Écologie et fonctionnement des communautés plantes-pollinisateurs en milieu urbain dense : l'exemple de la ville de Paris à travers les saisons

Urbanization is one of the main causes of biodiversity loss. Hence, organisms in the city, in particular insect pollinators, are subject to multiple constraints. In this thesis, we characterized pollinator communities and their seasonal dynamics in a dense urban landscape, the city of Paris, through empirical and standardized approaches. We first explored what distinguishes these urban communities from the rural ones, focusing on their taxonomic and functional diversity, as well as their foraging activity patterns and pollination efficiency. Then, we expanded our knowledge of Parisian pollinators, providing details on the environmental factors that determine their abundance and diversity. Finally, we investigated the dynamics of plant-pollinator interactions and their structure throughout the seasons. Despite its high density, Paris is home to relatively rich and abundant pollinator communities, which can provide efficient pollination of some plants. However, these communities are constrained by the urban environment, and undergo functional filtering. Moreover, in the city, natural seasonal dynamics are weakened both in terms of pollinator activity and functional assemblage. Flower resources play a key role in maintaining pollinator diversity, particularly through native and spontaneous flora. We provide design and management guidelines for green spaces, in order to promote biodiversity and pollination in cities.L’urbanisation est une des causes principales de l’érosion de la biodiversité. Ainsi, en ville, les organismes, et notamment les insectes pollinisateurs, sont soumis à de multiples contraintes. Au cours de cette thèse, nous avons caractérisé les communautés de pollinisateurs et leurs dynamiques saisonnières dans un paysage urbain dense, la ville de Paris, à travers des approches empiriques et standardisées. Nous avons d’abord exploré ce qui distingue ces communautés urbaines des communautés rurales, en nous intéressant à leurs diversités taxonomique et fonctionnelle, ainsi qu’à leur activité de butinage et l’efficacité de la pollinisation. Puis, nous avons approfondi la connaissance des pollinisateurs parisiens, en détaillant les facteurs environnementaux qui en déterminent l’abondance et la diversité. Enfin nous avons examiné la dynamique des interactions plantes-pollinisateurs et de leur structure au fil des saisons. Malgré sa densité, Paris abrite des communautés de pollinisateurs relativement riches et abondantes, capables d’assurer une pollinisation efficace de certaines plantes. Cependant, ces communautés sont contraintes par l’environnement urbain, et témoignent d’un filtrage fonctionnel. De plus, en ville, on assiste à l’atténuation des dynamiques saisonnières naturelles, en termes d’activité des pollinisateurs et d’assemblage fonctionnel. Les ressources florales jouent un rôle primordial dans le maintien de la diversité des pollinisateurs, en particulier grâce à la flore indigène et spontanée. Nous proposons des solutions, basées sur l’aménagement et la gestion des espaces verts, afin de promouvoir la biodiversité et la pollinisation en ville

Ecology and functioning of plant-pollinator communities in a dense urban environment : the city of Paris throughout the seasons

