Jaramillo and Detling raised samples of blue grama (Bouteloua gracilis) from heavily grazed prairie dog (Cynomys ludovicianus) colonies and lightly grazed uncolonized sites in Wind Cave National Park, South Dakota, under controlled conditions to determine the impact of grazing history on several variables: production, nitrogen uptake, and biomass and nitrogen allocation following defoliation. Off-colony plants produced greater biomass (121%) and more nitrogen (203%) that on-colony plants. On-colony plants allocated greater biomass and nitrogen to roots than off-colony plants, which had greater allocation to leaf sheaths and reproductive structures. The authors note that the results support the hypothesis that genetically based morphological and physiological differentiation has occurred in blue grama as a result of strong selection pressures from grazing mammals on prairie dog colonies. They suggest that on-colony population displays a strategy that reduces grazing severity rather than a grazing tolerance response to aboveground herbivory.
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