Environmental drivers of diversity in Subtropical Highland Grasslands

• Altitude explained the delimitation of diversity areas of SHG.
• High linear correlation between precipitation variables and species diversity.
• Diversity is correlated with niche stability.
• The stability of niche and diversity were higher in the southeast.
• Two of the areas are important sites for study and conservation.

The aim of this study was to identify major bioclimatic variables associated with the diversity patterns of plant genera and the contribution of elevations in highly diverse areas of the Subtropical Highland Grasslands (SHG), which form mosaics with Araucaria forests. We selected three plant genera that have diversified, in part, within the Neotropical SHG: Adesmia (Fabaceae) and Calibrachoa and Petunia (Solanaceae). We delimited the major high elevation areas of the region and calculated the taxonomic diversity for these taxa in each area. Ecological Niche Models (ENMs) were used to predict the distribution of each taxon and to project it to the Last Glacial Maximum (LGM), allowing searching for stable areas. Those stable areas were then compared to areas with high diversity levels. We explored the spatial occurrences and the multivariate contribution of environmental factors to differentiate among the Araucaria forest and the SHG. Finally, we examined the correlations between the environmental variables and the molecular and taxonomic diversity. Niche stability was directly linked to diversity and positively correlated with altitude. Although some niche aspects differed subtly, the predicted distributions of grassland and forest taxa were not different at larger scales. Two of the four studied areas were suggested by the ENMs to be high-relevant sites for conservation studies and the maintenance of diversity.

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