OOS 49-2 - Allometric scaling: Body size and fire-grazing interactions in an East African savanna

Friday, August 12, 2011: 8:20 AM
12A, Austin Convention Center
Ryan Sensenig1, Montague W. Demment2 and Emilio A. Laca2, (1)Department of Biological Science, Goshen College, Goshen, IN, (2)Plant Sciences, University of California, Davis, CA

Spatial scaling laws have taken a prominent role in both theoretical and empirical efforts to explain species coexistence whereby smaller bodied animals are predicted to perceive landscape grain at finer scales than larger bodied animals. Despite the longstanding assertion that spatial heterogeneity in grass quality and quantity is vital to perpetuating herbivore diversity in savanna systems, there remain few empirical examples testing such models. As part of a replicated large scale experiment in Laikipia, Kenya, we burned plots which varied in their extent (1, 9, and 81 ha) and grain (continuous and patchy). Using grids of dung transects we measured the use of these areas by a guild of large grazers ranging in size from hare to elephant.  


While we found burn preferences to be most strongly associated with body size, the size of burns significantly affected how grazers of varying body sizes used burns. Smaller bodied animals were able to focus on the smallest burn patches to a greater degree than larger bodied animals.  As predicted by scaling theory, smaller bodied animals had higher dung densities in the smallest patch sizes of highest quality, while the larger species either had uniform dung distributions or, as for the elephant, had highest dung densities in the largest patches of low quality. The one hectare burns received the highest total dung densities, but were more variable. On average, the nine hectare burns were maintained as grazing lawns longer than either the one or nine hectare burns. These findings suggest that the spatial attributes of burn patterns should be considered when trying to understand interactions between fire and grazing.

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