Abstract
Environmental impact studies often involve monitoring and using bioindicators to evaluate the restoration stage of impacted areas. We aimed to assess ant assemblages’ response to the ecological succession of previously disturbed areas in the Brazilian Amazon. We sampled epigeic ant assemblages in five bauxite mining areas, representing different restoration stages, and compared them with two pristine areas. We also compared trends in species richness at the same mine site investigated 14 years earlier. Ten pitfall traps and four Winkler samples of litter were taken along a 100-m transect in each area. We expected that ant species richness would increase with the amelioration in habitat condition (i.e., environmental surrogates of ecological succession, including litter depth, soil penetrability, the circumference of trees, the distance of trees to adjacent trees, and percentage of ground cover). We also compared the efficacy of both sampling methods. Due to more significant sampling effort, pitfall traps captured more ant species than Winkler sacks. However, Winkler samples’ addition allowed the collection of more cryptic species than by pitfall traps alone. We sampled a total of 129 ant species, with increases in ant species richness in more mature rehabilitation. Nevertheless, similarity analysis indicated a significant difference between ant assemblages of rehabilitated areas and pristine ones. Assemblages differed mainly by the presence of specialist and rare species, found only in pristine plots. Rehabilitated areas exhibited a significant increase in tree circumference as they reached more ecologically advanced stages, which contributed to increasing ant species richness. These trends and comparison with the earlier study indicate that although there are favorable increases in ant species richness, in terms of species composition, rehabilitated areas were far from achieving an ant assemblage composition or environmental status that closely resembles pristine areas.
Highlights
Brazil has become an important global trader of raw materials in the mineral sector, including bauxite, whose main reserves occur within the Legal Amazon (IBRAM 2010)
During our study period, the maximum and minimum temperatures in Porto Trombetas were respectively 32.5°C and 22.0°C; 476.5 mm of rainfall fell in May 2006, and 133.0 mm of rain fell in June 2006 (CPTEC / INPE)
Mayaponera constricta and Pachycondyla harpax were widely distributed in the rehabilitated plots but were found less frequently in pristine areas
Summary
Brazil has become an important global trader of raw materials in the mineral sector, including bauxite, whose main reserves occur within the Legal Amazon (IBRAM 2010). Detailed studies on recolonization of soil biota and distribution of species after mining operations can provide management programs with more robust information on how ecological processes evolve to achieve a sustainable stage (Kollman et al, 2016). In this case, a common approach is the use of bioindicators that can reflect the restored sites’ environmental conditions (Ribas et al, 2012; Schmidt et al, 2013, Donoso, 2017)
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