Latitudinal patterns and climatic drivers of Laurasian and Gondwanan angiosperm tree distributions in forests of the Americas

The biogeographic affinity of a lineage leaves imprint on its niche, and influences its distribution under biotic interchange between landmasses. Since the beginning of the Quaternary, North America (a remnant of Laurasia) and South America (a remnant of Gondwana) have been united, and triggered the Great American Biotic Interchange. Based on existing knowledge, we expect more Laurasian lineages to occur at higher latitudes, in colder or drier areas; and more Gondwanan lineages to reside at lower latitudes, in hotter and wetter areas of the Americas. Moreover, the tropical niche conservatism (TNC) hypothesis states that the tropical flora be most ancient. If so, then both younger Laurasian and Gondwanan lineages would occur in regions at colder and higher latitudes. Here, we examine the latitudinal patterns of species richness and mean family age of Laurasian and Gondwanan angiosperm tree lineages in 422 forest plots distributed across the Americas, and investigate the underlying continent and climatic drivers. We found opposite latitudinal and climatic patterns for species richness of Laurasian and Gondwanan lineages, the former declined towards lower latitudes and hotter climates, whereas the latter declined towards higher latitudes and colder climates. In particular, more pronounced climatic patterns for species richness of Laurasian and Gondwanan lineages were observed in North and South America, respectively. In addition, the mean family age of Laurasian lineages declined towards higher latitudes and colder climates, and for Gondwanan lineages it also decreased towards higher latitudes in South America, hence supporting the TNC hypothesis. We suggest Laurasian and Gondwanan angiosperm tree lineages in forests of the Americas exhibit diverged climate niche preferences, perhaps partly due to diversification of the former in extratropical climates in recent geological times.