Corridors and reservoirs: An analysis of inter-Andean historical biogeography

The Andes are a global biodiversity hotspot, and the formation of this mountain range has been linked to the rapid diversification of numerous lineages across the Tree of Life. In addition to generating high species richness, the Andes may have functioned as a reservoir from which lineages dispersed across South America. Recent syntheses of Andean geological history, together with the growing number of phylogenetic studies across diverse Andean clades, provide an opportunity to integrate current knowledge of the historical biogeography of the Andean biota. Here, we present a meta-analysis of phylogenetic studies in which we scored disjunction events within and out of the Andes based on published biogeographic reconstructions. Across clades and through time, dispersal events within the Andes were approximately as frequent as those out of the Andes. The highest number of extra-Andean disjunctions originated in the northern Andes, despite this region being the most recently uplifted. Our results also indicate sustained bidirectional dispersal within the Andes over the past 50 million years, with northward dispersals occurring at a slightly but significantly higher rate than southward movements. Furthermore, crown clades of Andean plants tend to be older than those of animals, the latter largely originating within the past 30 million years. Overall, these findings demonstrate that the Andes have functioned both as a reservoir and as a corridor of biodiversity across clades with widely differing dispersal strategies.