The relative roles of in situ diversification and lineage dispersal underlying diversity patterns at the assemblage level

Speciation, extinction, and dispersal are the historical processes influencing the spatial distribution of lineages and strongly influence diversity patterns. Here, we apply a recently developed methodological approach to quantify the relative legacies in situ diversification history (i.e. diversification occurring in the biogeographical region) and historical dispersal (inferred from ex‐situ diversification) on current diversity patterns of the plant genus Myrcia (Myrtaceae) in assemblages distributed across the Brazilian Atlantic Forest. To distinguish among these processes, we proposed a framework that characterized the assemblages based on the mean colonization age of the assemblages, phylogenetic structure, species richness and proportion of in situ diversification. Our results suggest that environmental dynamics have played an important role in shaping diversity. In the Southern Atlantic Forest, environmentally stable areas appear to have served as cradles for cold‐adapted lineages. In the central region, environmental instability in this montane area seems to be an unstable area acting as cradle, with assemblages showing moderate to high in situ diversification and intermediate colonization ages. In the Northern Atlantic Forest, older and richer assemblages with high phylogenetic diversity suggest climatic stability and a museum role. In contrast, the Central‐West region, with younger colonization ages and a higher proportion of lineage dispersal, appears to act as an unstable sink for lineages. By combining community phylogenetics and diversification metrics, we infer evolutionary legacies at the assemblage level and disentangle the roles of in situ diversification and lineage dispersal. In some regions of Atlantic Forest lineage dispersal appears more relevant, possibly due to weaker selection pressures. In contrast, colder areas may have favored lineages with broader climatic tolerance. Our findings reveal distinct biogeographic dynamics across the Atlantic Forest, including areas acting as cradles, sinks, and refugia, and demonstrate the value of assemblage‐level diversification metrics in understanding within‐biome evolutionary processes and their influence on current diversity patterns.