Urban densification and vegetation composition reshape ecological networks across trophic layers

Kilian Perrelet , Sebastian Ruile, Merin Reji Chacko , Joan Casanelles-Abella, Bertrand Fournier, Marco Moretti

Urban densification reshapes biodiversity, yet its effects on ecological networks across trophic levels remain unclear. Using a metaweb approach, we reconstructed bipartite, multitrophic, and combined food webs across 60 urban green spaces along gradients of urban densification and vegetation complexity. Densification reduced taxonomic and interaction richness, promoted interaction generalization, and homogenized networks. Its effects depended on network type, altering connectance, nestedness, and modularity differently in bipartite and multitrophic networks while increasing dependencies among trophic layers, ultimately reducing the robustness of combined food webs. Higher plant richness partly mitigated these effects by promoting interaction diversity, trophic specialization, and robustness, although responses varied across network types. Non-native plants also induced network-specific shifts, favoring highly connected consumers in bipartite networks while leaving overall structure largely unchanged. Our results show that urban density and vegetation composition jointly restructure ecological networks in a network-type-dependent manner, and that single-guild perspectives may misrepresent ecosystem-level responses in cities.