Influence de la qualité de l’habitat sur la population adulte du Nacré de la Bistorte

Details

Supervisors

Schtickzelle, Nicolas ; Brans, Victor

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

enIn the context of the biodiversity crisis characterized by a drastic decrease in species diversity and abundance, habitat loss is a major threat. Functional habitat is the environment in which an organism lives, feeds, reproduces and performs other vital functions. Boloria eunomia, or the bog fritillary, is a butterfly that is a double specialist of bistort (Bistorta officinalis), which is both its host plant for larvae and its main source of nectar as an adult. This species is interesting to study given its dependence on specific habitats. The objective of this work is to analyze how habitat quality affects the abundance of adult populations of Boloria eunomia in the Belgian Ardennes. The density of Boloria eunomia was analyzed according to explanatory variables such as bistort cover, the number of tussocks, Ellenberg indicators (nitrogen, light, humidity, pH, temperature) and site openness. The results of the Capture-Mark-Recapture method reveal a significant decline in populations between 2023 and 2024. Then, two models are built: a 2024 model and a multi-year model that groups datas of years 2019, 2023, and 2024. In 2024, bistort cover and the Ellenberg N index are the most significative variables. The multi-year model (2019, 2023, 2024) confirms the central role of bistort but attributes a more moderate weight to nitrogen. Nevertheless, studies on the subject suggest rather average or moderately high levels of nitrogen are beneficial for the host plant. The differences between the two models are probably explained by the temporal coverage and limited data of the 2024 model, leading to greater uncertainty in its estimates. Variables such as humidity, light, pH, and temperature seem to have a negligible effect, probably due to similar conditions between sites. The role of tussock moths remains limited, although biases related to the lack of analysis of their physical characteristics are possible. The opening of the site, only assessed in 2024, seems to be a relevant variable to continue to be integrated in the future. In fact, results show that Boloria eunomia appreciates rather semi-open environments. Ultimately, the multi-year model, is considered more robust thanks to its extended temporal coverage. It takes better account of interannual variations, unlike the year 2024 which is marked by exceptionally high precipitation. Paradoxically, the variance analysis reveals that despite an increase in bistort cover between 2023 and 2024, the density of butterflies has fallen sharply, suggesting the influence of factors not considered, such as the weather. In addition, the Pisserotte site, with low bistort cover, displays the highest densities of the species studied, probably due to its large size and continuity. In order to improve future models, an approach integrating remote sensing tools is proposed as well as a hybrid analysis combining the temporal punctuality of sensors with the spatial analysis of Ellenberg indices. The integration of variables such as climatic and meteorological factors, analysis of the fragmentation, or the presence of parasites could also refine the analysis of the results. This study provides key data on Boloria eunomia in the Belgian Ardennes and contributes to the understanding of the variables influencing its population.