Aim To assess how community diversity and phylogenetic context shape plant thermal tolerance strategies along a tropical elevational gradient, and to determine whether biotic context explains variation in thermal niches beyond elevation alone. Location Brazilian Atlantic Forest. Time period 2023–2024. Major taxa studied Vascular plants, with emphasis on the bromeliad Pitcairnia flammea and co-occurring monocots, dicots, and ferns. Methods We surveyed plant assemblages across seven sites spanning sea level to ~2,200 m elevation. Community diversity, species cover, and phylogenetic structure were quantified for each assemblage. Photosynthetic heat and cold tolerance (T50) and leaf functional traits were measured for P. flammea populations and dominant sympatric species. Phylogenetic analyses, principal component analysis, and AIC-based model comparisons were used to assess the relative roles of elevation, diversity, and phylogenetic context in shaping thermal strategies. Results Cold tolerance and leaf area showed strong phylogenetic conservatism across taxa, whereas heat tolerance exhibited little phylogenetic structure. Mid-elevation assemblages, characterized by peak species richness, showed greater divergence in thermal tolerance among species. In contrast, P. flammea populations displayed their broadest thermal tolerance at high elevations, coinciding with high monocot diversity and phylogenetic clustering, despite harsher abiotic conditions. Lowland populations were abundant but exhibited reduced heat tolerance in assemblages with lower representation of closely related taxa. Overall, community diversity and phylogenetic structure explained variation in thermal strategies better than elevation alone. Main conclusions Biotic context plays a central role in structuring plant thermal niches along tropical elevational gradients. Integrating community composition and evolutionary history with abiotic gradients is essential for interpreting elevational patterns and predicting species responses to climate change in species-rich tropical systems.

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.