Tapirus terrestris is the largest South American land mammal, with an extensive historical distribution and capable of occupying diverse habitats, and yet its populations have declined across its range. In order to provide baseline data on the conservation status of tapirs in the Atlantic Forest, we conducted a long-term study in one landscape, visited 93 forests, and received 217 expert reports over the 15-year study. We estimate that 2,665–15,992 tapirs remain in 48 confirmed populations, occupying 26,654 km2 of forest or 1.78% of its original range in the biome. Historically, hunting and deforestation were the main causes of decline, but today population isolation is the principal long-term threat. Vortex models indicate that 31.3–68.8% and 70.8–93.8% of the populations are demographically and genetically non-viable over the next 100 years, respectively, and that only 3–14 populations are viable when considering both variables. Habitat use data indicate that tapirs are adaptable to disturbed and secondary forests and will use diverse tree plantations and agricultural lands but hunting and highways keep populations isolated. Reserve staff report tapirs as common/abundant at 62.2% of the sites, and populations as stable and growing in 60% and 36% of the sites, respectively, and there is ample habitat in the biome for a population expansion, but overcoming the causes of isolation will be necessary for this to occur. Lack of adequate funding for protecting reserves is a chronic threat throughout the biome, especially in federal and state/provincial reserves, and increased funding will be necessary to implement effective conservation plans.
