• Alpha diversity;
  • beta diversity;
  • evenness;
  • hierarchical partitioning;
  • latitudinal gradient;
  • macroecology;
  • Shannon diversity;
  • species richness

Abstract.  1. Knowing biodiversity patterns is a necessary first step for any conservation programme. The diversity patterns of many insect taxa are unknown in vast regions of desert and steppe regions of Asia. For the first time, we investigated the species diversity of ants across long environmental transects through two major steppe and desert biomes in Iran.

2. We sampled ants with a hierarchical sampling design across 10 degrees of latitude. We calculated species richness, Shannon diversity, and evenness, and partitioned species richness and Shannon diversity into their components, alpha (α) and beta (β), across five fine-to-broad spatial scales to assess their contribution to the gamma (γ) diversity of the region.

3. We found a total of 69 species of 17 genera of ants. Alpha species richness increased across latitudinal gradient, but beta species richness was not associated with latitude. Species richness and diversity measures increased across the hierarchical levels because of an increase of their beta components in both biomes. Beta values were significant at broad levels and to a large extent explained by distance. Species composition was determined at ecoregional level. Both biomes represented distinct faunal groups. Only at the highest level were species richness and Shannon diversity significantly higher in the steppe biome than in the desert biome.

4. Significant values of beta species richness and beta diversity across hierarchical levels suggest that ants are rather restricted to particular ecoregions or even localities in biomes, possibly making them vulnerable to extinction due to habitat disturbance and climate change.