AbstractThe partitioning of gamma diversity into its alpha and beta components has been used to quantify the effects of natural habitat reduction on species diversity and distribution. Ant assemblages respond to anthropogenic changes, allowing their use as an indicator of biodiversity conservation in human‐modified landscapes. We investigated the responses of gamma, alpha, and beta diversity of ant assemblages to a forest cover gradient in southwestern Brazilian Amazon. Our prediction was that increasing forest cover would increase gamma diversity, which in turn is driven more by increasing beta diversity than alpha diversity along the forest cover gradient. Additionally, we expected that increasing beta diversity would be mainly driven by species replacement. We sampled ants within 12 circular areas (radius: 500 m) with different forest cover percentages in Chico Mendes Extractive Reserve, state of Acre, southwestern Brazilian Amazon. Gamma and beta diversity, but not alpha diversity, responded positively to the forest cover gradient. Additionally, species replacement was the main driver of beta diversity along the forest cover gradient. Areas with low levels of forest cover probably offer limited variation in habitats, resources, and conditions and, thus, harbor a low number of ant species that can easily disperse spatially and leading to species composition simplification. We recommend the use of diversity partitioning for indicator groups as an efficient way to monitor biodiversity and control the process of biota simplification at the human‐modified landscapes, showing the response of species diversity and distribution to human impacts.Abstract in Portuguese is available with online material.