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Dispersal ability is a key determinant of the realized species niche. Yet, whether dispersal ability influences environmental specialization and exerts a direct, indirect, or null effect on species’ tolerances is still unclear. Here, we ask whether and how dispersal ability can shape both the realized and fundamental niches. Focusing on plants, invertebrates, and vertebrates of the topographically complex Atlantic Rainforest, a top global biodiversity hotspot, we further evaluate how dispersal ability correlates with species range shifts in response to climate change. We find that high-dispersal species have broader thermal tolerances relative to low-dispersal taxa. When projected in geographic space, the data predict widespread upslope range shifts of the Atlantic Rainforest biodiversity with the intensity and direction depending on the species-specific trends depending on dispersal ability. These upslope movements, in turn, may negatively impact the native communities intrinsically associated with the Atlantic Forest mountaintops. Under the warmest climate scenario predicted for the end of the 21st century, the models project that those species with the lowest dispersal ability, particularly low-dispersible ectotherms, will be the most impacted by local extinctions. In turn, the wider thermal tolerance of high-dispersible species will reduce shifts in their geographical range due to climate change. Given the rapid rate of habitat conversion experienced by this and other landscapes worldwide, we argue that the smaller endurance of low-dispersible species to environmental changes deserves special attention, as dispersal ability appears relevant for biodiversity management in a warmer world, especially in threatened species-rich regions such as this.