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The existing literature proposes that productivity is responsible for biodiversity gradients in terrestrial habitats at large extents. At smaller spatial scales, however, other explanatory variables diminish or weaken the effect of the productivity predictor. These ideas have not been tested directly using ant communities. We studied a small extent of the geographical gradient of ant species richness in the Central Persian Desert ecoregion, Iran. We evaluated support for productivity and a series of alternative models with additional variables to examine determinants of ant species richness. Our results supported nine models. The productivity model and the tolerance-productivity model received the highest support. A curvilinear relationship was evident between ant species richness and productivity. In contrast to earlier work, we found that the ant species richness increased with increasing latitude. Our results suggest that in this desert ecosystem, plant productivity is the most important variable that controls ant species richness. Productivity did not completely explain the spatial gradient in ant species richness. At small spatial scales, other variables that co-vary with productivity have significant roles. (C) 2012 Elsevier Ltd. All rights reserved.