Nature's recovery will exceed the time that humans have existed

Friday, 16 August 2019

New Zealand bird diversity could take 50 million years to recover from extinctions caused by humans, a new study has found.

'The conservation decisions we make today will have repercussions for millions of years to come,' says Luis Valente​ of Museum für Naturkunde in Berlin.

'Some people believe that if you leave nature alone it will quickly recuperate, but the reality is that, at least in New Zealand, nature would need several million years to recover from human actions – and perhaps will never really recover.'

The researchers are not saying moa, Haast eagles or huia will re-emerge through evolution.

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Rather they are saying evolution will eventually produce novel bird species and it will take up to 50m years for the number of different bird species – diversity – to equal the number of bird species that lived on Zealandia prior to human arrival.

'Our study … clearly reveals that the recovery of New Zealand's diversity will not be quick and will, for example, far exceed the amount of time that humans have existed,' the scientists reported in the journal Current Biology.

'While the number of lost or threatened bird species often has been quantified, the broad-scale evolutionary consequences of human impact on island biodiversity rarely have been measured,' say the researchers, among them Juan Carlos Garcia-Ramirez of Massey University.

They used statistical tools and techniques to analyse the DNA of existing and extinct NZ birds. Among other things, they calculated the speed at which Zealandia birds diversified before human arrival, as well as their natural extinction rate. 

In addition to the 50m year figure, they also predicted it would take 4m years to recover the diversity lost since European arrival and up to 10m years to recover the diversity that is currently under threat if it actually goes extinct.

'While the impact of humans on New Zealand's extinct and threatened bird species numbers is relatively well understood, little is known about the long-term macroevolutionary​ impact of anthropogenic extinction,' the authors wrote. 'In other words, how far have humans perturbed this unique and isolated biological assembly from its natural state?'

'This is an interesting question and concept,' said  Dr Nic Rawlence, a senior lecturer in ancient DNA at the University of Otago, who was not involved in the research.

The researchers excluded migratory, vagrant, marine, and introduced birds.  

Excluding introduced birds was interesting because it could be argued that the 37 introduced species have already returned diversity to pre-human levels.

'We didn't count those species because we were interested in the natural processes,' said Garcia-R in an email.  

'Those species were brought to NZ by humans and as such, they don't have the 'equivalent value' for those processes,' he wrote. 

Excluding shore and seabirds was necessary for technical reasons but the researchers predicted their diversity would recover along 'similar' time periods.

The only other similar study to measure the evolutionary impact of humans on an island system found that 8m years have been lost in Caribbean bats.

The researchers hoped to apply their techniques and tools to other islands globally.

'As conservation funds are limited, measuring the evolutionary time under threat in multiple islands worldwide may contribute to conservation efforts by prioritising the preservation of islands that currently have the most evolutionary history under threat,' they wrote.

'Our results caution that the policy decisions we make today will have implications far into the future. Luckily, New Zealand's pioneering bird conservation efforts may yet prevent millions of years of evolutionary history from further being lost.'