Modifications of the plant-pollinator network structure and species' roles along a gradient of urbanization

This is the preprint for the article titled "Modifications of the plant-pollinator network structure and species’ roles along a gradient of urbanization".

Abstract

1. Urbanization may significantly alter the abundance, composition and phenology of natural communities of plants and pollinators. However, how such alterations eventually affect the structure of plant-pollinator interaction networks is still poorly known.

2. We examined changes in the structure of plant-pollinator networks in 12 sites along an urbanization gradient in a metropolis in Northern France, along which a phenological shift has been previously observed for flowering plants but not for pollinators. We used classic network metrics in combination with more detailed methodologies to identify changes in the network structure and modifications in species clustering and species’ roles through urban classes and time. We also evaluated the temporal trajectories of α- and β-diversity of species and interactions along the gradient.

3. Classic network metrics showed limited spatio-temporal variation in the overall structure. Finer-scale analyses showed that generalist species with long phenologies were the most central and played key roles in defining the composition of cohesive groups of interacting species in all networks. However, species’ roles and interaction diversity showed different temporal trajectories among the urbanization classes, especially early in the season. These differences are likely partially driven by the advanced flowering peak observed in sites at high urbanization.

4. Synthesis. Our findings evidence an alteration of the structure of plant-pollinator networks along an urbanization gradient. Species with long phenologies and high numbers of interacting partners are important in defining the network structure. However, species’ roles and interaction diversity respond differently to increasing urbanization, probably partially in response to changes in plant flowering phenology.