Abstract
Populations of grasses exposed to grazing by vertebrates often exhibit reduced stature, increased tillering, reduced flowering, and other morphological differences which distinguish them from ungrazed populations. These differences frequently are interpreted as an adaptive response which reduces grazing damage; however, there are few experimental tests of this hypothesis. This paper describes a field experiment designed to determine whether morphological variation among genotypes of the grass Bouteloua gracilis is related to variation in their responses to grazing. Eleven genotypes differing with respect to morphological and reproductive characters were transplanted into a shortgrass steppe community near Fort Collins, Colorado. Replicates of each genotype were subjected to clipping treatments intended to realistically simulate three grazing intensities. After two growing seasons, different genotypes still maintained significant differences with respect to a wide range of morphological and demographic characters. However, there were few significant effects of grazing treatment, and no significant genotype x treatment interactions. These results suggest that for B. gracilis clipped in simulation of natural grazing, (1) defoliation has few short-term effects on fitness components, and (2) intrapopulation morphological variation has few consequences for defoliation resistance.