Vole foraging patterns and plant response in a tallgrass prairie assemblag

Prairie and meadow voles (Microtus ochrogaster and M. pennsylvanicus, respectively) are small herbivores (30-50g), and yet they can dramatically affect composition, diversity, and succession in prairie plant communities. To better understand the mechanisms behind vole effects, vole foraging and plant response to vole herbivory in tallgrass prairie were studied at an experimental tallgrass prairie restoration the Morton Arboretum near Chicago, Illinois. Single-choice feeding trials using vegetative parts revealed that prairie and meadow voles preferred different plant species ( Solidago rigida and Phalaris arundinacea, respectively), but both avoided Penstemon digitalis while the other seven species tested were neither preferred nor avoided. Censuses of clipped and unclipped stems of twelve plant species at the restoration showed that patterns of vole herbivory in the field did not match the results of the feeding trials, with the exception of P. arundinacea, which was the most preferred and most clipped species. Stem size appeared to be an important factor in whether voles clipped stems of plants; stems over seven millimeters were not clipped. Another factor that influenced vole clipping patterns was whether ripe seeds were present at the tips of plant stems.;Plant response to the timing and frequency of vole herbivory on plant vigor and reproductive output was studied by limiting vole access to individuals of three plant species (Desmanthus illinoensis, Echinaea purpurea , and Heliopsis helianthoides) during different portions of the growing season. The effects of timing depended on the plant species; D. illinoensis was negatively affected by early growing season herbivory, E. purpurea was affected by late growing season herbivory, and H. helianthoides was unaffected by herbivory in any one portion of the growing season. Repeated herbivory reduced plant vigor and reproductive output. The effects of vole herbivory timing and frequency carried over from the growing season in which the herbivory occurred into the subsequent growing season when the plants were protected from herbivory for D. illinoensis but not for E. purpurea. Vole clipping patterns and differences between plant species in the effects of clipping and in the carryover of those effects are likely important factors driving vole-mediated plant community change.