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

How invasion by Ailanthus altissima transforms soil and litter communities in a temperate forest ecosystem

International audienceThe invasive tree Ailanthus altissima (Mill.) Swingle (tree of heaven) is considered as an ecosystem transformer, which alters plant communities in open areas and forests. Nothing is yet known about its potential effects on forest soil biota and ecosystem functioning. We present here the first study assessesing the impact of A. altissima on soil and litter invertebrate communities in a temperate forest. We analyzed the effect of varying A. altissima densities in a forest of north-eastern France on soil microbial activity, diversity of various litter and soil invertebrate groups (Arthropoda, Lumbricidae, Gastropoda), diversity of functional groups (predatory, detritivorous, coprophagous, phytophagous), and trophic structure. Our study shows that increasing density of A. altissima is associated to lower soil microbial activity, decreasing abundance of litter detritivores (Acari and Collembola) and aboveground predatory Coleoptera, and decreasing species richness of terrestrial Gastropoda. In contrast, increased A. altissima density corresponded with greater abundances of litter Lumbricidae and aboveground coprophagous Coleoptera. We found an overall impact of A. altissima invasion on the soil food web structure that could accelerate the mineralization of organic matter and potentially favor nitrophilous plant species in understory plant communities

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc