Loreti, J., M. Oesterheld, and O. E. Sala. 2001. Lack of intraspecific variation in resistance to defoliation in a grass that evolved under light grazing pressure. Plant Ecology. (in press) (Abstract)

------Intraspecific variation in the resistance to grazing has been studied in species from grasslands with long evolutionary history of grazing. Here, we explore the intraspecific variation in grazing tolerance and avoidance of Paspalum dilatatum (Poir.), a grass from the Flooding Pampa (Argentina), where grazing is a novel disturbance. We performed a clipping experiment in a greenhouse with two populations of P. dilatatum from sites with contrasting short term grazing regime: continuous grazing and 20 year-old exclosure. The populations did not differ in their tolerance to clipping. However, the population from the grazed site had slightly higher blade:sheath and root:shoot ratios, and was slightly more affected by clipping in terms of plant height. Both the lack of intraspecific variation in defoliation tolerance and the small variation in grazing avoidance contrast with the notable divergence found between ecotypes of grasses from ecosystems subjected to intense grazing pressures during evolutionary time.