eDNA and metabarcoding for rewilding projects monitoring, a dietary approach

There is an increased interest in the possibility to use large animals in the restoration of degraded ecosystems and to increase the capacity of natural areas to sustain richer biodiversity. We quantify the dietary differences and similarities between five moose and 22 red deer introduced in a 2100 ha fenced area under restoration (Lille Vildmose, Denmark) and their potential in the restoration process. Moose and red deer were selected based on their biogeographic affinity and existing knowledge of their diet and feeding behaviour, and are expected to counteract encroachment on open habitats. Using eDNA metabarcoding of dung collected in the field and species identification through saliva recovered from browsed twigs, we investigated the species' diets and diet overlap after the moose were released into the area, and assessed how their diets match the expected ecosystem function. Despite the partial overlap of some dietary items, such as Betulaceae and Salicaceae, we report a differential use in height of tree species and distinctive use of other food resources between the two species, with red deer eating more herbaceous plants and the moose diet also containing aquatic plants. This study exemplifies a monitoring approach to restoration projects where large herbivores are expected to provide a key ecosystem function through their browsing and grazing.