Did interaction between human pressure and Little Ice Age drive biological turnover in New Zealand?

Aim: To test for simultaneous Holocene biogeographic turnover events in the New Zealand region. Specifically, we synthesize ancient DNA, radiocarbon data and archaeological data to assess the chronologies of late Holocene lineage extinction and replacement. Location: Cool-temperate coastal ecosystems of New Zealand and the subantarctic. Methods: We present new ancient DNA and radiocarbon data for New Zealand sea lions, and synthesize existing climatic, genetic and archaeological data, to test for synchronous megafaunal extinction and replacement events. The collated data include ancient DNA sequences from over 200 ancient sea lion and penguin specimens, in addition to 150 modern genetic samples. Results: Our temporal genetic analyses show that, following human-driven extinction events, synchronous marine megafaunal replacement events occurred at around 1500 AD, coinciding with the Little Ice Age onset and an associated drastic human demographic decline in southern New Zealand. Conclusions: A combination of climatic and human demographic shifts likely facilitated northward expansion of subantarctic sea lion and penguin lineages, replacing extirpated mainland New Zealand marine megafauna. Broadly, the interaction between human pressure and late Holocene climatic change may explain multiple biological turnover events in the Southern Hemisphere.