Pogonomyrmex spp. harvester ant colonies in the central Monte desert (Reserva de Ñacuñán, Mendoza, Argentina): environmental associations and spatial segregation (1999-2010)

Abstract

Seed-harvesting ants are dominant granivores in drylands. Three ecologically equivalent and phylogenetically related Pogonomyrmex species (P. inermis, P. mendozanus, P. propinqua), with similar life-history traits, overlapping diets and foraging periods, coexist at the habitat scale in the central Monte desert. We surveyed, mapped and followed for three consecutive activity seasons all active colonies within ~15 ha of the region’s main habitat (algarrobal, open woodland of Neltuma flexuosa and Larrea divaricata) protected from domestic grazing within the Ñacuñán biological reserve (Mendoza, Argentina). Then we mapped all Pogonomyrmex colonies appearing every three years (including after a multiyear drought) along 1.5 km segments of dirt roads crossing the algarrobal and associated them with gradients of soil permeability/texture and relative altitude. We analysed their distributions using spatial functions and models for uni- and bi dimensional point patterns to (1) describe their abundances, spatial distributions and population dynamics, (2) identify structural (distance to dirt roads) and edaphic (soil permeability and texture, local topography) factors that associate with their spatial patterns at different scales, and (3) examine the persistence and density-dependence of their intraspecific and interspecific spatial distributions.