Predator identification methods in diet studies: uncertain assignment produces biased results?

Diet analyses are critical for understanding the ecology of animal species and designing management and conservation strategies. Nonetheless, diet studies of many mammalian carnivores are based on indirect analyses (mostly through their faeces) rather than on direct observations of their feeding behavior, introducing varying degrees of uncertainty into predator species identification. Here, we tested the hypothesis that trophic similarity between diet studies are associated with the predator identification method used by comparing results obtained in studies that used either high confidence identification (HCI; i.e. genetic or chemical analyses of faeces, or stomach or colon content) or low confidence identification methods (LCI; i.e. faeces appearance) for jaguars and cougars. We reviewed the literature on diet of these species and 1) assessed if similarity of the diet was related to the method used to identify the species, and 2) assessed the possible consequences that potential misidentification of faeces could have on diet descriptions (i.e. prey potentially included or omitted). For both aims we took into account the influence of geographical distance between study sites. Furthermore, we briefly summarized the most reliable knowledge currently available about the diets of both species. Our analyses indicated that the method used for predator identification significantly influences diet similarity, with HCI studies being more similar among them than LCI studies or HCI-LCI studies. Studies based on LCI methods apparently overemphasized the importance of reptiles, rodents, and some mesocarnivores in the diet of both predators, whereas other prey items were not detected. Although approaches for a reliable identification of predators are expensive and require specialized technicians and equipment, we highlight the need to invest in them in order to accomplish a better ecological understanding of the feeding ecology of carnivore species, which is a key factor to consider in conservation and management plans.