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Anthropogenic activities in urban ecosystems induce a myriad of environmental changes compared with adjacent rural areas. These environmental changes can be seen as series of abiotic and biotic selection filters affecting the distribution of plant species. What are the attributes of plant species that compose urban communities, compared with rural communities, as related to their ecological affinities (e.g., to temperature, humidity), and reproductive traits (e.g., entomophily, autogamy, floral morphology)? Using a floristic dataset from a citizen science project recording plant species growing spontaneously in the streets, we analyzed the distribution of species according to their ecological requirements and reproductive traits along an urbanization gradient in the Parisian region. We developed an original floral and pollinator typology composed of five floral and four pollinator morphotypes. The proportion of impervious areas, used as a proxy of urbanization, was measured at different spatial scales, to reveal at which spatial scales urbanization is selecting plant traits. We found significant differences in plant communities along the urbanization gradient. As expected with the warmer and drier conditions of urban areas, species with higher affinities to higher temperature, light and nutrient soil content, and lower atmospheric moisture were over-represented in urban plant communities. Interestingly, all of the significant changes in plant abiotical affinities were the most pronounced at the largest scale of analysis (1,000 m buffer radius), probably because the specific urban conditions are more pronounced when they occur on a large surface. The proportion of autogamous, self-compatible, and nonentomophilous species was significantly higher in urban plant communities, strongly suggesting a lower abundance or efficiency of the pollinating fauna in urban environments. Last, among insect-pollinated species, those with relatively long and narrow tubular corollas were disadvantaged in urban areas, possibly resulting from a reduction in pollinator abundance particularly affecting specialized plant-pollinator interactions., Competing Interests: None declared.

Urbanisation, associated with habitat fragmentation, affects pollinator communities and insect foraging behaviour. These biotic changes are likely to select for modified traits in insect-pollinated plants from urban populations compared to rural populations. To test this hypothesis, we conducted an experiment involving four plant species commonly found in both urban and rural landscapes of the Île-de-France region (France): Cymbalaria muralis, Geranium robertianum, Geum urbanum and Prunella vulgaris. The four species were grown in four urban and four rural experimental sites in 2015. For each species and each experimental site, plants were grown from seeds collected in five urban and five rural locations. During flowering, we observed flower production and insect-flower interactions during 14 weeks and tested for the effects of experimental site location and plant origin on flower production and on the number of floral visits. The study species had various flower morphology and hence were visited by different floral visitors. The effect of experimental sites and seed origin also varied among study species. We found that (1) insect visits on P. vulgaris were more frequent in rural than in urban sites; (2) for C. muralis, the slope relating the number of pollinator visits to the number of flowers per individual was steeper in urban versus rural sites, suggesting a greater benefit in allocating resources to flower production in urban conditions; (3) as a likely consequence, C. muralis tended to produce more flowers in plants from urban versus rural origin.