Looking similar but all different: Phylogenetic signature of Brazilian rocky outcrops and the influence of temperature variability on their phylogenetic structure

Abstract

Abstract Old, climatically buffered, infertile landscapes (OCBILs) have a disjunct yet wide distribution worldwide. Old lineages, rare and geographically restricted species, generally characterise these landscapes. Although the last decade provided evidence supporting the OCBIL theory, many studies are biased towards local scales, woody plants and specific OCBILs. Therefore, broad‐scale investigations across different types of OCBILs are needed. We used 5186 flowering plant species (woody and herbaceous) distributed across 129 rocky outcrop sites in Brazil to investigate (1) the relative influence of climate on the phylogenetic diversity and structure of OCBILs; (2) their phylogenetic signature; (3) whether vegetation type influences phylogenetic diversity and structure of OCBILs after controlling for climate; and (4) the OCBILs' evolutionary median community age. We found that rocky outcrops exhibit lower than expected phylogenetic diversity and are home to plant communities composed of closely related species (i.e. phylogenetic clustering) relative to the reference species pool, primarily due to temperature seasonality. Each rocky outcrop shows a distinct phylogenetic signature, indicated by plant families with more descendant species than expected by chance. Even after controlling for climate, phylogenetic diversity and structure remain low and clustered in most rocky outcrops. The median community age estimated at the species level is lower in campos de altitude than in other rocky outcrops. Synthesis. We show that the influence of climate seasonality is pervasive in the phylogenetic diversity and structure of Brazilian rocky outcrops at different taxonomic levels. We also show that the phylogenetic signature of rocky outcrops comprises a mix of relatively old and young overrepresented plant families whose descendants contribute to their low phylogenetic diversity and phylogenetic clustering. Overall, the combination of low phylogenetic diversity, phylogenetic clustering and comparably low median community age across Brazilian rocky outcrops indicates that, on average, these OCBILs are subjected to strong environmental constraints and serve as arenas of recent diversification rather than a steady accumulation of taxa. Therefore, these findings indicate different OCBILs as hotspots for various plant lineages and species.