Sample numbers for microhistological estimation of fecal vizcacha diets

Abstract

Precise estimates of diet composition are useful to assess herbivores impact on rangelands and to make management decisions. Since the variability within- and between-samples affect precision of estimates on diet studies, we studied this variability in diets of the rodent vizcacha (Lagostomus maximus Blainv.). We analyzed fecal pellets using a microhistological technique and we estimated the number of samples and subsamples required to achieve given confidence levels. Diets of this herbivore, which is thought to compete with cattle for forage, were studied in November 1994, May, July, and October 1995 in a mixed shrub-grassland community of the southern caldénal in central Argentina. Most grasses, the main components of the diets (> 80%), were estimated with high precision (confidence interval: CI = 10%, p = 0.05) by observing 14 samples and 5 slides per sample. Forbs (5-6%) and shrubs (12%) were estimated with this same number of samples and slides, but yielded a lower level of precision (CI = 20%, p = 0.10). Although our results may not be directly applicable to other vegetation or herbivores, the procedures may be used in other situations to improve precision of diet estimates through microhistological analysis of feces.