Response of Macrophyte Traits to Herbivory and Neighboring Species: Integration of the Functional Trait Framework in the Context of Ecological Invasions

With the increase in the number of introduced species each year, biological invasions are considered as one of the most important environmental problems for native biodiversity. In invaded habitats, the establishment of exotic plant species depends on the abiotic and biotic environment. Herbivores and neighboring plants (native or exotic) comprise an important part of the latter. Herbivores cause trophic and non-trophic damage to focal plants, which respond to herbivory by varying their different traits quantitatively (e.g., growth rate and biomass changes) and qualitatively (e.g., variation in morphological and chemical defenses strategies affecting plant palatability). Neighboring plant species also affect functional traits and the fitness of focal plant species, thus herbivore effects on a focal plant could also depend indirectly on the palatability and defensive traits of the neighboring species inside the community. Here, in a first step toward the integration of associational susceptibility/resistance theories in the field of ecological invasion, we performed a microcosm experiment to consider the effects of an exotic crayfish on the growth rate, morphological traits and damage level of three macrophytes (two exotic, one native) growing in pairwise combinations. We found that (i) the response to herbivore presence and to neighboring species identity seemed to be species specific, and (ii) crayfish enhance the fragmentation rate of the two exotic macrophytes Ludwigia grandiflora and Egeria densa in the presence of the native macrophyte Myriophyllum spicatum, which could indirectly facilitate their invasion success. Indeed, fragmentation can increase dispersal abilities of the exotic macrophytes considered in this study as they are able to generate new plants from their fragments. However, our results showed that the interaction herbivore-neighbor species was hardly significant. Our paper presents some first results on associational resistance/susceptibility and lays the foundation for developing a general framework that combines plant community ecology and biological invasion ecology to explain invasive species success

Les plantes envahissantes des corridors fluviaux (traits biologiques, impacts de Ludwigia péploides et L.grandiflora en Loire moyenne et implications pour la gestion.)

Dans le bassin de la Loire, et plus particulièrement en Loire moyenne, deux espèces de Jussies (Ludwigia peploides (Kunth) Raven subsp. montevidensis (Spreng.) Raven, L. grandiflora (Michx.) Greuter & Burdet subsp. hexapetala (Hook. & Arn.) Nesom & Kartesz) amphiphytes exotiques invasives colonisent principalement les annexes hydrauliques et les grèves du lit endigue . Cette thèse étudie la biologie (reproduction, implantation, dissémination, ) de ces deux taxons, leurs impacts sur les communautés végétales et animales (macroinvertébrés aquatiques) afin de mieux adapter leur gestion. Les résultats des suivis de terrain et des expérimentations in situ et ex situ démontrent en particulier: (i) des différences entre les deux espèces concernant leurs traits reproductifs et leur développement sur les annexes hydrauliques et les grèves, (ii) la possibilité d un cycle de reproduction sexuée complet sous le climat ligérien, (iii) un impact nul sur les communautés végétales d hydrophytes mais négatif sur les communautés riveraines étudiées, (iv) peu de différences entre la diversité et la structuration des communautés d invertébrés dans les herbiers de macrophytes autochtones et exotiques. A partir de ces résultats, nous proposons de mettre en oeuvre un protocole de veille et de gestion des Jussies dans les deux types d habitats (annexes hydrauliques et grèves), en intégrant tout particulièrement la nouvelle donnée de forte probabilité de reproduction sexuée.In the Loire catchment, and particularly in the middle Loire River, two species of water primroses (Ludwigia peploides (Kunth) Raven subsp. montevidensis (Spreng.) Raven and L. grandiflora (Michx.) Greuter & Burdet subsp. hexapetala (Hook. & Arn.) Nesom & Kartesz) which are invading exotic amphiphytes. They, mainly colonize former channels and river banks in the in between-dykes floodplain. This thesis studies the biology (reproduction, establishment, dispersal, ) of those two taxa, their effects on plant and animal communities (aquatic macro-invertebrates) in order to optimize their management. The results of the field surveys as well as in situ and ex situ experimentations show in particular: (i) differences between the two species concerning their reproduction features and their development in former channels and river banks, (ii) the possibility of a complete sexual reproduction cycle in the climatic conditions of the middle Loire River, (iii) the absence of effetcs on hydrophyte communities but a negative one on riparian communities, (iv) few differences between the diversity and the structure of invertebrate communities in stands of both native macrophytes and exotic ones. From those results we suggest a survey and management protocol for water primroses in the two types of habitats (former channels and river banks), including in particular the new piece of data on high probability of sexual reproduction.TOURS-Bibl.électronique (372610011) / SudocSudocFranceF

