Mountain ranges are important centers of biodiversity around the world. This high diversity is the result of the presence of different soil types and underlying bedrock, a variety of micro-climatic regimes, high topographic heterogeneity, a heterogeneous and complex vegetation cline, and a dynamic geo-climatic history. Neotropical research on mountains has focused on the Andes, while other mountain ranges are lacking in biodiversity and biogeographic studies. However, the non-Andean mountains comprise important elements of the South American relief, are home to a substantial proportion of Neotropical species, and exhibit a complex and reticulate history of diversification of their biota. Here, we provide a brief review of the biological and biogeographical importance of the major non-Andean South American mountain ranges, discussing their role for diversification and maintenance of Neotropical biodiversity. We focus on six regions: the Serra do Mar Range, the Mantiqueira Mountains, the Espinhaço Mountains, the Northeastern Highlands, the Central Brazilian Highlands, and the Pantepui region. We summarize the main geophysical and biotic characteristics of each mountain range, as well as key results from phylogenetic studies, the fossil record, and studies tackling biogeographical patterns of diversity, richness, and endemism. Moreover, mountain biodiversity studies can incorporate not only environmental data, but also information on more recent man-made landscape shifts. Here, we provide an example of how human population density interacts with climate and species traits to explain richness patterns in one group of montane organisms particularly vulnerable to environmental changes: anuran amphibians. Our results and the evidence published to date indicate that the Neogene and Quaternary were pivotal periods of Neotropical diversification for many terrestrial taxa, promoting endemism in non-Andean mountains. In general, all non-Andean mountain ranges have high levels of species richness and endemism as compared to their surrounding lowlands. Biotic interchange among them, the Andes, and their surrounding biotas has been intensive over tens of millions of years, greatly contributing to the outstanding levels of Neotropical biodiversity observed today. Despite their vast and understudied biodiversity, mountain ecosystems are fragile, facing severe challenges in the face of climate change, habitat loss, and extinctions. Efforts to better understand and protect South American mountain ecosystems are urgently needed.
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