Trophic preferences in an assemblage of mammal herbivores from Andean Puna (Northern Chile)

The patterns of plant consumption and preference were assessed for three mammal herbivores, the rodents Abrocoma cinerea and Chinchilla brevicaudata, and the camelid Vicugna vicugna, co-occurring in the Andean Puna (Chile). The plant proportion in the diet estimated from faeces epidermic materials was compared to transect plant cover. Although the harsh climatic conditions constrained plant availability (low vegetation, xerophytic species rich in secondary metabolites and structural carbohydrates) none of the mammals consumed plants according to their availability, displaying adaptations for efficient plant processing. V. vicugna, with a broad trophic niche, consumed short grasses and secondarily shrubs; C. brevicaudata also combined herbaceous plants and shrubs; and A. cinerea was specialised in shrub-eating. Although trophic overlap between the first two species was moderate, interactions were minimised by the mobility and low-impact grazing of V. vicugna. It is suggested that the diet of the three species differed due to their dissimilar abilities for responding to concentrations of secondary metabolites. The plants preferred by C. brevicaudata and V. vicugna did not carry high nutritional content but rather low content of secondary compounds. Conversely, A. cinerea was able to excrete terpenes, with metabolic costs compensated by the high energetic content of the plants eaten.