Dispersal Ability Reduces Thermal Specialization and Prevents Climate-Driven Extinctions in a Neotropical Rainforest.

Dispersal ability is a key factor in determining a species' realized niche. However, it remains unclear whether dispersal ability directly, indirectly, or neutrally affects environmental specialization and species' tolerance ranges. Here, we investigate whether, and how, dispersal ability shapes both the realized and fundamental niches. Focusing on plants, invertebrates, and vertebrates in the topographically complex Atlantic Rainforest-one of the world's top biodiversity hotspots-we also assess how dispersal ability correlates with species' range shifts in response to climate change. Our findings indicate that high-dispersal species exhibit broader thermal tolerances compared to low-dispersal taxa, which are often restricted to higher elevations. Projected across geographic space, these data forecast a concerning scenario for species with limited dispersal abilities-particularly low-dispersal ectotherms-which are expected to face the highest risks of local extinction, even under the milder climate projections for the end of the 21st century. In contrast, species with broader thermal tolerances and higher dispersal capacities are expected to undergo reduced range shifts in response to climate change, particularly under the milder climate projection. Therefore, while the milder projections already indicate high extinction rates in the highlands, the warmest future scenario exacerbates this trend by predicting a substantial influx of high-dispersal species moving upslope (and southward) that are also expected to be locally affected by climate change. These upward movements are expected to negatively affect native communities closely tied to the forest's mountaintop ecosystems. Given the rapid habitat conversion affecting this and similar landscapes globally, we emphasize the importance of prioritizing low-dispersal species in biodiversity management. Our results highlight the critical role of dispersal ability in species' resilience to ongoing climate warming, especially in biodiversity-rich but threatened regions like the Atlantic Rainforest.