Urbanization drives an early spring for plants but not for pollinators

This is the preprint for the article titled "Urbanization drives an early spring for plants but not for pollinators".

Abstract

Urbanization is one of the major threats to wild plants and pollinators, and its global increase urges a better understanding of the mechanism driving its negative impact. Urban warming and altered local environmental conditions have the potential to affect the timing of flowering and of pollinator activity. While previous evidence showed that plant phenology tends to advance in urban areas, little is known about its effects on pollinator phenology and no study has yet explored the potential mismatch of plant-pollinator interactions. In this study we simultaneously assess the response of the timing of flowering of native plants and of the flight period of wild pollinators to increased urbanization. We collected data from 12 sites along an urbanization gradient in Northern France, a region under strong anthropogenic pressure. Overall, we recorded more than 70 plant species, and we sampled more than 4,300 wild bees and hoverflies belonging to 154 species. Plant blooming showed a strong response to urbanization at the community level with a striking advancement of the flowering peak in sites at high urbanization. On the contrary, pollinator communities did not show any clear shift of their flight phenology along the gradient, neither regarding abundance nor diversity. Our results indicate that phenologies of plant and pollinator communities can respond differently along the same urbanization gradient. These asymmetric responses can drive modifications in the structure of plant-pollinator networks, and potentially negatively affect the fitness of both mutualistic partners.