It was the year 2002 and I was sitting in the shiny new office of our Biogeography Professor for my oral Diploma exam. It was going well, when I was asked to name an example of a Gondwanan distribution pattern, or in other words a species or group of species whose present-day distribution goes back to the ancient Gondwanan supercontinent that joined southern hemisphere landmasses during the age of the dinosaurs. Without hesitation, I named the southern beeches, the charismatic group of species that dominates most of what is left of New Zealand’s forests today. Surely, if anything was a Gondwanan relic in remote places like New Zealand, it would have to be those supposedly poorly dispersing trees. The Professor agreed, giving me full points for this answer.
Ironically, I spent the following two years putting together a molecular dataset that showed quite unambiguously that the top score for this answer was unjustified.
Like many people fascinated by New Zealand nature I had grown up in the belief that New Zealand was an archipelago lost in time, a group of islands that was the final refuge for a truly ancient fauna and flora. In my mind, it was almost like those lost places in movies in which dinosaurs still thrive and seemingly “ancient” species like the Kauri and the Tuatara fitted right into this picture. In the early 1990s, the botanist David Bellamy called New Zealand a Moa’s ark.
But bit by bit, this picture started falling apart. By the early 2000s, an ever-increasing amount of molecular and fossil evidence pointed to strong faunal and floral connections between New Zealand and other southern hemisphere landmasses long past the isolation of New Zealand from the Gondwanan super continent. Our 2005 paper on southern beeches indicated that even the poster children for ancient New Zealand biota, New Zealand’s five Nothofagus (southern beech) species, are likely descendants of Australian immigrants that arrived long after the break-up of Gondwana.
With the increasing availability of molecular data and the implementation of molecular dating strategies, evidence for species that did NOT disperse to New Zealand across open oceans became so thin on the ground that some researchers hypothesised the significant submergence of the New Zealand landmass in the Oligocene about 20 million years ago – the so-called ‘Oligocene drowning’ – might have been complete, meaning that absolutely no terrestrial Gondwana relicts could have survived in New Zealand. In 2005 the palaeobotanist Dr Matt McGlone pointed out that rather than a moa’s ark, New Zealand was more like the “fly-paper of the Pacific”.
Recently our team investigated the relationships of Australian and New Zealand bird species and found very close relationships especially for open habitat and wetland species. While for highly mobile animals like birds, these results may not be surprising, the speed with which Australian bird species seem to be able to respond to ecological niches becoming available in New Zealand is rather astounding.
Initially, we found evidence that a whole raft of Australian open habitat and wetland birds arrived in New Zealand about 2.5 million years ago, soon after the onset of ice age climates reduced the forest cover on New Zealand. At the same time, 2.5 million years is still long ago in human terms and therefore a bit abstract. However, the very same process is happening again, right now, right in front of our eyes. And this time, Australian birds are responding to human-made environmental change.
Forest cover had increased significantly in New Zealand in the last 13,000 years since the end of the last ice age, closing the door on Australian open habitat and wetland species. But extensive deforestation after human arrival about 800 years ago opened the open habitat door again, and-quite handily for newly arriving species– also wiped out some of the last badge of Australian species that had established in New Zealand 2.5 million years ago.
Species like Haast’s eagle, and Eyles’ harrier disappeared completely, the takahē and kakī/black stilt are only holding on in tiny, highly managed populations. Their places are taken by their sister species that remained in Australia 2.5 million years ago, like the pukeko and the pied stilt, or by species that are ecologically similar, like the swamp harrier. All these species and quite a few more (at least 16 in total) arrived in the last 600 years.
The conclusions we have to draw from this pattern are quite profound. Not only is New Zealand not a moa’s ark, but at least its avifauna is so well connected to other southern hemisphere landmasses that newly available niches can be filled almost “at moment’s notice” by species from across the ditch. And, rather disconcertingly, with deforestation and expansion of open habitats we have been facilitating and continue to actively facilitate the great Australification of the New Zealand bird fauna. That’s a worry, mate!