Species Extirpation and Colonization Reveal Mixed Homogenization and Differentiation Across Terrestrial Taxa After One of the World's Largest Tailings Dam Failures.

In 2015, the failure of the Fundão tailings dam released ~45 million m3 of liquefied tailings into Brazil's Doce River basin, contaminating ~670 km of waterways to the Atlantic Ocean. However, the biodiversity consequences of this event for terrestrial organisms remain poorly understood, particularly across multiple terrestrial taxonomic groups and through time. We assessed how direct and indirect exposure to mine tailings affected the abundance and diversity of plants, vertebrates (anurans and birds), and invertebrates (ants, bees, beetles, and butterflies) in a 4-year monitoring period from 2022 to 2025. As reference sites, we selected areas that had not been affected by mine tailings but were located sufficiently close to the impacted sites to allow organisms to move among them. We quantified effects on the number of individuals and species and partitioned spatiotemporal β-diversity into colonization and extirpation components to evaluate consequences for biotic homogenization and differentiation. Directly impacted sites exhibited stronger reductions in abundance and unstandardized richness than indirectly impacted and reference sites, but responses varied among taxonomic groups and depended on whether change was evaluated using incidence (species identities) or abundance (dominance). Overall, mine tailings effects operated through two nonexclusive pathways: taxon-specific changes in population size and shifts in community composition driven by altered extirpation and colonization. Across groups, impacted landscapes could simultaneously exhibit differentiation via site-specific losses and homogenization via dominance shifts. These results show that mine tailings can restructure biodiversity along multiple dimensions, emphasizing the need to evaluate abundance, composition, and turnover processes when assessing impacts and recovery in diverse ecosystems.