Painter et al examined four co-occurring perennial grass species: Bouteloua gracilis, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii from eight locales in South Dakota. Active-colony plants were more frequently and more heavily grazed than those at other grazed locales. In situ, plants from heavily grazed populations were smaller and more prostrate than those from populations with little to no grazing (including the extinct colony) and interpopulation variation corresponded to current grazer use. After several growing seasons in common environments, there were still significant interpopulation differences; however, variation often corresponded with grazing history. Although differences between active-colony and noncolony plants were somewhat reduced, active-colony plants were still smaller and more prostrate. However, extinct-colony plants more closely resembled active-colony plants than noncolony plants. Morphological variation among these populations is the result of more than simple grazer use historical factors and the dynamic nature of the grazing regimes are also contributing factors.
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