CONICET | Buscador de Institutos y Recursos Humanos

Abstract The southern vizcacha (Lagidium viscacia) is arock specialist that inhabits small colonies in isolated rockyoutcrops of northwestern Patagonia. This study analyzes itsdiet selection in relation to food availability, establishes thedegree of dietary specialization, and discusses the potentialcompetition with exotic herbivores. Diet composition andfood availability were determined in summer and winter ineight rocky outcrops by microhistological analysis of fecalpellets, and food availability was estimated by the BraunBlanquet cover abundance scale. Vegetation cover differenceswere detected by using a random analysis of variance(ANOVA) factorial block design, and dietary preferenceswere determined by the confidence interval of Bonferroni.The southern vizcacha showed a specialized feeding behaviordespite the consumption of a wide variety of items. Theirdiet was concentrated on a few types of food, mainlygrasses, and the trophic niche was narrow and withoutseasonal variations. In winter, when food was scarce andof lower quality than summer, diet was dominated by Stipaspeciosa, suggesting a selection according to the selectivequality hypothesis. Our results (narrow trophic niche,restricted activity near rocky outcrops, and a diet with highproportions of low-quality grasses) showed that the vizcachais an obligatory dietary specialist, and these characteristicsmade it highly vulnerable to changes in foodavailability. In this scenario, overgrazing caused by alienspecies with similar diets, as the European hare and livestock,could negatively affect their colonies.