L’urbanisation est une des causes principales de l’érosion de la biodiversité. Ainsi, en ville, les organismes, et notamment les insectes pollinisateurs, sont soumis à de multiples contraintes. Au cours de cette thèse, nous avons caractérisé les communautés de pollinisateurs et leurs dynamiques saisonnières dans un paysage urbain dense, la ville de Paris, à travers des approches empiriques et standardisées. Nous avons d’abord exploré ce qui distingue ces communautés urbaines des communautés rurales, en nous intéressant à leurs diversités taxonomique et fonctionnelle, ainsi qu’à leur activité de butinage et l’efficacité de la pollinisation. Puis, nous avons approfondi la connaissance des pollinisateurs parisiens, en détaillant les facteurs environnementaux qui en déterminent l’abondance et la diversité. Enfin nous avons examiné la dynamique des interactions plantes-pollinisateurs et de leur structure au fil des saisons. Malgré sa densité, Paris abrite des communautés de pollinisateurs relativement riches et abondantes, capables d’assurer une pollinisation efficace de certaines plantes. Cependant, ces communautés sont contraintes par l’environnement urbain, et témoignent d’un filtrage fonctionnel. De plus, en ville, on assiste à l’atténuation des dynamiques saisonnières naturelles, en termes d’activité des pollinisateurs et d’assemblage fonctionnel. Les ressources florales jouent un rôle primordial dans le maintien de la diversité des pollinisateurs, en particulier grâce à la flore indigène et spontanée. Nous proposons des solutions, basées sur l’aménagement et la gestion des espaces verts, afin de promouvoir la biodiversité et la pollinisation en ville.Urbanization is one of the main causes of biodiversity loss. Hence, organisms in the city, in particular insect pollinators, are subject to multiple constraints. In this thesis, we characterized pollinator communities and their seasonal dynamics in a dense urban landscape, the city of Paris, through empirical and standardized approaches. We first explored what distinguishes these urban communities from the rural ones, focusing on their taxonomic and functional diversity, as well as their foraging activity patterns and pollination efficiency. Then, we expanded our knowledge of Parisian pollinators, providing details on the environmental factors that determine their abundance and diversity. Finally, we investigated the dynamics of plant-pollinator interactions and their structure throughout the seasons. Despite its high density, Paris is home to relatively rich and abundant pollinator communities, which can provide efficient pollination of some plants. However, these communities are constrained by the urban environment, and undergo functional filtering. Moreover, in the city, natural seasonal dynamics are weakened both in terms of pollinator activity and functional assemblage. Flower resources play a key role in maintaining pollinator diversity, particularly through native and spontaneous flora. We provide design and management guidelines for green spaces, in order to promote biodiversity and pollination in cities

Écologie et fonctionnement des communautés plantes-pollinisateurs en milieu urbain dense : l'exemple de la ville de Paris à travers les saisons

Urbanization is one of the main causes of biodiversity loss. Hence, organisms in the city, in particular insect pollinators, are subject to multiple constraints. In this thesis, we characterized pollinator communities and their seasonal dynamics in a dense urban landscape, the city of Paris, through empirical and standardized approaches. We first explored what distinguishes these urban communities from the rural ones, focusing on their taxonomic and functional diversity, as well as their foraging activity patterns and pollination efficiency. Then, we expanded our knowledge of Parisian pollinators, providing details on the environmental factors that determine their abundance and diversity. Finally, we investigated the dynamics of plant-pollinator interactions and their structure throughout the seasons. Despite its high density, Paris is home to relatively rich and abundant pollinator communities, which can provide efficient pollination of some plants. However, these communities are constrained by the urban environment, and undergo functional filtering. Moreover, in the city, natural seasonal dynamics are weakened both in terms of pollinator activity and functional assemblage. Flower resources play a key role in maintaining pollinator diversity, particularly through native and spontaneous flora. We provide design and management guidelines for green spaces, in order to promote biodiversity and pollination in cities.L’urbanisation est une des causes principales de l’érosion de la biodiversité. Ainsi, en ville, les organismes, et notamment les insectes pollinisateurs, sont soumis à de multiples contraintes. Au cours de cette thèse, nous avons caractérisé les communautés de pollinisateurs et leurs dynamiques saisonnières dans un paysage urbain dense, la ville de Paris, à travers des approches empiriques et standardisées. Nous avons d’abord exploré ce qui distingue ces communautés urbaines des communautés rurales, en nous intéressant à leurs diversités taxonomique et fonctionnelle, ainsi qu’à leur activité de butinage et l’efficacité de la pollinisation. Puis, nous avons approfondi la connaissance des pollinisateurs parisiens, en détaillant les facteurs environnementaux qui en déterminent l’abondance et la diversité. Enfin nous avons examiné la dynamique des interactions plantes-pollinisateurs et de leur structure au fil des saisons. Malgré sa densité, Paris abrite des communautés de pollinisateurs relativement riches et abondantes, capables d’assurer une pollinisation efficace de certaines plantes. Cependant, ces communautés sont contraintes par l’environnement urbain, et témoignent d’un filtrage fonctionnel. De plus, en ville, on assiste à l’atténuation des dynamiques saisonnières naturelles, en termes d’activité des pollinisateurs et d’assemblage fonctionnel. Les ressources florales jouent un rôle primordial dans le maintien de la diversité des pollinisateurs, en particulier grâce à la flore indigène et spontanée. Nous proposons des solutions, basées sur l’aménagement et la gestion des espaces verts, afin de promouvoir la biodiversité et la pollinisation en ville

