La diversité des interactions plantes-pollinisateurs : Un pré-requis indispensable à la stabilité des écosystèmes

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Functional Diversity of Plant–Pollinator Interaction Webs Enhances the Persistence of Plant Communities

Pollination is exclusively or mainly animal mediated for 70% to 90% of angiosperm species. Thus, pollinators provide an essential ecosystem service to humankind. However, the impact of human-induced biodiversity loss on the functioning of plant–pollinator interactions has not been tested experimentally. To understand how plant communities respond to diversity changes in their pollinating fauna, we manipulated the functional diversity of both plants and pollinators under natural conditions. Increasing the functional diversity of both plants and pollinators led to the recruitment of more diverse plant communities. After two years the plant communities pollinated by the most functionally diverse pollinator assemblage contained about 50% more plant species than did plant communities pollinated by less-diverse pollinator assemblages. Moreover, the positive effect of functional diversity was explained by a complementarity between functional groups of pollinators and plants. Thus, the functional diversity of pollination networks may be critical to ecosystem sustainability

Cycles de vie, variabilite morphologique et polymorphisme pollinique chez quelques endemiques pyreneennes

INIST T 77628 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Etude multi-échelles de l effet des perturbations anthropiques sur l écologie des insectes pollinisateurs (du comportement individuel à la structure des communautés)

Les insectes pollinisateurs sont responsables de la reproduction de plus de 80% des plantes sauvages et de plus de 70% des espèces cultivées à travers le monde. Pourtant, depuis quelques années, les populations d insectes pollinisateurs sont en déclin, faisant craindre une crise de pollinisation. La perte d habitats naturels est considérée comme une des causes majeures de ce déclin des pollinisateurs. Cette perte d habitats se fait notamment au profit de l accroissement de l urbanisation. Cette artificialisation des milieux a des effets potentiels sur l abondance et la composition en espèces des communautés de pollinisateurs, sur leurs interactions avec les plantes à fleurs et sur les comportements individuels de butinage. Dans cette thèse, nous avons cherché dans un premier temps à comprendre comment les perturbations d origines anthropiques pouvaient affecter le comportement de butinage des pollinisateurs à l échelle locale. Puis en se plaçant à l échelle du paysage, nous avons étudié les modifications de la structure du réseau d interactions plantes-pollinisateurs et de la structure de la communauté d insectes floricoles le long d un gradient d accroissement des perturbations anthropiques (ici l urbanisation). Nous avons montré que la chute de la densité de Bombus terrestris butinant à l échelle d un patch influençait les relations de compétitions entre congénères, donc leur comportement. Ceux-ci montraient à faible densité un comportement moins spécialiste envers l espèce de plante connue résultant en un succès reproducteur potentiel plus faible pour cette espèce. A l échelle du paysage, , nous avons réalisé une approche expérimentale menée en région Ile-de-France qui a montré que l accroissement de l urbanisation entraîne une diminution du nombre d interactions entre plantes et pollinisateurs sauvages. Elle entraîne également une chute de l abondance d individus et de la richesse en espèces dans les communautés d insectes floricoles. Les insectes spécialistes, comme les abeilles solitaires ou les syrphes, semblent davantage impactés par l urbanisation que les espèces généralistes de plus grande taille comme les bourdons. Le principal élément paysager impactant les insectes floricoles est l accroissement des surfaces imperméables. Enfin, ces variations d abondance et de richesse spécifique des pollinisateurs peuvent potentiellement modifier le succès reproducteur et donc la pérennité des communautés végétales. Cette thèse illustre à quel point les perturbations d origines anthropiques affectent les insectes pollinisateurs à toutes les échelles d intégration de leur écologie, du comportement individuel à la structure des communautés. Dans le contexte actuel d anthropisation croissante des milieux, des mesures de restauration des continuités écologiques, notamment dans les milieux urbains via l augmentation des surfaces fleuries ou l implantation de toits verts pourraient être des mesures de conservation utiles dans le but de préserver le service écologique de pollinisation.More than 80% of wild plants and 70% of crops depend on pollinators for reproduction and food production. However, there is growing evidences that wild pollinators are declining worldwide. One of the major causes of this decline is the expansion of agricultural areas and urbanisation at the cost of natural habitats. This loss of natural habitats is likely to impact pollinator species abundance and richness, and thus the structure of pollinator communities, their interactions with flowering plants and the individual behaviour of foraging insects. In this thesis, we analyzed how anthropogenic disturbances may modify pollinator foraging behaviour, at the patch scale. Then, at the landscape scale, we tested if increasing levels of urbanisation can impact plant-pollinator interaction webs and on flower-visitor community composition and structure. At the patch scale, we found that the foraging behaviour of Bombus terrestris individuals was modified by the loss of conspecifics density. When foraging on an experimental plant community at low conspecific density, fewer visits were carried out on the most-well known plant species, resulting in a lower potential reproductive success for this plant. At the landscape scale, increased levels of urbanisation also led to a decrease in the number of interactions between wild pollinators and plants of an experimental plant community. The diversity and density of the wild pollinating fauna also decreased along this urbanisation gradient located in the Île-de-France region (France). In particular, small specialists insects such as Syrphidae and solitary bees were more impacted by urbanisation than large generalist species such as bumblebees. Finally, these variations had an impact on the reproductive success of the experimental plant community. This work illustrates how anthropogenic perturbations affect pollinating insects in several aspects of their ecology, from their foraging behaviour to the structure of their communities. In a global context characterised by incresing losses of natural habitats at the expense of urbanisation, these results should help designing conservation practices to promote ecological continuities in urban habitats, through the increase of flowered and green roof surfaces. Overall, these measures might help preserving pollinating faunas that will sustain the pollination ecological service.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

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

Global changes: an emerging trend in bee biology

International audienc

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

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

La ville un désert pour les abeilles sauvages ?

