Diet selection of the plains vizcacha (<i>Lagostomus maximus</i>, family Chinchillidae) in relation to resource abundance in semi-arid scrub

Abstract

The diet of the plains vizcacha (Lagostomus maximus) was studied in semi-arid scrub of central Argentina from November 1985 to May 1987 as a basis for understanding the effects of this herbivore on plant communities. Diet composition was documented with microhistological analyses. Fecal nitrogen, an index of diet quality, and vegetation cover were used as measures of resource abundance. Vizcachas consumed a wide variety of grasses, forbs, and shrubs. Grasses were observed in the feces significantly more than expected on the basis of plant cover in the field. Intensive foraging on grasses is consistent with observations of a lower abundance of grasses on colony sites than in the surrounding matrix. Diet quality and breadth of the grass–forb component of the diet were strongly correlated, and comparisons within a season between years showed that diet selectivity decreased with increasing plant cover. Our results contrast with many other studies of foraging strategies that have shown higher selectivity with increasing resources. The inverse relationship we observed could be related to constraints on diet selection due to low food availability.