Multitemporal Remote Sensing Based on an FVC Reference Period Using Sentinel-2 for Monitoring Eichhornia crassipes on a Mediterranean River

International audienceInvasive aquatic plants are a serious global ecological and socio-economic problem because they can cause local extinction of native species and alter navigation and fishing. Eichhornia crassipes (water hyacinth) is a dangerous invasive floating plant that is widely distributed throughout the world. In Lebanon, it has spread since 2006 in the Al Kabir River. Remote sensing techniques have been widely developed to detect and monitor dynamics and extents of invasive plants such as water hyacinth over large areas. However, they become challenging to use in narrow areas such as the Al Kabir River and we developed a new image-analysis method to extract water hyacinth areas on the river. The method is based on a time series of a biophysical variable obtained from Sentinel-2 images. After defining a reference period between two growing cycles, we used the fractional vegetation cover (FVC) to estimate the water hyacinth surface area in the river. This method makes it possible to monitor water hyacinth development and estimate the total area it colonizes in the river corridor. This method can help ecologists and other stakeholders to map invasive plants in rivers and improve their control

Late-acting self-incompatible system, preferential allogamy and delayed selfing in the heteromorphic invasive populations of <i>Ludwigia grandiflora subsp. hexapetala</i>

International audienc

Les invasions biologiques dans le Parc naturel régional de Brière : présentation d'une recherche-action

Sur le territoire du parc naturel régional de Brière, les invasions biologiques ne sont pas un phénomène nouveau et les conséquences s’avèrent d’ores et déjà importantes écologiquement, humainement et économiquement. Des réflexions et expérimentations réunissant gestionnaires et scientifiques sont donc conduites localement afin qu’émergent des méthodes de gestion adaptées à la complexité des problèmes posés par les espèces invasives

De nouvelles mauvaises herbes en zones humides : les formes terrestres des Jussies invasives sur prairies

Espèces invasives déjà bien connues car particulièrement problématiques dans les milieux aquatiques, les Jussies (Ludwigia spp.) continuent de surprendre à la fois les gestionnaires et les chercheurs par leurs capacités de colonisation de nouveaux biotopes. Depuis quelques années, elles se développent notamment sur des prairies humides dans des milieux à forte valeur patrimoniale. Les définir pour mieux les comprendre permet d’envisager l’efficacité des mesures et les difficultés rencontrées lors des actions de gestion

Les invasions biologiques dans le Parc naturel régional de Brière : présentation d'une recherche-action Biological invasions in the natural regional Reserve of Brière: applied research for management

Sur le territoire du parc naturel régional de Brière, les invasions biologiques ne sont pas un phénomène nouveau et les conséquences s’avèrent d’ores et déjà importantes écologiquement, humainement et économiquement. Des réflexions et expérimentations réunissant gestionnaires et scientifiques sont donc conduites localement afin qu’émergent des méthodes de gestion adaptées à la complexité des problèmes posés par les espèces invasives.<br>The Marshes of Brivet and Brière, located at the north of the estuary of the River Loire, cover20.500 haregistered in the network of the sites Natura 2000 and mainly localised in the perimeter of the regional natural reserve of Brière (49 000ha). Among the pressures which are exerted there on the conservation of the biodiversity and the uses, biological invasions are not a new phenomenon but in 2 decades, it increased and now is currently regarded as a major problem. For the manager, the success of control and even more the eradication of an immigrant species depends on implementation of human, financial, scientific, technical means largely exceeding the territorial limits… and seldom joined together. However, the specific mono approach is confronted with the multiplication of invasive, animal and vegetable species, which increases the costs whereas the manager is in a context of limited means. The field manager must take into account huge ecosystemic changes, where inter specific exotic-native but also exotic-exotic relations appear; he solicits the scientists then. In collaboration, scientists and managers analyse the situation and test to pass from the complex management of invasive to the management of the complex of the invasive ones

Point de vue – Des macrophytes et des humains : quel avenir possible ?

Considérés tantôt comme des nuisances, tantôt comme des atouts, les macrophytes restent au cœur de nombreux débats. Quelle en est l’histoire récente ? Comment envisager l’avenir avec ces acteurs importants des milieux aquatiques