Frequent and intense defoliation of grasses has been associated with the evolution of "grazing morphotypes" that exhibit a variety of vegetative traits correlated with improved grazing resistance. While recovery from a seed bank is not considered an important grazing resistance mechanism, relatively little is actually known regarding seed (caryopsis) production in grazing morphotypes of caespitose grasses. The goal of this research was to compare components of seed production in 2 populations

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... sideoats grama (Bouteloua curtipendula var. caespitosa Gould & Kapadia) from nearby sites with different histories of livestock grazing. This was done using vegetative propagules of genotypes from both populations in a greenhouse study. The study was conducted in 2 flowering seasons under conditions considered favorable for seed production. The population exposed to livestock grazing showed a genetically based decrease in seed production relative to the ungrazed population. Lower seed production per plant in the grazed population was at least partially due to reduced numbers of tillers and panicles per plant and spikes per panicle that may be associated with selection for grazing tolerance. The grazed population also exhibited lower average seed production per spike indicating lower inherent floral fertility. Seed production was not closely correlated with vegetative traits associated with increased grazing tolerance, nor was there evidence of obvious physiological trade-offs related to decreased seed production in the grazed population. Lower seed production potential in populations of sideoats grama intensively grazed by livestock may lead to reduced potential for seedling colonization. Key Words: B o u t e l o u a, defoliation tolerance, evolution, grazing resistance Grasses that are exposed to herbivores often possess unique life history, morphological and physiological traits (Carmen and Briske 1985 , Briske and Richards 1995 , Briske 1996 . When defoliation has been frequent over long periods of time, these traits may be associated with the evolution of genetically based defoliation tolerance and the emergence of "grazing morphotypes" in the plant populations affected (e.g., Detling and Painter 1983 , Aarssen and Turkington 1985 , Carmen and Briske 1985 , Painter et al. 1989 , 1993 , Smith 1998 . Defoliation tolerance in caespitose grasses is commonly correlated with a series of vegetative traits including reduced plant height, a less upright growth form, fewer and smaller leaves, and increased tiller number (Briske 1996) . Previous research (Smith 1998) compared vegetative responses under varying defoliation regimes of genotypes from 2 populations of sideoats grama (Bouteloua curtipendula var. caespitosa Gould & Kapadia) with different livestock grazing histories. In