The cascading effects of removing ants on soil nutrients, soil invertebrates, and plants

Background/Question/Methods In temperate deciduous forests, ants disperse 20 to 50% of the total herbaceous flora. Thus, loss of native ants is a real and substantial threat for the plants they disperse. In southeastern deciduous forests, Aphaenogaster rudis ants disperse a disproportionate number of the forest herbs and can be considered keystone mutualists. We were interested in determining what effect removing A. rudis has on the spatial distribution of plants they disperse, on other soil invertebrates, and on soil nutrient dynamics. To test the effects of removing Aphaenogaster rudis ants on Hexastlylis arifolia, an understory herb dispersed by these ants, we experimentally removed A. rudis ants with a combination of AMDRO and a physical barrier with Tanglefoot from plots in Whitehall experimental forest in Athens, GA. Additionally, we measured the effects of removing A. rudis ants and reducing overall ant abundance on soil nutrients using in situ resin bags and soil arthropods Collembola and Acari with a combination of pitfall traps and leaf litter samples. Results/Conclusions We found a pronounced effect of removing A. rudis on the spatial distribution of H. arifolia seedlings, with significant clumping of seedlings near the parent plant in the ant removal plots and dispersion of seedlings in the control plots. We discuss the consequences of clumping for the survival of seedlings in the first and second years. We also found a large increase in total inorganic nitrogen in the ant removal plots compared to the controls in the first year of the study, but the effect disappeared in the second and third years of the study. We discuss the possible effects of ants on the soil invertebrate community, with possible implications for soil nutrient dynamics.