Grazing-mediated differentiation in Agropyron smithii: evidence from populations with different grazing histories

摘要: Agropyron smithii Rydb. (western wheatgrass) was collected from a heavily grazed area colonized by black-tailed prairie dogs (Cynomys ludovicianus) and an adjacent lightly grazed, noncolonized site (ON- OFF-colony populations, respectively). Plants of the two populations were grown in monocultures defoliated nondefoliated interpopulation mixtures at five rates nitrogen (N) addition. We predicted that biomass yield ON- relative to plants would be increased defoliation elevated soil-N availability, potentially selective factors encountered on dog colonies. Biomass distribution among components not significantly altered N-addition treatments, indicating N saturated all N-additions employed. Total did differ significantly, but growth rate greater than across treatments. Defoliation produced similar reduction cumulative populations. Proportional loss individuals, which had fewer larger tillers investment aboveground under defoliation, ON-colony plants. suggest rapid production small contributes prevalence forms A. intensive grazing.