ECOLOGY/EVOLUTION

In the Short Grass

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Science  15 Oct 2004:
Vol. 306, Issue 5695, pp. 375
DOI: 10.1126/science.306.5695.375a

The unpredictability of the movements of groups and populations of grazing animals causes difficulties for the conservation and management of their rangelands. The shifting mosaic of forage production, grazer occupation, and predator distribution depends on a web of climatic, physiological, and behavioral variables — factors that tend to be measured and modeled at different spatial and temporal scales. By linking behavioral models and 2-year spatial censuses over 1600 km2 of the Serengeti plains, Fryxell et al. attempt to predict the spatial distribution of Thomson's gazelles in East African grasslands. They first compared the power of several different foraging models examining the contribution to the animals' relative fitness of hourly or daily food (energy) intake. Daily energy intake was the best predictor of gazelle's occupation of short-grass patches. They then compared seven further models of animal movements and found that gazelles move to neighboring patches with a probability that is proportionate to the potential energy gain. These results help explain why populations of grazers can require such large areas, and they will help in the formulation of management strategies to ensure long-term success. — AMS

Ecology 85, 2429 (2004).

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