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The Ecology of the Earth's Grazing Ecosystems The Ecology of the Earth's Grazing Ecosystems Douglas A. Frank; Samuel J. McNaughton; Benjamin F. Tracy BioScience, Vol. 48, No. 7. (Jul., 1998), pp. 513-521. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199807%2948%3A7%3C513%3ATEOTEG%3E2.0.CO%3B2-E BioScience is currently published by American Institute of Biological Sciences. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/aibs.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact [email protected]. http://www.jstor.org Mon Oct 29 19:30:32 2007 The Ecology of the Earth's brazing Ecosystems Profound functional similarities exist between the Serengeti and Yellowstone Douglas A. Frank, Samuel J. McNaughton, and Benjamin F. Tracy s recently as 150 years ago, the size, possesses almost four times most of Earth's grasslands The grazing ecosystem the ungulate species, and has ap- .supported large migratory proximately 52 times the number of populations of hoofed herbivores be- is among Earth's ungulates as YNP (Table 1). longing to the Artiodactyla, Perisso- There are several additional dif- dactyla, and Proboscidea-that is, most endangered ferences between the Serengeti and ungulates. These herbivores included YNP. First, the Serengeti is a slop- bison (Bison bison) on the North terrestrial habitats ing, broad plateau covered primarily ~meric'anplains, saiga antelope (Saiga by grassland and savanna, whereas tatarica) on the Eurasian steppe, YNP is a mountainous reserve occu- wildebeest (Connochaetes taurinus) be markedly different. We contend pied by coniferous forest (80%)and and zebra (Equus burchelli) on the that the Serengeti and YNP are ex- grassland (20%),the latter being the African savanna, and the ecologi- tant members of a once-widespread focus of this discussion. Serengeti cally equivalent kangaroos (Macro- ecosystem type that we refer to as a grass species all possess the C, pho- podidae) on the Australian savanna. "grazing ecosystem." This ecosys- tosynthetic pathway, whereas grasses As a result of the ~ost-industrial tem is distinguished from other habi- of YNP all have the C, pathway. global expansion of cropland and tats by its prominent herbivore-based Moreover, the Serengeti and YNP cattle ranching, most grasslands food web and by the extent to which support warm, tropical grasslands grazed by Pleistocene megaherbi- ecological processes are regulated by and cool, temperate grasslands, re- vores were eliminated. Today, they dynamics within that food web. spectively, which are about as dis- are restricted to the world's few large similar climatically as any two grass- grassland reserves that protect all Structural and land ecosystems on Earth (Figure 2). seasonal ranees of the animals. In Nevertheless, within the constraints this article, ke describe profound climatic differences imposed by some of these differ- functional similarities between two The Serengeti and YNP have been ences, the ecosystems exhibit a high of the most celebrated of these re- described as being dissimilar largely degree of functional similarity. maining habitats, the Serengeti eco- because of their structural, bound- system of east Africa and Yellowstone ary, and climatic characteristics Energy dynamics of National Park (YNP) of the North (Berger 1991). Annual movements grazing ecosystems American intermountain west, which of the major ungulate species delin- previously have been considered to eate the Serengeti ecosystem, of which Grazing ecosystems support more 85% is protected in the Serengeti herbivore biomass than any other Douglas A. Frank (e-mail: dafrank@ National Park, Masai Mara Game terrestrial habitat (Sinclair 1975, mailbox.syr.edu) is an assistant professor, Reserve, and numerous other, smaller Detling 1988, McNaughton et al. SamuelJ.McNaughton (e-mail: sjmcnaug@ game reserves. By contrast, the 1989, 1991, Huntly 1991).A func- mailbox.syr.edu) is a professor, and Ben- boundaries of YNP were originally tional consequence of this disparity jamin F. Tracy (e-mail: [email protected]) was drawn to protect the area's thermal in trophic structure emerges by com- a graduate student in the Department of features, with little regard to the paring the relationship between Biology, Syracuseuniversity, Syracuse, NY 