Urbanization influences the structure of plant–insect pollination networks through changes in pollinator species richness

Abstract

Urbanization promotes changes in the diversity of plants and pollinators which, in turn, result in novel ecological interaction networks that can be structurally different from those of natural habitats. Using published data from 32 studies across 18 ecoregions, we analyzed plant–insect networks from natural habitats and landscapes (‘natural networks’), natural habitats surrounded by urban matrices (‘natural–urban networks’), and urban networks in urbanized landscapes (‘urban networks’) to investigate the direct and indirect effects of urbanization on the structure of these networks. Through path analyses, we evaluate the effects of habitat type, proportion of exotic plant species, and pollinator richness on network connectance, nestedness, and modularity, while controlling for plant richness and ecoregion. We found that the effects of urbanization on network structure are primarily indirect, mediated by the decrease in pollinator richness, rather than directly or via the proportion of exotic plant species, underscoring the critical role of maintaining diverse pollinator populations in urban areas to sustain ecological network integrity. Our study highlights the need to consider direct and indirect effects when evaluating how urbanization affects plant–pollinator networks. This approach is especially important for conservation strategies aiming to mitigate the impact of urban development on plant–pollinator interactions.