The European pond turtle (Emys orbicularis) is a selective generalist with seasonal and geographic dietary flexibility across Europe
Year: 2026
Type: preprint
Abstract: Dietary flexibility allows consumers to cope with fluctuating resources and can stabilise food webs under environmental change, yet its mechanisms remain difficult to quantify in natural systems. We combined multi-marker faecal DNA metabarcoding with seasonally resolved water environmental DNA (eDNA) to link diet composition to local resource occurrence in the European pond turtle ( Emys orbicularis), a generalist omnivore inhabiting dynamic wetlands. We sampled free-ranging populations at a temperate (France-Germany) and a boreal (Latvia) site and assessed spatial and seasonal variation in diet composition, diet breadth, trophic selectivity, and diet-environment overlap within an optimal-foraging framework. Across sites, turtle diets were plant dominated but included diverse animal prey. Diet breadth was higher at the boreal site despite a shorter activity season, supporting the resource-constraint hypothesis. At the temperate site, diet composition shifted significantly across seasons while per-sample diet breadth remained stable. Diet-environment overlap was moderate (Schoener’s D ≈ 0.46-0.57) across sites and seasons, indicating partial resource tracking without mirroring availability. Electivity analyses revealed selective use of specific species, particularly animal prey at the temperate site and certain macrophytes at the boreal site. Together, these results show that E. orbicularis exhibits flexible yet selective foraging, combining partial resource tracking with trophic selectivity rather than passively reflecting environmental availability. By explicitly linking diets to resource baselines sampled at the same time, our study provides a framework to quantify dietary flexibility in situ. This approach helps predict responses of trophic interactions and ecosystem functioning to environmental change and supports evidence-based management of dynamic wetland habitats.
Institution: University of Kassel
Language: English
Subfield: Nature and Landscape Conservation
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
Funders: European Bioinformatics Institute, Joint Programming Initiative Water challenges for a changing world, Biodiversa+, Deutsche Forschungsgemeinschaft, Agence Nationale de la Recherche, National Science Council, Bundesministerium für Bildung und Forschung, Centre National de la Recherche Scientifique, State Education Development Agency Republic of Latvia
Awards: G1281928558, G2359572704, A socio-ecological evaluation of wetlands restoration and reintroduction programs in favor of the emblematic European pond turtle and associated biodiversity: a pan-European approach, G2560476216, G2754497005, G3568042881, G4043177806, G4316240261, G5633068207, G5804512648, G6744965099, G6864176476, G6910909586, G7078626353, G717175753, G8992266079
OpenAlex ID: W7213312031