Medium to large-bodied terrestrial mammals have a wide diversity of forms, life history, behaviour, physiology, and consequently a high diversity of ecological roles played in natural and human-modified ecosystems. Ecological functions such as seed dispersal, seed predation, pollination, population control, nutrient cycling and transport, and ecosystem engineering help maintain tropical ecosystems and regulate species diversity. Ecosystem engineers are species that by their presence and/or activity alter the biotic and abiotic environment, modulating the availability of resources and modifying habitat structure for other species. The way organisms can affect each other is diverse and occurs mainly through ecological interactions such as predation, competition and commensalism or facilitation, which in turn encompass several ecological processes such as pollination, dispersal, herbivory and prey control. The first chapter of this thesis assessed the role of Priodontes maximus (Giant Armadillo; tatu canastra) as an ecosystem engineer in southwestern Amazonian forests. Our results showed that a wide diversity of terrestrial vertebrates benefit from P. maximus burrows. Sites with high local diversity tend to increase the amount of interactions between vertebrate species and armadillo burrows. In addition, we identified the purpose for which most vertebrates use the burrows of this large excavator, showing that the interaction established in the burrows is broadly and strongly connected for a variety of purposes. In the second chapter of this thesis, I examine how medium and large-bodied mammals can interfere with the regeneration process of man-made treefall clearings formed by low-impact selective logging in southwestern Amazonia. Based on the relative abundance of species, damage to artificial seedlings was measured within both clearings and otherwise comparable shaded-understorey environments. Based on the results, I can infer that medium and large mammals affect seedling recruitment process in clearings. The impact of mammal-induced seedling mortality (via trampling and/or herbivory) is much greater within natural and logging clearings than in closed understorey environments.