Evolutionary Biogeography of New Zealand

Ever since the first western scientists visited Aotearoa New Zealand, biologists have been fascinated by the relationships of New Zealand’s biota to that of the rest of the world. (Aotearoa is the usual Māori name for New Zealand; increasingly, the combination Aotearoa New Zealand is also used to refer to the country.) The presence of notable vertebrates (e.g., tuatara), together with a high level of endemism among plants and invertebrates, was clearly a consequence of the islands’ long geological isolation. However, some elements showed clear affinities with taxa elsewhere—Australia and South America, most prominently. Explaining the evolutionary history of this biodiversity was (and is) an attractive driver for much scientific research. Leading vicariance biogeographer Gareth Nelson even claimed that, from a biogeographic standpoint, New Zealand’s biota was the most important in the world: “Explain New Zealand and the world falls into place around it.” Biologist Jared Diamond described New Zealand’s biodiversity as “the nearest approach to life on another planet.” Part of the reason for New Zealand providing so many biogeographic puzzles and exemplars lies in its active geology, a consequence of its position across the boundary of the Australian and Pacific tectonic plates. Unlike most oceanic islands, New Zealand comprises continental crust, remnants of the now largely submerged continent of Zealandia, which extended beyond present-day New Caledonia to the north, Campbell Island to the south, and Chatham Island to the east. In addition, New Zealand has periodically been subject to marine transgressions of varying degree. This geological history has been conducive to in situ geographical speciation, which has made a major contribution to the current levels of biodiversity, with some groups (e.g., punctid landsnails) remarkably speciose. In addition, the fluctuations in sea level have resulted in an excellent marine fossil record (especially in the Cenozoic era). Quaternary ice ages rapidly changed the New Zealand landscape, repeatedly isolating plants and animals in glacial refugia. Finally, the late arrival of humans in Aotearoa New Zealand resulted in widespread extinctions and biological turnover events. New Zealand’s biodiversity is enhanced by its geographical and consequent climatic range. It consists of a chain of islands extending over ~2800 km, from the subtropical Kermadec Islands in the north, via the three main temperate islands (North, South and Stewart Islands) to a number of subantarctic islands (Snares, Auckland, Bounty, Antipodes and Campbell Islands) in the south, as well as the Chatham Islands in the east. The politically Australian subantarctic Macquarie Island is often also considered biogeographically neozelanic. Various debates in biogeography, most notably the disputes between the dispersalist school and the vicariance-panbiogeographers, have cited New Zealand examples and, indeed, involved New Zealand scientists. Obviously, the arguments for and against so called “Oligocene drowning”—whether or not all of proto-New Zealand was submersed ~27 million years ago (mya)—involved New Zealand scientists and examples. More generally, the resolution of this latter debate illustrated how to evaluate dispersalist and vicariance hypotheses using modern techniques and integrative approaches.