Keeping Up with Insect Pollinators in Paris

International audienceThere is growing interest in urban pollinator communities, although they may be subject to biotic homogenization in densely artificial landscapes. Paris (France) is one of the densest cities in the world, yet over the years many insect pollinator species have been reported there. We conducted in-depth surveys of Parisian green spaces for two years, in order to improve our knowledge of these assemblages. We explored several types of green spaces, monitoring pollinators throughout their activity season. We listed 118 species of wild bees and 37 species of hoverflies, updating pre-existing lists with 32 additional species. Bee assemblages showed functional diversity with 18.5% parasitic species and 17.7% oligolectic species. We also found several bee and hoverfly species under special conservation status. Over the study period, we observed seasonal succession of species, with diversified phenological niches. The greatest taxonomic and functional diversity was found in green spaces combining several habitats with ecological management. Despite its very dense urbanism, Paris is home to diverse pollinator communities. As a result, nearly half of the wild bee species of the wider Ile-de-France administrative region can be found within the city. This highlights the need to also consider dense urban environments in insect pollinator conservation strategies

Native and exotic plants play different roles in urban pollination networks across seasons

International audienceUrban areas often host exotic plant species, whether managed or spontaneous. These plants are suspected of affecting pollinator diversity and the structure of pollination networks. However, in dense cityscapes, exotic plants also provide additional flower resources during periods of scarcity, and the consequences for the seasonal dynamics of networks still need to be investigated. For two consecutive years, we monitored monthly plant–pollinator networks in 12 green spaces in Paris, France. We focused on seasonal variations in the availability and attractiveness of flower resources, comparing native and exotic plants at both the species and community levels. We also considered their respective contributions to network properties over time (specialization and nestedness). Exotic plants provided more abundant and diverse flower resources than native plants, especially from late summer on. However, native plants received more visits and attracted more pollinator species at the community level; and during certain times of the year at the species level as well. Exotic plants were involved in more generalist interactions, increasingly so over the seasons. In addition, they contributed more to network nestedness than native plants. These results show that exotic plants are major components of plant–pollinator interactions in a dense urban landscape, even though they are less attractive than natives. They constitute a core of generalist interactions that increase nestedness and can participate in the overall stability of the network. However, most exotic species were seldom visited by insects. Pollinator communities may benefit from including more native species when managing urban green spaces

Diversity of greenspace design and management impacts pollinator communities in a densely urbanized landscape: the city of Paris, France

International audienceThe response of insect pollinator communities to increasing urbanization is shaped by landscape and local factors. But what about habitats that are already highly artificial? We investigated the drivers of pollinator diversity in a dense urban matrix, the city of Paris. We monitored insect pollinator communities monthly (March-October) for two consecutive years in 12 green spaces that differed in their management practices, focusing on four insect orders (Hymenoptera, Diptera, Lepidoptera, Coleoptera). Pollinator abundance and species richness were both positively tied to green space size and flowering plant species richness, but negatively linked to surrounding impervious surfaces. In addition, environmental features at both the local and landscape scales influenced the composition and functional diversity of wild bee communities. Indeed, small and large bees responded differently, with the occurrence of large-bodied species being impaired by the proportion of impervious surfaces but strongly enhanced by plant species richness. Also, sites with a majority of spontaneous plant species had more functionally diverse bee communities, with oligolectic species more likely to be found. These results, consistent with the literature, can guide the design and management practices of urban green spaces to promote pollinator diversity and pollination function, even in dense urban environments

Seasonal Variations of Pollinator Assemblages among Urban and Rural Habitats: A Comparative Approach Using a Standardized Plant Community

