Introduction Fundamental questions at the interface of biogeography and community ecology are how the evolution and biogeographic history of clades contribute to the assembly of regional biotas, and how these processes feedback with local mechanisms to shape the structure and diversity of natural communities. In the Neotropics, the uplift of the Andes has had an enormous influence on the distribution of both environmental conditions and biodiversity. Indeed, the Tropical Andes represent one of the most species-rich regions in the planet, hosting a disproportionate amount of biological diversity. How the uplift of the Andes (or any other mountain chain) has contributed to the formation of regional and local assemblages remains a topic of intense research.

Objectives In this study, we evaluated how the uplift of the Central Andes shaped the assembly of some of the most diverse regional floras in the World. Specifically, we studied patterns in the distribution of species and clades across elevations and biogeographic regions to test two non-mutually exclusive hypotheses: 1. The formation of new environments by mountain uplift promoted adaptive diversification and the colonization of the Andes from environmentally dissimilar regions; and 2. Mountain uplift primarily encouraged the immigration of clades of species that were pre-adapted to new environments at higher elevations.

Methods We combined data on the distribution of plant species at two contrasting spatial scales. We used data from the Madidi Project to characterize change in woody plant communities along elevational gradients, while we characterized large-scale plant assemblages across biogeographic regions using data from the Botanical Inventory and Ecology Network. We then evaluated the phylogenetic structure of species assemblages and the evolutionary relationships among constituent species to test predictions made by our two hypotheses.

Results Across the Neotropics, we found that most of species in the Central Andes are derived from clades of other temperate regions. Along the elevational gradient, we found that species turnover is primarily the result of high turnover of clades with pre-Andean origins. These results support the idea that the environments created during the uplift of the Central Andes were mainly colonized by clades of pre-adapted species.

Conclusions While recent research has highlighted high levels of dispersal among biogeographic regions in the Neotropics, our results suggest that it is generally easier ‘to move than to evolve’, highlight the importance that niche conservatism has in shaping modern patterns of assembly at regional and local scales. Introduction Fundamental questions at the interface