Paleoenvironments shaped the exchange of terrestrial vertebrates across Wallace’s Line

Abstract

Faunal turnover in Indo-Australia across Wallace’s Line is one of the most recognizable patterns in biogeography and has catalyzed debate about the role of evolutionary and geoclimatic history in biotic interchanges. Here, analysis of more than 20,000 vertebrate species with a model of geoclimate and biological diversification shows that broad precipitation tolerance and dispersal ability were key for exchange across the deep-time precipitation gradient spanning the region. Sundanian (Southeast Asian) lineages evolved in a climate similar to the humid “stepping stones” of Wallacea, facilitating colonization of the Sahulian (Australian) continental shelf. By contrast, Sahulian lineages predominantly evolved in drier conditions, hampering establishment in Sunda and shaping faunal distinctiveness. We demonstrate how the history of adaptation to past environmental conditions shapes asymmetrical colonization and global biogeographic structure.

Editor’s summary

The movement of species across newly connected continents millions of years ago still shapes flora and fauna today. Skeels et al . showed that species’ dispersal ability, climate tolerances, and the climate in which they evolved help to explain why biotic exchanges are typically unequal, with more species spreading from one continent than the other. Using a model simulating species ranges and diversification paired with paleoenvironmental reconstructions, the authors found that precipitation tolerance influenced vertebrate species movements across Wallace’s Line, which separates the distinct biota of Australia and New Guinea from that of Southeast Asia. Species that evolved in dry Australia were less able to cross to Asia, whereas the swath of tropical forest across the region allowed more species to move in the other direction through New Guinea. —BEL

Abstract

Environmental adaptation and dispersal ability explain which vertebrate species spread between newly connected continents.