Diversity of ants (Hymenoptera, Formicidae) along a heavy metal pollution gradient: Evidence of a hump-shaped effect

Abstract

Abstract Ants, as indicators of ecological changes, are widely used in land management and environmental monitoring. At the same time, effects of industrial pollution are less known compared to many other stressors. We studied variations in habitat variables and ant diversity near the Karabash copper smelter (KCS) in Russia, in 2009 and 2014. Pitfall traps were set up at 10 birch forest sites (3 plots per site and 5 traps per plot) located to the north and south of the smelter within a 1–32-km range, with two samplings per season (June and August). The tree height, stand basal area, species richness of the field and moss layers, and the cover of the field layer decreased towards the smelter. The vegetation almost disappeared at the industrial barren close to KCS. In total, 21 ant species of 7 genera were registered. The highest species richness, diversity, and total occurrence of ants were observed in the transitional zone between moderately polluted forest habitats and industrial barren. Ant diversity and occurrence showed the same pattern in different years. Our results conform to the intermediate disturbance hypothesis predicting the greatest diversity at intermediate frequencies or intensities of disturbance or environmental change. Apparently, contaminant exposure affects ant communities near KCS indirectly, through habitat transformation. The study emphasizes the need for thorough planning of field studies of pollution effects on ants with examination of the full range of exposures. In addition, the nonlinear pattern of diversity and abundance of the ant community along the pollution gradients suggests caution, when assessing the magnitude of human impact and the state of ecosystems with ants as bioindicators.