Human settlement of the Pacific islands triggered a wave of faunal extinctions that occurred so rapidly that their dynamics are difficult to reconstruct in space and time. These extinctions included a large wingless bird called the moa, endemic to New Zealand. In a new study, New Zealand scientists say University of Adelaide and others have reconstructed the distribution and extinction dynamics of six moa species across New Zealand. They find that the final populations of all moa species generally occur in the cold, mountainous areas that are the last remaining and least affected by humans. They also find that the final moa population refugia continue to function as isolated sanctuaries for New Zealand's flightless birds.
This is an artist's impression of the Upland Mower. Megarapteryx didinusby George Edward Lodge, 1907.
“Our study overcame previous logistical challenges, allowing us to track the population dynamics of six moa species at a resolution previously thought impossible,” said Dr Damian Fordham, from the University of Adelaide.
“We achieved this by combining advanced computational modelling with the vast fossil record, palaeoclimatic information and innovative reconstructions of human settlement and expansion across New Zealand.”
“Our study shows that despite significant differences in the ecology, demographics and timing of extinction of moa species, their distributions collapsed and converged to the same regions in the North and South Islands of New Zealand.”
Dr Fordham and his colleagues found that the last populations of any moa species lived in the same isolated, cold mountain regions that currently house many of the last populations of New Zealand's most endangered flightless birds, including Mount Aspiring in the South Island and the Ruahine Ranges in the North Island.
Hearst's Eagle (Hieraethus Moulay) attacking two moas. Image by John Megahan/PLoS Biology, doi:10.1371/journalplo.0030020.
“Moa populations were likely first to disappear from the highest quality lowland habitats favoured by Polynesian settlers, and the rate of population decline decreased with increasing elevation and distance moved inland,” said Dr Sean Tomlinson, also from the University of Adelaide.
“By identifying the last remaining populations of moa and comparing them with the distribution of flightless birds in New Zealand, we found that these last refuges also protect many of the surviving populations of takahe, weka and great spotted kiwi today.”
“Furthermore, these ancient refugia for the moa overlap with the last mainland populations of the critically endangered kakapo.”
“Although the drivers of the recent declines of New Zealand's endemic flightless birds are different to those that caused the ancient moa extinction, this study shows that their spatial dynamics are similar.”
Moas fed on trees and shrubs in the forest understory. Image by Heinrich Harder.
“The main commonality between past and present refuges is not that they are the best habitats for flightless birds, but that they remain the last refuges, the least affected by humans,” said Dr Jamie Wood, also from the University of Adelaide.
“As with previous waves of Polynesian expansion, European habitat conversion across New Zealand, and the spread of the animals they introduced, was directional, moving from the lowlands towards the colder, less hospitable mountain regions.”
Team result Published in a journal Natural Ecology and Evolution.
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S. Tomlinson othersThe ecological dynamics of the moa extinction revealed a convergent refugium where flightless birds live today. Nat Ecol EvolPublished online July 24, 2024, doi: 10.1038/s41559-024-02449-x
Source: www.sci.news
