The size-grain hypothesis: A phylogenetic and field test

1. The size-grain hypothesis predicts that environmental rugosity results in positive allometric scaling of leg length on body length because of changes in locomotion costs. 2. The scaling of leg length and body length in ants was re-examined using phylogenetic independent contrast methods, and the allometric relationship found by Kaspari and Weiser (Functional Ecology, 13, 530-538, 1999) was supported. 3. The size-grain hypothesis was tested further by comparing the body sizes of ants from areas of contrasting habitat complexity in two different savanna habitats. No support for the size-grain hypothesis was found. Small body size classes were no more speciose in the rugose than in the more planar environment, and small ants were more abundant in the planar environment.