Biogeographic comparisons of herbivore attack, growth and impact of Japanese knotweed between Japan and France

International audienceTo shed light on the process of how exotic species become invasive, it is necessary to study them both in their native and non-native ranges. Our intent was to measure differences in herbivory, plant growth and the impact on other species in Fallopia japonica in its native and non-native ranges. We performed a cross-range full descriptive, field study in Japan (native range) and France (non-native range). We assessed DNA ploidy levels, the presence of phytophagous enemies, the amount of leaf damage, several growth parameters and the co-occurrence of Fallopia japonica with other plant species of herbaceous communities.Invasive Fallopia japonica plants were all octoploid, a ploidy level we did not encounter in the native range, where plants were all tetraploid. Octoploids in France harboured far less phytophagous enemies, suffered much lower levels of herbivory, grew larger and had a much stronger impact on plant communities than tetraploid conspecifics in the native range in Japan. Our data confirm that Fallopia japonica performs better-plant vigour and dominance in the her-baceous community-in its non-native than its native range. Because we could not find octoploids in the native range, we cannot separate the effects of differences in ploidy from other biogeographic factors. To go further, common garden experiments would now be needed to disentangle the proper role of each factor, taking into account the ploidy levels of plants in their native and non-native ranges. Synthesis. As the process by which invasive plants successfully invade ecosystems in their non-native range is probably multifactorial in most cases, examining several components-plant growth, herbivory load, impact on recipient systems-of plant invasions through biogeographic comparisons is important. Our study contributes towards filling this gap in the research, and it is hoped that this method will spread in invasion ecology, making such an approach more common

Etude de l'Ailante (Ailanthus altissima (Mill.) Swingle) comme exemple de plante invasive (risques pour la biodiversité de la forêt de Fontainebleau)

L objectif de cette thèse est d étudier l Ailante comme exemple d espèce exotique envahissante et d évaluer les risques que représente sa présence pour la biodiversité en milieu forestier. Ce travail visait à répondre aux quatre questions suivantes : Où trouve-t-on l Ailante dans la forêt, son expansion est-elle significative et comment s opère-t-elle. Quel est son impact sur différents compartiments de la biodiversité ? Quels sont les mécanismes qui permettent son expansion ? Est-il difficile de contrôler les populations ? La zone d étude est la forêt de Fontainebleau où l Ailante progresse régulièrement menaçant des réserves naturelles. Il apparaît que l Ailante s implante durablement en forêt à la faveur de trouées d origine anthropique ou non dans le couvert forestier. Ensuite, il semble que ses capacités allélopathiques et sa reproduction empêchent la régénération des arbres natifs de la forêt. Son impact sur les différents compartiments de la biodiversité a été évalué, en particulier sur le site d invasion le plus important en terme de surface pour le massif forestier, la plaine de Sorques. Des inventaires floristiques ainsi que des échantillonnages lichénologiques et bryophytiques mais également faunistiques pour la litière, le sol et enfin des analyses d activité microbiennes ont été réalisés le long d un gradient de densité de drageons. Nos inventaires floristiques réalisés sur l ensemble du massif forestier suggèrent que l Ailante est associé à une communauté distincte moins riche en espèces que celles qui sont associées aux autres espèces d arbres à feuilles caduques de la forêt de Fontainebleau. Nos inventaires floristiques sur la plaine de Sorques confirment ces résultats par rapport au Chêne pédonculé. L Ailante est associé à une richesse en Lichens épiphytes moindre que le Chêne pédonculé. L abondance des Acariens et Collemboles de la litière diminuent alors que l abondance des Lumbricidés augmente en fonction de la densité en drageons d Ailante. Globalement les détritivores sont les plus touchés des groupes fonctionnels de la litière par la présence d Ailante. Les Lumbricidés semblent le groupe taxonomique résilient de l écosystème forestier. L abondance des Coléoptères prédateurs diminue et plus particulièrement celle d Abax parallelipipedus qui est l espèce la plus commune dans cette zone ce qui indique une perturbation importante de l écosystème. La richesse et la diversité des Gastéropodes diminuent le long du gradient de densité de drageons. Enfin l activité des microorganismes du sol diminue le long du gradient de densité d Ailante indiquant une perturbation importante de la chaîne de minéralisation des éléments nutritifs. Les conclusions issues de cette étude démontrent que cette espèce invasive des milieux anthropisés et ouverts est également une menace pour l écosystème forestier et que Ailanthus altissima y agit comme une espèce invasive transformatrice en bouleversant les chaînes trophiques au point que ces changements soient observables sur des populations prédatrices de macroinvertébrés. Ces résultats justifient en outre le développement d une méthode de contrôle dite d "infusion" pouvant être intégrée à un protocole d éradication.The objective of this thesis is to study the Tree-of-heaven as an example of alien invasive species and assess the risks that it represents for the biodiversity in a forest ecosystem. The aim of this study was to answer these four questions: Where is located the tree of heaven in the forest? Is its expansion significant? How does it proceed? What is its impact on the different biodiversity compartments? What are the mechanisms that help it to expand? Is it easy to control the populations? The study area is the Fontainebleau forest where ailanthus invade progressively. It seems that Ailanthus establishes durably anthropogenic or not gaps occurring in the tree cover. Afterwards, its allelopathy abilities and its vigorous reproduction prevent the other tree species to recover.The study of the impact on all the compartments of the forest ecosystem was conducted on the largest surface invasion site of the forests. Floristic inventories and lichens and bryophytes sampling but also for the litter fauna, soil and analysis of microbial activity have been made along a gradient of density of suckers. Our floristic inventories conducted throughout the forest suggest that Ailanthus altissima is associated with a distinct community, less rich in species than those associated with other species of deciduous trees of the Fontainebleau forest. Our floristic inventories on the plain of Sorques confirm these results in relation to the common oak. TheTree-of-heaven is associated to less rich community of epiphytic lichens than the common oaks. The abundance of Acari and Collembola in the litter decreases while the abundance of Lumbricids increases with Ailanthus altissima suckers density. Overall detritivores are the most affected functional groups of litter by the presence of Ailanthus altissima. The Lumbricids seem the resilient taxonomic group of the forest ecosystem. The abundance of predatory Coleoptera and especially Abax parallelipipedus (which is the most common species in this area) decreases which indicates a significant disturbance of the ecosystem. The richness and diversity of gastropods decreased along the gradient of density of suckers. Finally the activity of soil microorganisms decreases along the gradient Ailanthus altissima density indicating a significant disturbance in the chain of mineralization of nutrients.The findings from this study demonstrate that this invasive species of open and anthropized habitat is also a threat to the forest ecosystem and that Ailanthus altissima acts as a transforming invasive species affecting dramatically the trophic chains. These results justify further development of a control method known as "infusion" which can be incorporated into an eradication protocolPARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceF

