DIET OF THE VIZCACHA LAGOSTOMUS-MAXIMUS (RODENTIA, CHINCHILLIDAE), HABITAT PREFERENCES AND FOOD AVAILABILITY IN NORTHERN PATAGONIA, ARGENTINA

Composition and seasonal changes in the diet of the vizcacha (plains v izcacha) were determined in four habitats of La Payunia Protected Area , through faecal analyses and in relation to food availability. Space use of vizcachas in the spatial heterogeneity (a mosaic of plains and rocky elevations) was evaluated by means of vizcacheras (burrows) loca lization. Diet included 29 genera of plants, mostly grasses and forbs, Poa and Panicum being main dietary elements. Vizcacha did not appear as a generalist herbivore, since grasses constituted 94 % of the diet, and only three grasses were used frequently. A high selectivity ocurr ed in habitats and seasons with low plant diversity. This fact does no t agree with the optimal foraging theory, and may reflect a forced sel ectivity induced by the low quality of available resources for vizcach as in La Payunia. Scarcity of forbs could explain this low nutritional resources quality. Rocky elevations, the habitat of Lagidium viscacia , was not inhabited nor visited for feeding by vizcachas, although 26 % of vizcacheras were found at the foot of these elevations. Dietary p references and antipredation strategy would explain why vizcacha restr icted its habitat to plains.