and ecosystem functioning.