MORPHOLOGIC AND ALLOZYMIC VARIATION BETWEEN LONG-TERM GRAZED AND NON-GRAZED POPULATIONS OF THE BUNCHGRASS SCHIZACHYRIUM-SCOPARIUM VAR FREQUENS

Plant populations of S. s. var. frequens with a history of long-term grazing by domestic herbivores were characterized by shorter and narrower leaf blades and tillers of lower weight than plants from populations with a history of no grazing. Following 4 biweekly defoliation events plants from the grazed population additionally displayed lower specific leaf weights, lower amounts of biomass removed per tiller upon defoliation and a greater number of new and regrowing tillers. Production values per plant remained similar between the 2 populations because of a greater number of tillers per plant in the grazed population. A large amount of allozymic polymorphism was observed in both the grazed and non-grazed populations. Results of the electrophoretic analyses indicated that a minimum of 66% of the plants sampled represented separate genotypes. No distinction could be made between grazed and non-grazed populations in terms of allozymic partitioning. The morphological variation observed between these 2 populations may represent a shift in the relative dominance of series of genotypes variously adapted to herbivory.