Projections on global climate disruption are temperature increases, rainfall reductions in dry areas and the opposite on wet areas, and more extreme climate events. How these processes affect biodiversity known for taxonomic diversity (and less on functional diversity) of plants and for animals is emerging. Most studies on mammals focus on temperate habitats, lack long-term demographic data and rely on bibliographical traits. The causes of tropical mammal taxonomic and functional diversity are unknown. We compared taxonomic and functional richness and diversity, abundance and biomass against a neutral model, temperature and rainfall in two contiguous and distinct (upland and arroyo) tropical dry forests. Rainfall (seasonal and atypical) affected small mammals more in the harsher conditions of the upland forests than in the arroyo forest, a richer, more diverse, and stable habitat. These findings stress the threats of global climate disruption on the mammals inhabiting tropical dry forests, the most endangered terrestrial ecosystems on Earth.