Effects of nest building by the dominant hunting ant, Ectatomma sp. 2 (E. ruidum complex), on Andean coffee plantations

摘要

Soil removal by ants when building or adapting their nests generates ecological changes within the soil and on its surface, impacting both soil physical properties and plant growth. Ectatomma sp. 2 (E. ruidum complex) is a dominant hunting ant in numerous neotropical agricultural systems; however, its bioturbation impact on agroecosystems of economic importance, such as coffee, has not been studied. We evaluated it on coffee seedlings in Andean plantations of Colombia. Sixty colonies of this ant (30 in sun coffee, 30 in shaded coffee) were added within enclosed experimental units (EUs) containing coffee seedlings, and compared with their respective controls without ants. On average, dry soil removal by colony was 104.4 g during the two months experimental period (1.6 g day(-1) colony(-1)), 13 times higher than in controls. A conservative estimate of their global bioturbation impact was calculated at between 59.3 and 203.1 kg dry soil ha(-1), considering only two months of digging activity year(-1) colony(-1), a likely underestimation of the actual digging activity of this species. Positive effects of the presence of ants were found on several plant growth variables and on soil microporosity in shaded coffee plantations. Taking into consideration only the 14 colonies that were fully active until the end of the experiment, dry soil removal was on average 228.8 g (3.5 g day(-1) colony(-1)) during the two months experimental period and coffee seedling growth in these EUs was significantly higher than in controls, indicating that, at the global scale, our bioturbation estimate could be higher under less restricted natural conditions and higher nest densities as found in other regions. Ectatomma ruidum sp. 2 appears as a functional agent in agroecosystems due to its ubiquity and its high bioturbation impact during the nest excavation period of activity, providing support services in agroecosystems and neotropical natural systems.