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Since broad-scale patterns of richness are correlated with climatic variables, a central question is whether climate could represent a primary explanation for richness gradients and specifically, how different components of the water-energy dynamic can contribute to regional richness patterns. In the sandy dunes of Israel, where mean annual precipitation rises sharply from 30 to 600 mm within a distance of only 360 km, precipitation and temperature were tested as explanatory variables of the ant-species richness pattern. Moreover, since two biogeographic regions, the Mediterranean and Saharo-Arabian, intersect within the study area, the hypothesis that two distinctive ant species assemblages exist on either side of the biogeographic cross-point was examined. Annual precipitation and ant-species richness showed a significant unimodal pattern, while no correlation was found between temperature and ant-species richness. Cluster and detrended correspondence analyses suggest that the intersection between the two biogeographic regions does not act as a biogeographic barrier. Moreover, the highest ant-species richness was not found in the high-productivity region but in the intersection between the two biogeographic regions, where resource heterogeneity could be high. This suggests that the observed unimodality between ant-species richness and precipitation could be the result of the intersection between these biogeographic regions. (C) 2009 Elsevier Ltd. All rights reserved.