02158naa a2200265 a 450000100080000000500110000800800410001910000190006024501140007926000090019352014280020265000160163065000110164665000160165765300140167365300220168765300140170965300140172365300180173765300220175570000180177770000190179570000190181477300590183317918482017-04-05       1992    bl ---       0--  u    #d1 aHOLLAND, E. A.  aPhysiological responses of plant populations to herbivory and their consequences for ecosystem nutrient flow.  c1992  aWe explored how responses of two populations variable in grazing tolerance provide feedbacks to nutrient supply by controlling carbon supply to soil heterotrophs. The study focused on differences in production and carbon and nitrogen allocation patterns between the two population. The grazing-tolerant population, or non-colony population, is found on intensively grazed prairie dog colonies, and a grazing-intolerant population, the off-colony population, is found in uncolonized grasslands. Equations describing the production and allocation responses to defoliation for the two ecotypes described were incorporated into CENTURY, a nutrient cycling simulation model. Simulations showed an increase in plant production that paralleled increases in net nitrogen mineralization. Production was greather with grazing and was maintened at higher grazing intensities for the on-colony than the off-colony population. Differences between the populations provide important controls over nitrogen losses. Feedback between plant responses to grazing and nitrogen cycling accounted for increased nitrogen availability with grazing. These feedbacks were more important determinants of ecosystem function than were fertilization effects of urine and feces deposition. The simulation results suggest that ecosystem function may be sensitive to physiological differences in population responses to periodic disturbances like herbivory.  aEcossistema  aPlanta  aPopulação  aEcosystem  aFluxo de nutrient  aHerbivoro  aHerbivory  aNutrient flow  aPlant populations1 aPARTON, W. J.1 aDETLING, J. K.1 aCOPPOCK, D. L.  tAmerican Naturalistgv.140, n.4, p.685-706, Oct. 1992.