In an experiment at Texas A & M, Briske et al. found the tallgrass, A. geradii, exhibited inflexible allocation priorities, while the shortgrass, B. rigidiseta, exhibited flexible allocation priorities in response to defoliation, which corresponded with their initial designations as herbivory-sensitive and herbivory tolerant species, respectively. The concentration of 13C within new leaves of S. scoparium increased in response to a single defoliation, while the percentage and concentration of 13C within roots was reduced. Selective herbivory may contribute to S. scoparium's designation as an herbivory-sensitive species, even though it possesses flexible allocation priorities in response to defoliation. Alternatively, the recognized herbivory resistance of A. purpurea may be a consequence of infrequent and/or lenient herbivory associated with the expression of avoidance mechanisms.
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