Alteration of arid lands’ vegetation may lead to constant changes in the soil in a way that for many years can not be returned to its original condition. Reproductive succsess and dispersal of plants, to a high extent, depends on their ability for seed dispersal. Myrmecochory is an important factor in determining the distribution composition and species diversity of vegetation communities particularly in arid land ecosystems. We studied the potential seed dispersal by harvester ants ( Messor .) and Persian gazelle ( Gazella subgutturosa ) in Kolah-Qazi National Park, central Iran. The study conducted for six months (April, May, June, July, October, November) in 2013. In each month, 30 ant nests where no gazelle dung was around it and 30 ant nests where gazelle dungs were detected on them were randomly selected across the study area. From each ant nest, a soil sample with a depth of 5 cm was taken. 60 habitat sites including 30 independent replicates for ant nest with gazelle dung and 30 independent replicates for ant nest without gazelle dung were selected. Samples were dried in a dark room by exposing to open air and then from each a sample was taken and kept in refrigerator for two months for cold stratification treatment. Seed content of dung samples were determined in greenhouse germination experiments over a period of 8 months. In total, 124037 seedlings from 63 plant species and 21 families were germinated from ant nest soil samples. Of these, 52 species were forb, 9 species were grass and 2 species were shrub. Although the species richness of grasses were low, but they constituted about 52% of the total germinated seeds. In May, June and July, the density and richness of seeds were higher in ant nest sites without gazelle dung. In contrast, in April, September and Octoberthe density and richness of seeds were higher in ant nest sites with gazelle dung. Seedlings grown from soil samples of ant nests with gazelle dung showed higher species richness, while those resulted from soil samples of ant nests without gazelle dung had higher species density. The ant nests were divided into four groups based on their seed species richness as resulted from principal component analysis and cluster analysis, while the months located into three clusters: April and May; June and July; and September and October. Given that most of plant species recorded in the park regenerate by seeds, and that seeds of different plant species dispersed by harvester ants, mirmecochory may play an important role in vegetation dynamics and conservation of semi-arid steppe rangelands. Keywords :Seed germination experiment, harvester ants, ant nests’ seed content, arid ecosystems.
