Effect of harvester ants (Pogonomyrmex spp.) on the soil seed bank near their nests in the Monte desert, Argentina

PIRK, G.I.; LOPEZ DE CASENAVE, J.

Bariloche

Congreso; VI Southern Connection Congress; 2010

Southern Connection

Granivorous animals can have a significant impact on soil seed abundance. As central-place foragers, harvester ants may reduce seed reserves more drastically near their nests. In the Monte desert, Argentina, ants of the genus Pogonomyrmex show relatively high seed removal rates during their foraging season (late spring-early autumn) and concentrate their consumption on a few grass species. The aim of this study was to quantify soil seed abundance of the most consumed species at different distances from the nest along the foraging season. Soil seed abundance was measured in bare soil and litter on three occasions (October, December and April). In October, no distance gradient in seed abundance was detected, probably because of the low level of seed consumption at the beginning of the season. In December Stipa ichu seeds were less abundant in the litter close to the nest entrance. These seeds are the first grass seeds to be produced and ants usually consume them when other grass seeds are still scarce. In April, seed abundance in the litter was lower near the nest, probably as a consequence of the high consumption from midsummer on. The lack of an effect in bare soil could be due to the lower seed harvest of ants in this substrate or to the high horizontal redistribution of seeds in exposed sites. This study suggests that the presence of Pogonomyrmex colonies increases the heterogeneity of the soil seed bank in the Monte desert, eventually affecting vegetation patterns.