Competition with wind-pollinated plant species alters floral traits of insect-pollinated plant species

Plant traits related to attractiveness to pollinators (e.g. flowers and nectar) can be sensitive to abiotic or biotic conditions. Soil nutrient availability, as well as interactions among insect-pollinated plants species, can induce changes in flower and nectar production. However, further investigations are needed to determine the impact of interactions between insect-pollinated species and abiotically pollinated species on such floral traits, especially floral rewards. We carried out a pot experiment in which three insect-pollinated plant species were grown in binary mixtures with four wind-pollinated plant species, differing in their competitive ability. Along the flowering period, we measured floral traits of the insect-pollinated species involved in attractiveness to pollinators (i.e. floral display size, flower size, daily and total 1) flower production, 2) nectar volume, 3) amount of sucrose allocated to nectar). Final plant biomass was measured to quantify competitive interactions. For two out of three insect-pollinated species, we found that the presence of a wind-pollinated species can negatively impact floral traits involved in attractiveness to pollinators. This effect was stronger with wind-pollinated species that induced stronger competitive interactions. These results stress the importance of studying the whole plant community (and not just the insect-pollinated plant community) when working on plant-pollinator interactions

Short-term climate-induced change in French plant communities

International audienceLatitudinal and altitudinal range shifts in response to climate change have been reported for numerous animal species, especially those with high dispersal capacities. In plants, the impact of climate change on species distribution or community composition has been documented mainly over long periods (decades) and in specific habitats, often torests. Here, We broaden the results of such long-term, focused studies by examining climate-driven changes in plant community composition over a large area (France) encompassing multiple habitat types and over a short period (2009-2017). To this end, eye measured mean community thermal preference, calculated as the community-weighted mean of the Ellenberg temperature indicator value, using data from a standardized participatory monitoring scheme. We report a rapid increase in the mean thermal preference of plant communities at national and regional scales., which we relate to climate change. This reshuffling of plant community composition corresponds to a relative increase in the abundance or warm - versus cold-adapted species. However, support for this trend was weaker when considering only the common species, including common annuals. Our results thus suggest tor the first time that the response of plant communities to climate change involves subtle changes affecting all species rare and common, which can nonetheless be detected over short time periods. Whether such changes are sufficient to cope with the current climate Warming remains to be ascertained

