Trophic interactions between the native guanaco (Lama guanicoe) and the exotic donkey (Equus asinus) in the hyper-arid Monte desert (Ischigualasto Park, Argentina)

Exotic herbivores have detrimental effects on the ecosystems where they are introduced, at the level of plant communities and ecosystem processes. The native guanaco Lama guanicoe and the exotic feral donkey Equus asinus coexist in Ischigualasto Provincial Park. We quantified food availability in a plant community in the park during the wet and dry seasons, analyzed diet composition of both herbivores (by microhistological analysis of feces), and assessed the relationship between diet and plant availability and the overlap between donkey and guanaco diets. In both seasons, shrub species represented the most abundant cover type in the area, whereas grasses were the lowest plant cover during the wet season and almost non-existent in the dry season. The diet of the exotic donkey showed a high intake of grasses, and the trophic niche breadth did not change along the year. The guanaco's diet was based on the most abundant food resources (shrubs), which constituted at least 60% of the diet; it was less diverse during the dry season. The diets of donkey and guanaco showed high overlap during the dry season. We can assume, at least during the dry season, the existence of a potential competition between guanaco and donkey, which may be higher if the donkey density increases.