Does interspecific competition from congeners cause the scarcity of Gerbillus henleyi in productive sandy desert habitats?

1. We tested the hypothesis that Gerbillus henleyi (de Winton 1903), the smallest species (10 g) of a pssamophilic guild in Israel, is scarce on relatively productive dunes of the Israeli desert, due to negative interactions from the common G. allenby i (Thomas 1918) and G. pyramidum (Geoffroy 1825). 2. The alternative hypothesis was that scarcity on sand resulted from the size of its naked hind feet, that do not allow efficient locomotion on sand. 3. Despite their naked soles the weight-bearing surface of G. henleyi feet carry less mass/area than those of any other species. 4. We measured interaction coefficients with the two common species using fieldmanipulation experiments in two enclosures. 5. Habitat usage of G. henleyi changed from significantly preferring the stabilized sand, when alone, to significantly using the semistabilized dune, when G. allenbyi was also present. 6. We also estimated the interaction coefficients and calculated the G. henleyi ’s isoclines competing with the two common gerbil species using a technique we developed elsewhere. 7. The stability analysis of the isoclines of G. henleyi competing with either G. allenbyi or with G. pyramidum suggests that stable coexistence occurs when G. henleyi is relatively scarce while the competitors are common. 8. Interspecific competition from either G. allenbyi or G. pyramidum accounts for 90·3% reduction in G. henleyi density, relative to when it is alone. 9. We concluded that the negative interactions from congeners was the major cause for the scarcity of G. henleyi on the relatively rich sand dunes of the Israeli desert.