Ants
Ants are found in most soils throughout the world, but are more diverse in countries such as Australia, Brazil, Indonesia, China and Mexico (> 1000 species) and a higher percentage of endemic species in places like Australia (87%), while the highest percentage of the world‘s ant species are found in neo-tropical, indo-Australian and afro-tropical regions. Undoubtedly the construction of ant nests sometimes to 1 m in depth has impacts on soil through the excavation and movement of soil from lower horizons to the soil surface. This activity is called bioturbation, and despite it’s potential for soil mixing and profile alteration it has been studied sporadically over the decades[1],[2].
Ants are generally resilient to soil disturbance and can be found in abundance in farmed soil, although less diverse than the naturally vegetated environment[3],[4],[5]. Their role in supporting soil functions is to create channels and macropores from soil surface to deeper depths or lateral channels that are shallow, depending on type and permanency of the nest structure[6]. This has an important role for the function Water Regulation and Water Purification. Ants have a diverse dietary range but seed collecting ant species are more commonly found in grazing lands. The impact of ant activity on chemical soil properties and nutrient cycling is studied for select ant species that build prominent and permanent nest structures[7].
Identification of ants to species level is still problematic where taxonomic keys are not accessible, and techniques for assessing ant activity and composition have traditionally relied on pitfall trapping, over an extended time period, which does not capture in situ ant activity in the soil[8]. Hence connecting ant activity and species to soil function requires other techniques such as baiting, mapping and identification of ant nests in situ.
There are several types of ant databases that have global reach, one on ant traits and species (GLAD – The Global Ants Database)[9] which also has links to other useful taxonomic tools such as AntWeb. These tools are linked to a location but offer limited data related to site condition and the effects of soil disturbances related to agricultural management and environmental impact in natural ecosystems. AntWiki on the other hand has a range of information from ant identification and ant ecology, life history and behavior, but limited quantification of ant’s role in soil functions.
[1] Lobry de Bruyn LA and Conacher AJ. 1990. The role of termites and ants in soil modification - a review. Soil Research 28: 55-93.
[2] Lobry de Bruyn LA and Conacher AJ. 1994. The bioturbation activity of ants in agriculturally and naturally vegetated habitats of semi-arid environments. Australian Journal of Soil Research 32: 555-570.
[3] Lobry de Bruyn LA. 1993. Ant composition and activity in naturally-vegetated and farmland environments on contrasting soils at kellerberrin, western australia. Soil Biology and Biochemistry 25: 1043-1056.
[4] Nkem NJ et al. 2020. The effect of increasing topsoil disturbance on surface-active invertebrate composition and abundance under grazing and cropping regimes on Vertisols in North-West New South Wales, Australia. Insects 11.
[5] Tuma J et al. 2019. Logging of rainforest and conversion to oil palm reduces bioturbator diversity but not levels of bioturbation. Applied Soil Ecology 144: 123-133.
[6] Lobry De Bruyn LA and Conacher AJ. 1994. The effect of ant biopores on water infiltration in soils in undisturbed bushland and in farmland in a semi-arid environment. Pedobiolgia 38: 193-207.
[7] Wang S et al. 2018. Feeding-strategy effect of Pheidole ants on microbial carbon and physicochemical properties in tropical forest soils. Applied Soil Ecology 133: 177-185.
[8] Lobry De Bruyn LA. 1993. Defining soil macrofauna composition and activity for biopedological studies: A case study on two soils in the Western Australian wheatbelt. Australian Journal of Soil Research 31: 83-95.
[9] Parr CL et al. 2017. GlobalAnts: a new database on the geography of ant traits (Hymenoptera: Formicidae). Insect Conservation and Diversity 10: 5-20.
Text by Dr. Lisa Lobry De Bruyn, School of Environmental and Rural Sciences at the University of New England