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Grazing ecosystems support more herbivore biomass than any other terrestrial home ground (Sinclair 1975, Detling 1988, McNaughton et al. 1989, 1991, Huntly 1991). A functional consequence of this disparity in trophic organise emerges by comparing the relationship between surface drudgery and herbivore spending in the Serengeti and Yellowstone ecosystems with that in other terrestrial ecosystems ILLUSTRATION FOR FIGURE 3 OMITTED. For custom measurements, we included plant material remote by all distinguished herbivores, both vertebrates and invertebrates. All values were energy equivalents (kJ), converted from biomass measurements using ideal conversion factors (Golley 1968). For productivity measurements, we considered only the nonwoody fraction of aboveground productivity - that is, net foliage production (NFP) - because woody production is largely inaccessible to herbivores. Plotting plant production against consumption revealed that terrestrial ecosystems fall into two groups that atomic number 18 distinguished by the intensity of herbivory (F.sub.1,78 = 88.2, P less than 0.0001 ILLUSTRATION FOR FIGURE 3 OMITTED). The maiden group includes low-herbivory habitats desert, tundra, temperate forest, tropical forest, TABULAR DATA FOR TABLE 1 OMITTED and littler grassland sites lacking large herbivores. The second includes the Serengeti and Yellowstone, which exhibit high herbivory rates. On average, herbivores removed 57% (SE = 3.4, n = 40) of NFP in the Serengeti and Yellowstone, whereas they removed only 9% (SE = 1.4, n = 40) of NFP in other terrestrial ecosystems. For example, only 10% (SE = 2.1, n = 14) of the aboveground production was consumed in temperate grasslands that lack large herbivores, showing that the remotion of migratory grazers dramatically affects the energy dynamics of grasslands. Slopes of the relationships did not differ statistically between the two groups (P greater than 0.10) and were greater than 1, indicating that the pr oportion of available primary production consumed increased as NFP increased for both groups of habitats. The low level of statistical distribution of samples around the regression line characterizing plant productivity and consumption in the Serengeti and Yellowstone grasslands suggests that the relationship describes a continuum from cool, temperate to warm, tropical crop ecosystems. Primary production is greater in... ...erlag. McNaughton SJ, Milchunas DG, Frank DA. 1996. How can net primary productivity be measured in grazing ecosystems? environmental science 77 974-977. Meagher M. 1973. The Bison of Yellowstone subject field Park. National Park Service Scientific Monograph Series 1. Washington (DC) United States department of Interior. Meagher M, Meyer ME. 1994. On the origin of brucellosis in bison of Yellowstone National Park A review Conservation Biology 8 645-653. Milchunas DG, Lauenroth WK. 1993. Quantitative effects of grazing on vegetation and soils over a global r ange of environments. Ecology 63 327-366. Morton JK. 1972. Phytogeography of the west African mountains. Pages 221-236 in Valentine DH, ed. Taxonomy, Phytogeography, and Evolution. New York Academic Press. Oesterheld, M, Sala OE, McNaughton SJ. 1992. center of animal husbandry on herbivore carrying capacity at the regional scale. nature 356 234-236. Peters RH. 1983. The Ecological Implications of Body Size. Cambridge (UK) Cambridge University Press. Prins HHT. 1996. Ecology and Behavior of the African Buffalo favorable Inequality and Decision Making London Chapman & Hall. Senft RL, Coughenour MB, Bailey DW, Rittenhouse LR, Sala