Ants as geomorphological agents: A global assessment

Abstract Ants are abundant in most of the world's terrestrial environments. They are energetic, strong for their size, numerous, and socially cooperative. They play many geomorphologically important roles. In particular, they construct mounds and subterranean galleries, create patterned ground, play a role in bioturbation, affect vegetation cover and soil properties (such as infiltration rate) and influence runoff and erosion. They also play roles in biogeochemical cycling and rock and mineral weathering. Here, we review and reanalyse data collected from over 80 studies on ant contributions to geomorphology from around the world. The clearest manifestation of the geomorphological role of ants is found in their various constructions, such as mounds. There can be hundreds or thousands of mounds per hectare, with a median density of 125 ha−1 recorded in the studies reviewed. The longevity of these features varies and some are stable while others are highly erodible. The construction of mounds and galleries causes bioturbation (pedoturbation), a role which ants share with termites, worms and many mammals. A median rate of 1.5 t ha−1 a−1 is derived from the studies reviewed. Ants also produce patterned ground through their effects on vegetation. The relationships between ant activity and runoff and erosion are complex and not consistent. Bioturbation of soil, tunnelling activity, the construction of underground chambers, galleries and macro-pores, the removal and/or accumulation of organic material, and changes in vegetation cover, are all mechanisms by which ants might modify soil infiltration characteristics. Because of their effect on soil infiltration rates, sediment provision and on vegetation cover, ants can have a profound influence on runoff and soil movement on slopes. Only a modest amount of work has been done to investigate the role that ants play in rock weathering. Ants are greatly affected by human activities (especially land cover changes), and some geomorphologically-active species have proved to be highly invasive. The response of ants to future climate changes needs further investigation.