13244-1220.They study the effects of large migratory patterns of animals. Con- aboveground production and herbi- herbivores on grassland processes in the sequently, ungulates regularly mi- vore consumption in the Serengeti Serengeti and Yellowstone National Park. grate across park boundaries to habi- and Yellowstone ecosystems with O 1998 American Institute of Biological tats that are not protected (Figure 1). that in other terrestrial ecosystems Sciences. The Serengeti is almost three times (Figure 3). For consumption measure- July 1998 513 w -- Montana ) Western Corridor \ \ ) Forest 30 I 50 100 150 200 250 Mean Annual Precipitation (cm) Figure 2. Approximate placement of the Serengeti and grassland habitat of Yel- lowstone National Park in Whittaker's (1975)climate-biome diagram. The area designated as grassland includes shrub- Figure 1. The locations of the Serengeti and Yellowstone National Park (YNP)in Africa grassland, savanna, and open woodland and North America, respectively. The boundaries of both ecosystems (dashed lines) are habitat. The Serengeti and Yellowstone are determined by the migratory patterns of ungulates. Isopleths of mean annual precipi- climatically disparate grassland ecosystems. tation are shown for the Serengeti, and isopleths of elevation are shown for YNP. These variables are the principal environmental factors controlling habitat variability and consumed increased as NFP increased seasonal migrations (denoted by arrows) in the two ecosystems. for both groups of habitats. The low level of dis~ersionof ments, we included plant material re- est, and small grassland sites lacking samples around the regression line moved by all important herbivores, large herbivores. The second includes characterizing plant productivity and both vertebrates and invertebrates. the Serengeti and Yellowstone, which consumption in the Serengeti and All values were energy equivalents exhibit high herbivory rates. On av- Yellowstone grasslands suggests that (kJ), converted from biomass mea- erage, herbivores removed 57% (SE the relationship describes a con- surements using standard conversion = 3.4, n = 40) of NFP in the Serengeti tinuum from cool, temperate to factors (Golley 1968). For produc- and Yellowstone, whereas they re- warm, tropical grazing ecosystems. tivity measurements, we considered moved only 9% (SE = 1.4, n = 40) of Primary production is greater in the only the nonwoody fraction of NFP in other terrestrial ecosystems. Serengeti (average = 11,118 kJ . m-2 aboveground productivity-that is, For example, only 10% (SE = 2.1, n yr-I, SE = 978, n = 28) than in net foliage production (NFP)-be- = 14) of the aboveground produc- Yellowstone (average = 3168 kJ . cause woody production is largely tion was consumed in temperate m-2 yr-', SE = 530, n = 12), most unavailable to herbivores. grasslands that lack large herbivores, likely because of a combination of Plotting plant production against showing that the removal of migra- several factors: solar radiation and consumption revealed that terrestrial tory grazers dramatically affects the temperature are higher in the tropi- ecosystems fall into two groups that energy dynamics of grasslands. cal system; some areas of the are distinguished by the intensity of Slopes of the relationships did not Serengeti receive more precipitation herbivory (F1,78= 88.2, P < 0.0001; differ statistically between the two (range= 40-100 cmlyr) than Yellow- Figure 3). The first group includes groups (P > 0.10) and were greater stone (range= 40-75 cmlyr); a greater low-herbivory habitats: desert, tun- than 1, indicating that the propor- proportion of precipitation results dra, temperate forest, tropical for- tion of available primary production in runoff in the Yellowstone ecosys- tem; and the C,photosynthetic path- Table 1.Properties of the Serengeti ecosystem and Yellowstone National Park (YNP). way of the Serengeti vegetation con- fers greater water-use efficiency than Property Serengeti YNP the C, photosynthetic pathway of Size (km2) 26,000 9018 Yellowstone plants. Consumption Ungulate species 31 8 also is higher in the Serengeti (aver- Ungulate number 2,137,000 40,600 age = 7737 kJ . m-2. yr-', SE = 911) Vegetation structure Savanna and grassland Coniferous
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