However, in many studies, it is implied that it is primarily the transport engineering role of harvester ants that accounts for the higher density of plants associated with the nests, and this has indeed been shown to be the case for a few individual species (e.g. Sánchez et al., 2006). It is also conceivable that the substrate itself acts as a trap for seeds from non-nest areas due to its coarse nature, which could also be amplified by the factthat seeds ofindividuals already inhabiting the refuse zone will be dispersed to the same area without the intervention of ants.