Climate Niches of New Zealand’s Extinct and Extant Plant Genera

Throughout Earth’s history changes in environmental conditions have caused plant species to either adapt or become extinct, however, the drivers of past plant extinctions are poorly understood. This project investigates Cenozoic (66 MYA–present) plant extinctions in New Zealand to understand the impact of climate change on the fate of plants. The climate niches of extant and locally extinct New Zealand plant genera in Australia and New Zealand are analysed to determine the role that climate (temperature, precipitation, seasonality) may have played in the disappearance of many genera during Cenozoic climate changes. Species distribution data for extinct and extant genera from nine plant families and gridded climate data for Australia and New Zealand were used to determine the current climate niche of each genus. Current Australian climate contains analogues for both current and past New Zealand climate conditions. Most of the investigated New Zealand extinct genera (69%) occupy significantly different niches in Australia compared to a closely related extant genus that remain in New Zealand. The specific climate features that differentiate extant and extinct genera are not consistent throughout pairs, with precipitation and seasonality variables causing larger differences between genera than mean annual temperature. This suggests that changes in precipitation and seasonality of both temperature and precipitation are more likely to contribute to the extinction of plant species than changes in mean annual temperature. This study found no relationship between extinction age and the level of climate niche overlap between the New Zealand extinct and closely related New Zealand extant genera in Australian climate space. Niche differences were also explored between the Australian and New Zealand distributions of New Zealand extant genera to determine if niche divergence has occurred, which would suggest some level of adaptation to the cool New Zealand climate that developed in the late Cenozoic. All genera currently extant in New Zealand show large differences between their Australian and New Zealand climate niches. For most genera (73%) this difference is not significant, suggesting niche shift but not complete niche divergence. Overall, understanding the differences in the climate niches occupied by extinct and extant plant genera provides insight into potential climate drivers of historic extinctions as well as the level of adaptation to New Zealand climates of those genera that survived