Cécile VANPE, Tanguy DAUFRESNE, Mélanie ROY, Jérôme SENTILLES, Pierre-Yves QUENETTE, Christophe BALTZINGER

Species will be required to disperse rapidly through fragmented landscapes in order to keep pace with the changing climate. In this context, long-distance dispersal of diaspores is recognized as a key mechanism in plant dynamics and helps plants track their niches and migrate in altitude. Omnivorous Ursids are likely to be good vectors of long-distance dispersal of plants due to their large body size, predominantly plant-based diet, high mobility, large home ranges, large diversity of habitats and long gut retention time.
We investigated the endozoochorous dispersal of plant diaspores by the brown bear (Ursus arctos) in the critically endangered Pyrenean population situated in south-western Europe. To get a comprehensive view of the full process and the different filters that affect the dispersal effectiveness, we combined faecal DNA metabarcoding, coproscopic analyses, germination experiments under greenhouse and an in natura experiment.
We identified 53 different plant taxa in the diet. Among the 16 species for which we could find information on the fruiting period, three fleshy-fruited and six dry-fruited plants were consumed during their fruiting periods. Intact diaspores extracted from faeces samples belonged to 27 different taxa, including 15 herbaceous plants, six fleshy-fruits and one diaspore dry fruit. We described the dispersal of plants that produce dry or fleshy fruits, as well as ferns and mosses. We also highlighted the importance of considering the endozoochory process up to the faecal matrix, which can limit germination. We finally showed that dung beetles play a unique role in the disintegration of faeces and the secondary dispersal of diaspores.
Overall, this study revealed the dispersal of a wider range of plants than previously thought in Ursids, which could influence the structure and dynamics of Pyrenean plant communities and consequently the functioning and resilience of Pyrenean ecosystems in the face of global changes.