Researchers have developed a new way to quantify the impact of human activity on other species – and they have used it to estimate that it would take 50 million years for the unique bird fauna of New Zealand (NZ) to return to pre-human levels of diversity.
“Some people believe that if you leave nature alone it will quickly recuperate, but the reality is that, at least in NZ, nature would need several million years to recover from human actions – and perhaps will never really recover,” says research leader Luis Valente, from Museum für Naturkunde in Germany.
Islands have long been ideal places for the study of the deleterious effects of anthropogenic change on biodiversity, and NZ is no exception.
The arrival of Polynesian Maori 700 years ago, and Europeans some 2-300 years ago, resulted in one the largest waves of extinction documented, and the loss of nearly half of the bird fauna.
Unlike other land masses, NZ’s vertebrate fauna is dominated not by mammals but by birds. Isolation and millions of years of evolution resulted in a unique assemblage of birds, including the now extinct Moa family. It represents a large and distinct branch on the tree of life.
Today, over 30% of the country’s surviving bird species are threatened by extinction.
In their recent study, Valente and colleagues Rampal Etienne, from the Naturlis Biodiversity Centre in the Netherlands and Juan Garcia-R, from NZ’s Massey University, set out to answer two questions: “how far have humans perturbed this unique and isolated biological assembly from its natural state?” and “how deep will the evolutionary impact be if currently threatened species go extinct?”
The NZ avifauna extinction is well documented, Valente says, due to decades of paleontological and archaeological research.
“Also, previous studies have produced dozens of DNA sequences for extinct NZ birds, which were essential to build datasets needed to apply our method”, he adds.
The researchers first compiled the first complete dataset of NZ native and resident land birds. This dataset was then used in computer analysis – a model dubbed DAISIE (dynamic assembly of islands through speciation, immigration, and extinction).
DAISIE, combined with metrics of speciation recently devised for Caribbean bats, enabled the researchers to estimate how long it would take, on average, for bird species diversity in NZ to return to a given level.
And the answer is, a very long time indeed.
The findings, published in the journal Current Biology, estimate that it would take 50 million years to return to pre-human levels of diversity – and that if today’s threatened species went extinct despite conservation efforts, it would take 10 million years to return to today’s diversity levels.
Measuring the evolutionary time that it would take to restore diversity levels in other islands worldwide may help make a case for the preservation of those islands that currently have the most evolutionary history under threat, the researchers add.