Anne Bonis

Understanding the long-term trends of biological invasions and their drivers is a pivotal issue. However, it is challenging because collecting presence/abundance data of invasive species as well as environmental/biotic factors over a period of years is time-consuming and therefore such data is scarce compared to short-term studies. Here, we investigated whether environmental and biotic factors in highly regulated eutrophic marshlands (water regime, physico-chemistry, habitat features, and predatory fish biomass) successfully accounted for spatiotemporal trends in abundance of small and large red swamp crayfish (Procambarus clarkii) in drainage ditches over seven consecutive years. For this, we used length-frequency data collected during the annual peak in crayfish activity. We also explored whether variation in crayfish abundance over time was due to density-dependent effects (temporal autocorrelation). We found large variation in crayfish abundance expressed in capture per unit effort (CPUE) between ditches and for different years (by a factor of 10 and 6 for small and large individuals) but with no specific trend over time. No density-dependent effect was found in any of the ditches. While crayfish CPUE was poorly related to the water regime (in particular dryness intensity of ditches for small crayfish), it was favoured by densely vegetated banks and negatively linked to the density of surrounding ditches for the two life stages. No relationship was detected with predatory fish biomass or any of the other environmental factors studied. Controlling crayfish abundance by managing environmental conditions seems possible in some cases, but likely costly for other components of biodiversity. Trapping could be a possible strategy when populations dropped to low densities in places. Finally, further studies are needed in ecosystems covering a wider range of environmental conditions to provide a more comprehensive understanding of the long-term trend of the species.

Dynamic Adaptive Policy Pathway (DAPP) maps are used to plan management decisions in contexts of high uncertainty, such as those driven by environmental changes affecting critical assets. Recent discussions emphasize their relevance for addressing complex common-pool resource challenges, where diverse species, actors, and ecosystem services are intricately connected. However, designing DAPPs for such multifaceted social-ecological systems (SES) is challenging due to the extensive range of potential adaptation options.This study presents a general method to address these challenges by leveraging Ostrom’s theoretical frameworks for the governance of common pool resources – the Institutional Analysis & Development framework (IADF), the Social-Ecological Systems framework (SESF), and the Coupled Infrastructure Systems framework (CISF). These frameworks were used to design nested DAPP maps that structure a large number of adaptation actions across multiple levels of institutional arrangement (operational, collective-choice, constitutional), and then develop a mathematical model to analyze the dynamic robustness of a SES across all potential pathways.The method was applied to predict and understand DAPP maps for supporting the collective management of hedgerow networks delivering diverse ecosystem services. DAPP maps for two SES were compared – one rural and one peri-urban – in France’s agro-ecological landscapes of the Auvergne region. We further modeled the impact of climate change on hedgerows characterized by different size and species richness, revealing the sensitivity of these DAPP maps to transit between nine nested institutional arrangements.We discuss the methodological and practical implications of this approach for managing SES characterized by greater diversities of interconnected species, actors, and ecosystem services, highlighting its strengths and challenges in guiding adaptation under deep uncertainty.

