Research Reveals Precipitation Tolerance Explains Vertebrate Species Spread Between Newly Joined Continents

A new study helps explain why rates of species exchange are at least twice as high from west to east than in the opposite direction across Wallace's Line. The study included an analysis of more than 20,000 species belonging to all 227 families of terrestrial vertebrates present in the Indo-Australian archipelago. As tectonic plates merge, once disparate continents can connect and create new opportunities for biotic exchange. Species movement across newly connected continents millions of years ago continues to shape assemblages of flora and fauna today. One of the most well-known biotic interchanges followed the convergence of the Australian and Eurasian tectonic plates, which created a geologically complex archipelago composed of thousands of islands. There exists one of the most recognizable patterns in biogeography – the faunal discontinuity across what is known as Wallace's Line. Though the species distribution across this line is asymmetric, the mechanisms underlying this pattern remain poorly understood. Here, Alexander Skeels combined paleoenvironmental reconstructions of temperature, precipitation, and plate tectonics over the past 30 million years with a mechanistic model of biodiversity to better understand the dynamics underlying major biotic exchanges and the biogeographic patterns they produce. Skeels et al. discovered that precipitation tolerance and dispersal ability influenced vertebrate species' movements across Wallace's line. According to the findings, species that evolved in dry Australian regions were less able to cross into Asia (east to west exchange), while the large tracts of tropical forests across Asia and New Guinea allowed more species to move in the other direction (west to east).