Southern Hemisphere Biogeography Inferred by Event-Based Models: Plant versus Animal Patterns

TLDR

The Southern Hemisphere has long been viewed as a vicariant region shaped by Gondwana’s breakup, but recent molecular and paleogeographic evidence suggests dispersal may play a larger role than previously thought. The study aimed to compare vicariance and dispersal in Southern Hemisphere biotas using 54 animal and 19 plant phylogenies. The authors applied parsimony tree fitting and permutation tests to assess how well biogeographic patterns align with Gondwana’s breakup and to detect dispersal events. Animal phylogenies largely support Gondwana’s breakup with frequent trans‑Antarctic dispersal, while plant phylogenies are better explained by dispersal—especially trans‑Tasman movements—and the South American biota appears hybrid with limited exchange between its northern and southern regions.

Abstract

The Southern Hemisphere has traditionally been considered as having a fundamentally vicariant history. The common trans-Pacific disjunctions are usually explained by the sequential breakup of the supercontinent Gondwana during the last 165 million years, causing successive division of an ancestral biota. However, recent biogeographic studies, based on molecular estimates and more accurate paleogeographic reconstructions, indicate that dispersal may have been more important than traditionally assumed. We examined the relative roles played by vicariance and dispersal in shaping Southern Hemisphere biotas by analyzing a large data set of 54 animal and 19 plant phylogenies, including marsupials, ratites, and southern beeches (1,393 terminals). Parsimony-based tree fitting in conjunction with permutation tests was used to examine to what extent Southern Hemisphere biogeographic patterns fit the breakup sequence of Gondwana and to identify concordant dispersal patterns. Consistent with other studies, the animal data are congruent with the geological sequence of Gondwana breakup: (Africa(New Zealand(southern South America, Australia))). Trans-Antarctic dispersal (Australia ↔ southern South America) is also significantly more frequent than any other dispersal event in animals, which may be explained by the long period of geological contact between Australia and South America via Antarctica. In contrast, the dominant pattern in plants, (southern South America(Australia, New Zealand)), is better explained by dispersal, particularly the prevalence of trans-Tasman dispersal between New Zealand and Australia. Our results also confirm the hybrid origin of the South American biota: there has been surprisingly little biotic exchange between the northern tropical and the southern temperate regions of South America, especially for animals.