Pricklypoppies are listed as a weed in some areas. Cattle, and probably bison before them, avoid eating these sharp leaved plants. Cattle, in more restricted grazing areas, can have a more concentrated effect. Kind of like humans. These plants increase in grazed areas. It's also intersting to note that these plants have spread east along the I-80 corridor as far as Indiana. Two examples of habitat change having the opposite effect of what we usually worry about.