International audienceABSTRACT: Urban ecosystems are expanding worldwide and are often considered as biological deserts. However, environmentally‑friendly management practices may promote the maintenance of urban communities. Such is the case for wild bees (super family Apoideae) with an increasing number of studies reporting relatively diverse bee assemblages in densely urbanized habitats. Here, we report some examples found in the bibliography of cities harbouring relatively diverse bee assemblages, although different methods were used to sample wild bees. We also provide new data concerning the wild bee fauna in the city of Paris (France). During a two‑year field campaign carried out in 7 locations in downtown Paris, we captured 360 individuals belonging to 51 species. This raises the bee species richness in Paris to 67 species. Although this assemblage only represents 6.9 %of the French bee fauna and shows characteristics of a depauperate community (low abundance of parasitic species, dominance of the Halictidae family), some of the Parisian localities sampled exhibit relatively important species richness. This diversity should be preserved given the global pollination crisis and the current context of increasing urbanization. However, emerging management practices in urban environments, such as massive introductions of domesticated honeybee colonies (more than 700 hives are currently established in downtown Paris) could negatively impact on these communities of urban pollinators.RESUME : Les milieux urbains sont en expansion constante et sont parfois considérés comme des déserts de bio‑ diversité. Pourtant, une certaine biodiversité existe en ville et les pratiques de gestion émergentes dans les milieux urbains peuvent aider à son maintien. C'est notamment le cas pour les abeilles sauvages (super‑famille des Apoidés Apiformes) où des études de plus en plus nombreuses montrent qu'une biodiversité non négligeable d'abeilles peut être présente dans les centres urbains denses. Nous relayons ici les résultats de certains de ces articles qui, avec des méthodes et des intensités de piégeages différents, montrent tous que les villes peuvent héberger des assemblages relativement diversifiés d'abeilles sauvages. Nous apportons également de nouvelles données sur la faune d'abeilles de Paris intra‑muros. Lors d'une campagne de terrain de deux ans dans sept localités de Paris nous avons capturé 360 spécimens d'abeilles sauvages appartenant à 51 espèces différentes. Cette nouvelle campagne porte la richesse spécifique de Paris intramuros à 67 espèces. Bien que cet assemblage ne regroupe que 6.9 % des espèces de la faune Française et montre des caractéristiques d'une communauté affaiblie (faible abondance d'espèces cleptoparasites, sur‑dominance d'espèces de la famille des Halictidae), certaines des localités Parisiennes échantillonnées présentent une diversité d'espèces relativement élevée, qu'il est important de préserver afin de garantir la pérennité des com‑ munautés de pollinisateurs dans le contexte actuel de croissance des milieux urbains. Des pratiques de gestions émergentes au sein des villes comme l'implantation massive d'abeilles domestiques (près de 700 ruches dans Paris intramuros), pourraient néanmoins fragiliser ces communautés

La diversité des abeilles parisiennes

International audienceDespite the forever increasing urbanization, cities often shelter a significant biodiversity. As many other taxa, wild bees may find refuge in urban areas because of relative favorable conditions compared to intensive agricultural environments. In this study, we compiled our joint work to extend the list of Parisian bees. Over 4 years of monitoring (2011, 2014, 2015, 2016), we recorded 87 bee species in intra-muros Paris. In 2016 we added net captures to our sampling procedures with colored pan traps, which provided 11 additional species. The assemblage now represents 8.8 % of the French fauna of Apoïdae. However, this assemblage is mostly dominated by Halictidae and includes only few kleptoparasitic species highlighting an impoverished community.Malgré les perturbations dues à l'urbanisation grandissante, les villes abritent une biodiversité non négligeable. Comme beaucoup d'autres taxons, les abeilles sauvages peuvent être relativement abondantes dans les zones urbaines du fait de certaines conditions favorables par rapport aux milieux agricoles (absence de pesticides, îlot de chaleur urbain, floraison toute l'année). Dans cette étude, nous compilons nos travaux conjoints afin d'enrichir la liste des espèces d'abeilles parisiennes. Au total, le suivi de 4 années (2011 puis 2014, 2015, 2016) a permis de recenser 87 espèces d'abeilles à Paris intra-muros. L'ajout en 2016 de la méthode de capture avec des filets à papillon en plus de la méthode passive avec coupelles colorées a permis de capturer 11 espèces supplémentaires. L'assemblage, qui représente à ce jour 8,8 % de la diversité spécifique des abeilles sauvages de France métropolitaine, est cependant dominé par les Halictidae et ne compte que quelques espèces cleptoparasites, témoignant d'une communauté appauvrie