Association between granivorous ants Pogonomyrmex pronotalis, P. rastratus and P. inermis, and roads in the central Monte desert

Abstract

Roads and roadsides represent a modified habitat markedly different from the original environment in which they are embedded. Conditions associated with roads can influence some insects’ population levels. In order to evaluate the degree of association between Pogonomyrmex pronotalis, Pogonomyrmex rastratus and Pogonomyrmex inermis, and roads in the central Monte desert we estimated colony density in the open woodland and in two roads. We also studied the activity and the diet of the three species in colonies located in both habitats. Pogonomyrmex pronotalis’ colony density was higher in the roads, Pogonomyrmex rastratus’ was lower and similar in both habitats and Pogonomyrmex inermis’ was very low in the roads and even lowerin the open woodland. Pogonomyrmex pronotalis’ activity was higher in roads and also higher than Pogonomyrmex rastratus’ and Pogonomyrmex inermis’. These two species presented similar levels of activity in both habitats. Diets were similar for the three species in the roads and in the open woodland. Seeds accounted for 80-100% of the items carried to the nests, and consisted mainly of grass seeds (more than 75% of the seeds). Seed species richness in the diets did not differ between habitats for any ant species. The proportion of some seeds in Pogonomyrmex pronotalis’ diet varied between habitats. Pogonomyrmex pronotalis was the only species that showed an association with roads. Its higher density there is probably due to favourable sites for nesting and establishment of colonies and its higher activity levels could be related to more suitable temperatures for this species. The results show that the location of the nest could only subtly influence the trophic ecology of these ants.