Abstract

The mountain viscacha (Lagidium viscacia) and the Andean chinchilla rat (Abrocoma cinerea) are syntopic species in the Andean highlands of northern Chile. Given that in this environment food availability is scarce, we predict that these rodents would select different food items in order to avoid presumable competition for food. We described the food habits of mountain viscachas and chinchilla rats in the highlands of northern Chile during contrasting seasons: winter (1996) and summer (1997). Results indicate that: (1) Out of the 12 plant species available. L. viscacia consumes 10 species during the winter and seven during the summer. The main species eaten was Stipa bomanii, making 20.9 and 30.1 % of the winter and summer diets, respectively. Other important plants consumed only during the winter were Nicotiana longibracteata (12.1 %) and Parastrephia quadrangularis (9.4 %). In turn, Festuca ortophylla (19.9%) was eaten only during the summer. The main plants consumed by A. cinerea during the winter were Baccharis tola (73.2 %) and Lupinus oreophilus (11.9 %), whereas during the summer these were B. tola (33.7 %), Adesmia horrida (22.5 %), and L. oreophilus (24.0 %); (2) L. viscacia had a broader trophic niche than A. cinerea (winter H' = 0.67 versus 0.25: summer H' = 0.53 versus 0.56, respectively). (3) During winter, L. viscacia showed high selection for N. longibracteata (Ei = 0.96) and Calceolaria stellarifolia (Ei = 0.80), and lower for P. quadrangularis (Ei = 0.62) and S. bomanii (Ei = 0.26), whereas during summer it selected the graminoids F. orthophylla (Ei = 0.52) and S. bomanii (Ei = 0.42). In contrast, A. cinema selected L. oreophilus (Ei = 0.91) and B. tola (Ei = 0.35) during the winter and L. oreophilus (Ei = 0.92), A. horrida (E = 0.56) and E. rupestris (E = 0.55) during the summer. During summer season P. quadrangularis was rejected (Ei = -0.40) by A. cinerea. (4) Both rodents showed low food overlap during both seasons (CH = 0.18 and 0.06 for winter and summer, respectively). In sum, these herbivorous species live in the same place and have rather broad diet selection, especially L. viscacia, which is more generalist than A. cinerea. However, they have distinctive trophic niches so that, unless during the sampled seasons, competition for food is unlikely.