Frank and McNaughton measured net aboveground primary productivity (ANPP), large herbivore consumption (C), and dung deposition (D), an index of nutrient flow from herbivores to the soil, in grassland and shrub-grassland habitat types on winter, transitional, and summer range, used by herds of elk (Cervus elaphus) and bison (Bison bison) in northern Yellowstone National Park. Data was collected during 1998, a year of drought and unusually high elk and bison populations, and 1989, a climatically near-average year, with fewer elk and bison. All three processes varied widely among sites, with an average of 45% ANPP being consumed by herbivores. There were positive spatial correlations between aboveground production and consumption and consumption and nutrient return to sites from herbivores. This suggest that native herbivores may steepen gradients of energy and nutrient fluxes in landscapes, beyond those gradients induced by topography alone. There was a 19% decrease in ANPP from 1988 and 1989, likely caused by death or injury to plants during the 1988 drought, which, in-turn, appeared to be responsible for reductions in elk and bison numbers, corresponding to declines in C and D.
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