Relative abundance and diet composition of Chacoan cavies in relation to range condition

Abstract

The relative abundance and dietary botanical composition of the Chacoan cavy (Pediolagus salinicola) was studied on sites of very good, good, and poor range condition in the Western Chaco, Argentina. Pellet count data showed that Chacoan cavy densities varied (P<0.001) among these areas. In both seasons, the highest number of pellets was found in the area of poor condition. This area was characterized by an absence of grasses, dense cover of a creeping fern (Selaginella sellowii), thorny shrubs and a scarcity of dicot herbs. In contrast, a decrease (P<0.05) in Chacoan cavy densities was found in the good and very good range condition areas, coincident with the increase of grass and forb cover. Fecal analysis showed that Chacoan cavy diets were greatly influenced by the amount of forage available, which varied according to the condition of the rangeland. Forbs were the main forage class consumed in all range conditions, but the species composition differed among condition classes. For example, several species of dicot forbs were consumed in areas of very good and good range condition, but Selaginella sellowii was the main dietary forb when the range condition was poor. We concluded that range condition affected the relative abundance and diet of Chacoan cavies of Western Chaco, Argentina. High Chacoan cavy density should be considered as an indicator of vegetation depletion caused by other factors rather than a primary cause of savanna degradation.