Data for the article: Trophic niche partitioning between two prey and their incidental predators revealed various threats for an endangered species

We captured 44 caribou in the winter of 2013 and 2014 across the Gaspésie caribou range using a net gun fired from a helicopter. We collected caribou hair samples from the rump of the animal, and dried and stored it in paper bags at ambient temperature until processing. We used the same sampling and conservation protocol for hair samples collected from 90 moose, 127 coyote and 57 black bear carcasses across the three Wildlife Reserves that overlap the Gaspésie National Park (Fig. S1). Moose were harvested between September and October 2018 during the sport hunting season whereas coyotes and bears were trapped during the annual predator control program between June 2016 and October 2018 across the Gaspésie caribou range. The capture and manipulation protocols were authorized by the Animal Welfare Committee [Université du Québec à Rimouski (hereafter UQAR) certificate #CPA-52-13-112; Ministère des Forêts, de la Faune et des Parcs (hereafter MFFP) certificate #CPA FAUNE 13-08]. We collected samples opportunistically from all potential food sources consumed by moose, coyotes and bears to describe the composition of their diet. We collected hair samples from 22 individuals belonging to 6 different species that were accidentally trapped during the predator control program, including 4 white-tailed deer (Odocoileus virginianus), 1 snowshoe hare (Lepus americanus), 2 large rodents (groundhog, Marmota monax, North American porcupine, Erethizon dorsatum), 8 Canada lynx (Lynx canadensis) and 7 moose (Alces americanus). We also collected hairs from 22 individuals belonging to 6 species that were harvested by sport trappers or opportunistically collected in the ZEC Casault during summer, including five different species of rodents (1 red squirrel, Tamiasciurus hudsonicus, 2 common voles, Microtus arvalis, 5 deer mice, Peromyscua maniculatus, 6 Northern flying squirrels, Glaucomys sabrinus, and 1 pygmy shrew, Sorex minutus), and one species of large rodent (7 North American beaver, Castor canadensis). We also collected the feathers of 3 ruffed grouses (Bonasa umbellus) and hair from 4 snowshoe hares which were harvested by sport hunters in the ZEC Casault. We dried and stored hair and feathers in paper bags at ambient temperature until processing. Finally, in the study area in 2017, we collected opportunistically six insects from three species belonging to the coleopteran (1 beetle) and hymenoptera orders (3 ants and 2 wasps). We also collected plant samples in July 2017 belonging to 46 different species in the montane boreal forest area of Mount Albert (n = 93) and Mount Logan (n = 72) in the Gaspésie National Park and of Petit Mount Ste-Anne (n = 53) in the Chic-Chocs Wildlife Reserves (see details in Appendix S1). Plant sampling was authorized by the Société des Établissements de Plein Air du Québec, which manages the Gaspésie National Park and the Chic-Chocs and Matane Wildlife Reserves [certificate # PNG-2017042703]. We randomly collected three replicates per species and froze them at -20°C until they were processed. We freeze-dried insect and plant samples for 48h, ground them into a fine powder using a CryoMill (Jardine et al., 2003), and stored them in a desiccator until the stable isotope analysis.