Density‐dependent natural selection mediates harvest‐induced trait changes

International audienceHarvesting has been demonstrated to cause rapid, yield-decreasing trait change towards slower somatic growth and earlier maturation in wild populations. These changes are largely considered to result from direct, density-independent harvest selection on traits. Here, we show that exact same trait changes may also indirectly result from a harvest-induced relaxation of density-dependent (K) natural selection for faster growth and delayed maturation. We exposed 12 pond populations of medaka fish (Oryzias latipes) to contrasted size-selective harvesting during 5 years, and show that harvesting effectively changed juvenile natural mortality from density-dependent to density-independent. We then laboratory-reared medaka progeny under contrasted food levels mimicking the environmental effects of a harvest-induced density gradient. Interaction between past harvest regime and present food environment on progeny traits revealed that harvest-induced trait changes in medaka resulted from selection in a low-food environment only, i.e., were driven by relaxed K-selection only, not by direct harvest selection. Feeding trials further demonstrated that trait changes were associated with reorganizations in rates of food acquisition, assimilation and allocation that were contingent upon the food environments. This is the first study to demonstrate that harvesting can induce undesirable distortions of natural selection that impair productivity traits. We conclude that sustaining harvesting yields over extended time scales requires a preservation of high population densities

Does competition with wind-pollinated species alter Echium plantagineum's attractiveness to a common pollinator Bombus terrestris?

International audienceIn insect-pollinated plants, pollinator attraction is influenced by flowers (e.g. number, size) and their associated rewards (e.g. pollen, nectar). These traits can depend on plant interactions. Indeed, below-ground competition between plants can lead to a decrease in flower or reward production in insect-pollinated species. Wind-pollinated plants, in particular, which are almost never studied in plant pollinator networks, can alter insect-pollinated plants' attractiveness through competition for nutrients. The response of pollinators to such changes has never been investigated.A pot experiment was carried out in which an insect-pollinated species, Echium plantagineum, was grown in binary mixture with three wind-pollinated species selected to exert a panel of competitive interactions. Below-ground competition was controlled using dividers limiting interspecific root competition. Floral traits of E. plantugineum (i.e. flower production, floral display size, flower size and nectar production) were measured. For each species mixture, the visits (i.e. first visit, number of visits, 10-min sequences) of Bombus terrestris individuals released in a flight cage containing two pots were followed, one with and one without below-ground competition.Below-ground competition significantly affected nectar's sucrose concentration but did not influence flower and nectar production. Likewise, pollinator visits were not influenced by below-ground competition. Competitor identity significantly influenced flower and reward production of E. plantagineum, with a decrease in the presence of the most competitive wind-pollinated species. A tendency for faster flower visitation events was also detected in the presence of the least competitive competitor. This study raises new questions regarding the influence of wind-pollinated plants on plant pollinator interactions

Below-ground competition alters attractiveness of an insect-pollinated plant to pollinators

International audienceCompetitive interactions between plants can affect patterns of allocation to reproductive structures through modulation of resource availability. As floral traits involved in plant attractiveness to pollinators can be sensitive to these resources, competition with any neighbouring species may influence the attractiveness of insect-pollinated plants. While pollination research has primarily focused on above-ground interactions, this study aims at investigating if the presence of a competitor plant can modulate neighbouring insect-pollinated plant attractiveness to pollinators and resulting fecundity, especially through below-ground competitive interactions for soil resources. We set up a plot experiment in which we grew an insect-pollinated plant, Sinapis alba (Brassicaceae), in a mixture dominated by a wind-pollinated plant, Holcus lanatus (Poaceae). Individuals of S. alba were either subjected to or isolated from (with buried tubes in the soil) below-ground competition. Across the flowering season, floral traits involved in attractiveness of S. alba and pollinator visitation were followed at the plot and plant level to investigate different scales of attractiveness. At the end of the experiment, seeds were harvested to assess plant fecundity. Competition had a significant negative effect on plot and plant floral display size as well as flower size while nectar traits were not affected. When plants of S. alba were in competition, the time to first visit was altered: the proportion of plots that received a visit was smaller for a given time; in other words, it took more time for a given proportion of plots to be visited and some plots were even never visited. Moreover, pollinators made fewer visits per plots. The proportion of viable seeds produced by S. alba in competition was lower and probably linked to the competition itself rather than changes in pollinator visitation. This study suggests that competitive interactions between plants can modulate pollination interactions even when competing plant species are not insect-pollinated

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