Les effets du régime hydrique (RH) sur la composition spécifique de la végétation de prairies inondables et son caractère plus ou moins hygrophile ont été étudiés in situ pendant quatre années successives dans le Marais poitevin, dans des prairies pâturées extensivement par des bovins. Les résultats obtenus montrent que les trois dimensions du RH mesurées à l’emplacement des relevés floristiques (durée d’inondation, anoxie et sécheresse) déterminent de façon complémentaire la composition des communautés végétales, et leur caractère plus ou moins hygrophile. Les sources de variations de ces dimensions du régime hydrique s’avèrent multiples (niveau du canal, altitude du site et contrastes intra-et intersites, effet de l’année climatique, etc.), et leur importance respective varie selon la dimension du régime hydrique considéré et le secteur du Marais poitevin. Cela suggère que le niveau d’eau des canaux adjacents aux prairies n’est pas un facteur de contrôle essentiel du régime hydrique des prairies inondables actuellement et, en conséquence, des composants des communautés végétales qui y répondent. Les résultats montrent également que les communautés végétales ne sont pas entièrement expliquées par les conditions environnementales observées in situ (régime hydrique et salinité du sol dans le marais argileux). Dans les prairies du secteur tourbeux du Marais poitevin, des données de niveau d’eau des canaux sont disponibles sur près d’un siècle : elles montrent qu’antérieurement aux années 1970, les canaux de certains secteurs présentaient des niveaux d’eau hivernaux nettement plus élevés qu’actuellement et des étiages moins sévères. Ces données partielles suggèrent qu’avant les années 1970, les prairies étaient plus longuement inondées et soumises à des stress hydriques moins forts qu’actuellement. Une hypothèse est que les contrastes de communautés végétales observées dans ce travail, mais non expliqués par les conditions actuelles, reflètent le régime hydrique antérieur de plusieurs décennies, probablement plus humide.

One of the major current ecological challenges is to understand how to reconcile human activities with biodiversity conservation concerns. This issue is particularly relevant in freshwater ecosystems where biodiversity is globally under severe threat. Artificial waterbodies, such as ditch networks, are part of the few remaining wetlands in agricultural landscapes and hence play a crucial role in maintaining aquatic biodiversity in these landscapes. We investigated the responses of adult Odonata assemblages at different spatial scales in a marshland crossed by ditches to two factors expected to be pivotal influences on assemblages. At the local scale, this was mainly the water regime in ditches and, at a broader scale, the composition of the landscape. Both taxonomic alpha and beta diversity, and functional trait composition were considered as response variables. Significant differences were found between the responses of the two Odonata suborders. We showed that Zygoptera species richness decreased and species turnover increased with the duration of drying episodes in ditches. Geographical distances between local assemblages as well as landscape characteristics, notably woodland cover, meadow cover and ditch network length, also significantly shaped the distribution of Zygoptera. For Anisoptera, species richness was not explained by environmental variables and beta diversity was associated only with local conditions; it increased with increasing dissimilarity in water quality and riparian vegetation. We also found evidence of functional trait syndromes (combinations of correlated traits) in Odonata assemblages, but without clear relationships to environmental gradients. This study reveals the structuring role of water regime for Odonata in ditch networks and demonstrates the need to jointly consider environmental variables at different spatial scales to properly understand the distribution of Odonata. Our findings have important conservation implications as the water regime is heavily managed in such ecosystems. Even though the relationship between functional composition and environmental gradients was found to be of limited extent in this study, we discuss how it might provide new insights for Odonata assemblage structure and be useful, locally, for stakeholders and managers. Lastly, we call for further multiscale investigations considering both the taxonomic and functional responses of Odonata assemblages (functional analyses with multiple traits and several species being scarce in this taxonomic group) in other anthropogenic freshwater ecosystems to gather more lessons for their conservation.

Marshlands and floodplains are generally characterized by a long history of human occupation and management, with strong impacts on biodiversity. In these landscapes, ditch networks often represent the last or most significant aquatic habitat, and significantly contribute to regional biodiversity. To determine the drivers of biodiversity in ditch networks, especially the importance of the water regime, we monitored vegetation in ditches in 11 sites (independent blocks of ditch networks) of an Atlantic marshland (the Marais poitevin, France) over a 4-year period, and a panel of local environmental conditions and landscape characteristics. Large differences in the species richness and composition of ditch plant communities were observed among sites. The water regime had a predominant effect on all descriptors of ditch plant communities. High water levels combined with strong temporal variability, including drying-out periods, were found associated to the communities with the highest species richness. By contrast, water quality parameters did not influence plant communities across sites. Among landscape variables, woodland cover combined with high hedge cover along the ditches significantly influenced plant composition and species richness. These results are discussed in terms of management actions that may promote the diversity and composition of ditch plant communities and address conservation challenges.