International audienceEven though urban green spaces may host a relatively high diversity of wild bees, urban environments impact the pollinator taxonomic and functional diversity in a way that is still misunderstood. Here, we provide an assessment of the taxonomic and functional composition of pollinator assemblages and their response to urbanization in the Paris region (France). We performed a spring-to-fall survey of insect pollinators in green spaces embedded in a dense urban matrix and in rural grasslands, using a plant setup standardized across sites and throughout the seasons. We compared pollinator species composition and the occurrence of bee functional traits over the two habitats. There was no difference in species richness between habitats, though urban assemblages were dominated by very abundant generalist species and displayed a lower evenness. They also included fewer brood parasitic, solitary or ground-nesting bees. Overall, bees tended to be larger in the city than in the semi-natural grasslands, and this trait exhibited seasonal variations. The urban environment filters out some life history traits of insect pollinators and alters their seasonal patterns, likely as a result of the fragmentation and scarcity of feeding and nesting resources. This could have repercussions on pollination networks and the efficiency of the pollination function

Broader phenology of pollinator activity and higher plant reproductive success in an urban habitat compared to a rural one

International audienceUrban habitat characteristics create environmental filtering of pollinator communities. They also impact pollinating insect phenology through the presence of an urban heat island and the year-round availability of floral resources provided by ornamental plants. Here, we monitored the phenology and composition of pollinating insect communities visiting replicates of an experimental plant assemblage comprising two species, with contrasting floral traits: Sinapis alba and Lotus corniculatus, whose flowering periods were artificially extended. Plant assemblage replicates were set up over two consecutive years in two different habitats: rural and densely urbanized , within the same biogeographical region (Ile-de-France region, France). The phenology of pollination activity, recorded from the beginning (early March) to the end (early November) of the season, differed between these two habitats. Several pollinator morphogroups (small wild bees, bumblebees, honeybees) were significantly more active on our plant sets in the urban habitat compared to the rural one, especially in early spring and autumn. This resulted in different overall reproductive success of the plant assemblage between the two habitats. Over the course of the season, reproductive success of S. alba was always significantly higher in the urban habitat, while reproductive success of L. corniculatus was significantly higher in the urban habitat only during early flowering. These findings suggest different phenological adaptations to the urban habitat for different groups of pollinators. Overall, results indicate that the broadened activity period of pollinating insects recorded in the urban environment could enhance the pollination function and the reproductive success of plant communities in cities

An international multicenter study exploring whether surveillance after esophageal cancer surgery impacts oncological and quality of life outcomes (ENSURE)

Objective: To determine the impact of surveillance on recurrence pattern, treatment, survival and health-related quality-of-life (HRQL) following curative-intent resection for esophageal cancer. Summary background data: Although therapies for recurrent esophageal cancer may impact survival and HRQL, surveillance protocols after primary curative treatment are varied and inconsistent, reflecting a lack of evidence. Methods: European iNvestigation of SUrveillance after Resection for Esophageal cancer was an international multicenter study of consecutive patients undergoing surgery for esophageal and esophagogastric junction cancers (2009-2015) across 20 centers (NCT03461341). Intensive surveillance (IS) was defined as annual computed tomography for 3 years postoperatively. The primary outcome measure was overall survival (OS), secondary outcomes included treatment, disease-specific survival, recurrence pattern, and HRQL. Multivariable linear, logistic, and Cox proportional hazards regression analyses were performed. Results: Four thousand six hundred eighty-two patients were studied (72.6% adenocarcinoma, 69.1% neoadjuvant therapy, 45.5% IS). At median followup 60 months, 47.5% developed recurrence, oligometastatic in 39%. IS was associated with reduced symptomatic recurrence (OR 0.17 [0.12-0.25]) and increased tumor-directed therapy (OR 2.09 [1.58-2.77]). After adjusting for confounders, no OS benefit was observed among all patients (HR 1.01 [0.89-1.13]), but OS was improved following IS for those who underwent surgery alone (HR 0.60 [0.47-0.78]) and those with lower pathological (y)pT stages (Tis-2, HR 0.72 [0.58-0.89]). IS was associated with greater anxiety ( P =0.016), but similar overall HRQL. Conclusions: IS was associated with improved oncologic outcome in select cohorts, specifically patients with early-stage disease at presentation or favorable pathological stage post neoadjuvant therapy. This may inform guideline development, and enhance shared decision-making, at a time when therapeutic options for recurrence are expanding