Diversification of Neotropical birds is not directly linked to the Andean uplift, the major landscape change of the Neogene period; instead, most diversification is post-Neogene and species diversity is dependent on how long lineages have persisted in the landscape and how easily they disperse. The idea that landscape change drives diversification is firmly embedded in the biogeographical literature. It has been difficult to test this against alternative possibilities, including a model in which diversification is driven by evolutionary persistence and geographic structuring of populations by the ability of an organism to navigate the landscape matrix. Robb Brumfield and colleagues have examined patterns of genetic differentiation in co-distributed bird species in tropical Central and South America and find unequivocal support for the latter model. The data are a poor fit to the model invoking landscape change, revealing no direct link to Andes uplift. Rather, diversification times differ from each other widely and depend on how long lineages persist in the landscape and how easily they disperse. Since the recognition that allopatric speciation can be induced by large-scale reconfigurations of the landscape that isolate formerly continuous populations, such as the separation of continents by plate tectonics, the uplift of mountains or the formation of large rivers, landscape change has been viewed as a primary driver of biological diversification. This process is referred to in biogeography as vicariance1. In the most species-rich region of the world, the Neotropics, the sundering of populations associated with the Andean uplift is ascribed this principal role in speciation2,3,4,5. An alternative model posits that rather than being directly linked to landscape change, allopatric speciation is initiated to a greater extent by dispersal events, with the principal drivers of speciation being organism-specific abilities to persist and disperse in the landscape6,7. Landscape change is not a necessity for speciation in this model8. Here we show that spatial and temporal patterns of genetic differentiation in Neotropical birds are highly discordant across lineages and are not reconcilable with a model linking speciation solely to landscape change. Instead, the strongest predictors of speciation are the amount of time a lineage has persisted in the landscape and the ability of birds to move through the landscape matrix. These results, augmented by the observation that most species-level diversity originated after episodes of major Andean uplift in the Neogene period, suggest that dispersal and differentiation on a matrix previously shaped by large-scale landscape events was a major driver of avian speciation in lowland Neotropical rainforests.

The drivers of tropical speciation