effects of harvester ants’ nest activity (messor spp.) on structure and function of plant community in a steppe rangeland (case study: roodshoor, saveh, iran)

harvester ants are known as one of the most renowned bio-disturbances in the arid and semi-arid ecosystems that affecte vegetation by collecting seeds and harvesting plants. it seems that physiognomy of plant association in steppe shrub land of roodshoor, saveh, iran has been highly changed by harvester ants’ activities that caused to conduct this research. the study was carried out on active and inactive nests and control site from june to august 2012. diversity indices and functional groups such as vegetative form, longevity, and photosynthesis type were analyzed as compared to criteria in three sites. results showed that richness, diversity, and vegetation cover in the ant colonies through increasing the annual forbs and rare species (campanula stricta and lepidium vesicarium) were more than the control site. for evenness index, however, there was no significant difference between the control and nest sites. in contrast, the function of plant community in the active nests due to the decrease of dominant shrub frequency of the area that is artimisia siberi by messor spp. was less than the control site. low diversity, richness, plant function, and high vegetation cover in inactive nests were also observed as the results of the presence and activities of the ants in the active nests. hence, the ant activities in the active and inactive nests can bring out micro sites with different plant associations so that regarding high density and quantity of the ant nests in all the area, it can decrease the key plants and change their functions. it therefore will debilitate the stability and function of this rangeland ecosystem.