The impact of ants on mineral soil properties and processes at different spatial scales

Soil dwelling ants are important soil engineers that have a large impact on the soil ecosystem. This is reflected in the alteration of soil properties by ants due to burrowing activities, the accumulation of organic matter and other nutrients in the soil, which, in turn, alters soil physical, chemical and (micro) biological processes. A review of recent literature on these fine scale soil changes resulting from ant activity is presented in this paper. However, ants do not only affect soil properties at the fine scale but also have effects at the hillslope and catchment scales with respect to surface hydrological processes and ecosystem functioning. At the finest scale, most studies showed changed soil textures, lowered bulk densities and increased infiltration where ant burrows or mineral mounds are prominent. Only a few studies investigated the effects of ants on soil properties such as soil structure and aggregate stability, which were improved by ant activity. Nutrients were generally considered to be concentrated in nests, and increased nutrient cycling involving microbial processes were reported. On a broader scale, the information on nest densities and patterns is crucial to understand the impacts of ants, but this information is scarcely available. It has been reported that the activity of ants increases the heterogeneity of soil infiltration rates and nutrient concentrations at the landscape scale, which in turn has consequences for the redistribution of sediments and nutrients by geomorphological and biotic processes. A hierarchical descriptive model focusing on dry land ecosystems is presented to incorporate small-scale ant activity into broader scale hillslope and catchment processes. However, this model has to be tested and more research is needed, especially on these broader scale aspects, to be able to fully understand the role of ants on the ecosystem and landscape scale.