Habitat structure shapes ant diversity in Amazonian white-sand ecosystems

White-sand ecosystems are one of the most distinctive vegetation types of the Amazon, but their arthropod diversity remains poorly studied. We compared ant assemblages of open white-sand campinas and white-sand forests in two regions in the northern Brazilian Amazon to examine the influence of habitat structure and location on taxonomic and functional diversity of these organisms. Alpha diversity of arboreal ants in white-sand campinas tended to be lower than in white-sand forests. In contrast, alpha diversity of ground-dwelling ants was similar in both habitats of the studied regions. The species composition of arboreal ants of white-sand campinas and white-sand forests was highly distinct between the study regions. In contrast, arboreal assemblages of these habitats were similar within each region. Species composition of ground-dwelling ants was strongly affected by habitat and region. Functional space of arboreal and ground-dwelling ants was also affected by region and habitat structure, with morphological traits related to vision (eye size), mobility (femur length) and prey manipulation (mandible lengths) filtered mainly by habitat independently of region. Our results highlight that structural complexity in white-sand forests promotes greater arboreal ant diversity, whereas ground-dwelling ants are more influenced by regional conditions, underscoring the complex interplay of ecological and historical factors in these habitats.