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Rodent Herbivory influences grassland plant communities.

Cyrwus, Michael*,1, Wallace, Linda1, 1 University of Oklahoma, Norman, OK

ABSTRACT- Herbivory by small mammals is often overlooked or thought of as being insignificant in relation to the role played by larger ungulates. This study focuses on the ecosystem-level effects of small mammals. We are conducting a three-year field experiment to study the effect of cotton rats (Sigmodon hispidus) in a tallgrass prairie. We seasonally measured plant community characteristics, grazing intensity (GI), soil nutrient properties, litter quality, and the spatial activities of three different densities of cotton rats using a series of 0.01 ha field enclosures in a randomized block design. Grass biomass after four months was reduced in the presence of rats (p=0.09). Overall grazing intensities ranged from 19 % with high rodent densities to 15% with intermediate densities. No preferential herbivory has been seen between grasses and forbs (p=0.37). Constrained ordination shows a slight negative response of grasses to herbivory. Soil C:N ratios are highest in those enclosures with no herbivores, possibly due to more C inputs from aboveground and standing litter. Total C and N levels are highest in soils with herbivory. Soil N mineralization rates are currently being prepared and analyzed, and may indicate whether N may be leaving the system, either through leaching or via immobilization. Areas of high rodent activity such as debris piles and latrine areas represent significant pathways that may speed up nutrient cycling in this system.

Key words: grazing, rodent, Oklahoma, grasslands

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