Assessing ecological interactions in urban areas using citizen science data: Insights from hummingbird-plant meta-networks in a tropical megacity

Urbanization is one of the most intensive threats to biodiversity worldwide. The rapid sprawl of urban settings often comprises a drastic landscape transformation due to the replacement of natural vegetation by impervious surfaces. However, cities can serve as critical refuges for some native fauna, particularly for pollinators. Here we used citizen data to contrast the structure of hummingbird-plant meta-networks across different greenspaces (natural protected areas, urban parks, urban gardens and street trees areas) in a tropical megacity. We compiled hummingbird-plant visitation records in Mexico City available in two citizen science resources: iNaturalist and eBird. We first determined whether the retrieved dataset was representative to estimate network metrics by calculating sample coverage and estimating species richness in different greenspaces. Then, we characterized network structure and plant importance for network organization according to plant origin, life form and pollination syndrome. We recorded 17 hummingbirds visiting 84 plant species, encompassing a total of 742 interactions. Natural protected areas and urban parks showed a higher richness of hummingbirds and plants. All networks had low levels of connectance, specialization, and nestedness. Modularity was significant across all networks with higher values in natural protected areas and urban gardens. Native and introduced plant species showed a similar contribution to network organization. Non-ornithophilous plants were most important in natural protected areas, while tree species were most important in street trees greenspaces. Our results provide evidence of generalization of hummingbird-plant networks in urban areas. Introduced species and nonornithophilous plants were equally important for hummingbirds, suggesting an integration of alien plants with no specialized bird pollination traits into ecological networks in urban scenarios. Promoting conservation initiatives as pollinator gardens with key native species for hummingbirds across the city could contribute to the functional connectivity and restoration of ecological interactions in cities.