Scientists have used ancient DNA from bones of giant extinct New Zealand birds to show that significant climate and environmental changes did not have a large impact on their populations.
Two New Zealand moa and Giant Haast’s eagle (John Megahan / PLoS Biology)
Their research, published in the journal Quaternary Science Reviews, reveals that the population size of the giant moa remained stable over the past 40,000 years until the arrival of humans in New Zealand around 1280 CE.
The giant birds – measuring up to 2.5 meters high and weighing 250 kilograms – were the largest herbivores in New Zealand’s pre-human environment but were quickly exterminated after the arrival of Polynesian settlers.
“Until now it has been difficult to determine how megafauna responded to environmental change over the past 50,000 years, because human arrival and climate change occurred simultaneously in many parts of the world,” said Dr Nic Rawlence, lead author of the study and a postdoctoral research fellow from the Australian Centre for Ancient DNA and the University of Waikato.
“Using ancient DNA, radiocarbon dating and stable dietary isotope analysis, we have been able to show that before humans arrived, moa mitigated the effects of climate change by tracking their preferred habitat as it expanded, contracted and shifted during warming and cooling events,” Dr Rawlence said.
“Moa were not in serious decline before humans arrived, as has been previously suggested, but had relatively stable population sizes. The overwhelming evidence suggests that the extinction of moa occurred due to overhunting and habitat destruction, at a time of relative climatic stability.”
“The results show that range shifts and minor population fluctuations observable in the fossil and genetic record are a natural response to environmental change and do not necessarily lead to extinction,” said co-author Dr Jamie Wood of Landcare Research.
“Climate change has been blamed for megafaunal extinctions in other parts of the world, but this is not the case for moa,” added co-author Dr Jessica Metcalf of the University of Colorado.
“The very recent extinctions in New Zealand provide a unique opportunity to examine the extinction of Ice Age megafauna and the relative roles of human hunting and climate change,” said Prof Alan Cooper of the University of Adelaide’s Australian Centre for Ancient DNA.
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Bibliographic information: Rawlence et al. 2012. The effect of climate and environmental change on the megafaunal moa of New Zealand in the absence of humans. Quaternary Science Reviews, available online 2 August 2012; doi: 10.1016/j.quascirev.2012.07.004
