Our Changing World

Thursday 3 December 2015, with Alison Ballance & Veronika Meduna

On This Programme

Ecology in action

It’s conference time of year for scientific societies, and around the country researchers are practising their power point presentations and public speaking. I heard many interesting things at the recent New Zealand Ecological Society conference in Christchurch, which involved over 300 people and lasted for 3 days.

Two things stood out strongly for me: some sometimes disturbing long term trends in our native flora and fauna, and new takes on old rodents. We’ll get to the rats and mice later, but first – there has been some fascinating work analysing long term data sets. Interestingly some of this data has been collected almost accidentally, by students on an annual ecology field trip in one case and a single scientist in another.

Falling bird numbers

In a large Citizen Science effort, members of the Ornithological Society of New Zealand – now known as Birds NZ - collected bird records in the 1970s and again in the early 2000s, for two Atlases of Bird Distribution. Susan Walker at Landcare Research has been looking at what changed in the 25 years between the two surveys, and what she’s found has her worried.

She says that in the 1970s native birds had already disappeared from settled and productive landscapes but were still present in large numbers in native forests. Twenty five years later it’s a different story.

“What we’ve seen since the 1970s is a real emptying out of those forests. And the most striking pattern is that it’s not just any birds – it’s New Zealand’s deep endemic birds, those that are found nowhere else in the world and are in higher taxonomic levels such as orders and families. They are the biodiversity that New Zealand adds to the world.”

Kiwi, whio or blue duck, kokako and rifleman are just some of the birds that suffered significant population declines over the 25 years, and she says predators are almost certainly to blame as there has not been any significant land use change.

The other striking decline that she has found is in the wading birds, gulls and terns, in particular the endemic species that breed almost exclusively in inland South Island. She mentions dotterels, black-fronted terns and black-billed gulls in particular.

“They’re not only being hit by predators, they’re also being hit by massive scale land use change.”

 These inland areas are being rapidly developed for intensive farming, and she says this makes these species of particular conservation concern as there is nowhere else for these species to move – it is not possible to relocate them to islands.

“Forests are just recovering from their last disturbance.”

Beginning in 1980, now-retired University of Auckland botanist John Ogden began taking stage 2 and 3 students to the Kaueranga Valley in the Coromandel, to teach them how to identify native plants and carry out basic vegetation monitoring.  Now I know this because I’ve been one of those students! These autumn field trips have been an annual event for 35 years, and Bruce Burns and George Perry have now taken all that data and analysed how the forest has been changing. It helps to know the longer term changes that have taken place in the forest. Early Maori burnt some of the forest, and in the late 19th and early 20th century there was widespread kauri logging. Then possums arrived in the area in the 1960s, with numbers peaking around 1980.

In the 1980s there was quite a lot of kanuka and kohekohe present. Kanuka is an early successional species, and as the forest has matured it has begun to disappear, to be replaced by slower-growing climax species. But the kohekohe has also almost disappeared, and the researchers think this is due to possums, which seem to have also had a significant impact on mamaku, or black tree ferns. Kauri doesn’t seem to be regenerating, and this is puzzling the researchers.

Bruce says these are the kind of changes that always happen in forests, but are often invisible to us because of the long time frames they happen over.

“There’s a huge value in having these measurements that we return to over a long period of time.”

Forty five years of moths

Like all good field biologists, moth and butterfly expert Brian Patrick keeps detailed notebooks.  Jon Sullivan at Lincoln University is involved in digitising and analysing these records, which cover 45 years, making it the longest monitoring dataset for invertebrates in New Zealand. Jon says that Brian has kept notebooks from the time of his childhood in Invercargill.

“There is no other dataset like it in New Zealand – and this is information that nobody knows.”

Jon says that overseas, where there have been people recording these kinds of things for long periods of time, there have been noticeable declines in butterfly numbers, and Brian is reporting the same thing here.

“When Brian goes out light trapping at night and records all the moths that come into the light he doesn’t see large numbers of moths like he used to.”

Jon says the analysis so far shows declines in moths in urban areas, with moths in agricultural areas either just holding their own or going down in number. On the other hand, moth numbers in remote untouched areas seem to be going up.

“All this evidence is pointing to some pretty alarming changes in our moth fauna, but until now we just haven’t had the numbers to back that up.”

Small rats eating big birds

Ancient DNA is increasingly allowing us to look back hundreds and even thousands of years to find out what species were around and what their lifestyles were. Jamie Wood from Landcare Research has previously found information about the diet of now extinct moa from their coprolites, or dried droppings, and he’s now finding even more intriguing diet information from kiore coprolites, kiore or Pacific rats of course being the first of 3 rat species to colonise New Zealand, having arrived with early Maori.

A preliminary look at a dozen rat coprolites has shown evidence of parakeet feathers, beetles and various plant material. But DNA analysis revealed something startling in one coprolite: moa DNA. The heavy-footed moa, which was a short but heavy moa, was abundant in the area that the kiore coprolites were found, with many birds nesting there, and Jamie says they are reasonably certain it shows that kiore were eating either adult birds or chicks. He says it’s difficult to discount that kiore might have been scavenging dead moa, but there is very little evidence that kiore are scavengers.

He says the idea that a small rodent like kiore might have even eaten much larger birds such as moa, and contributed to their rapid extinction after Maori arrived in New Zealand less than 800 years ago, was first suggested by the late Charles Fleming. Charles knew of evidence from several Pacific islands where kiore had killed and eaten seabirds as large as albatross, in some cases causing an annual decline of 2% in seabird numbers. This fits with recent evidence of mice on Gough and Marion islands killing and eating large numbers of seabirds.

Jamie is expecting more surprises when the DNA analyses are completed over the next few weeks.

Uunexpected mice.

Kiore or Pacific rats arrived in New Zealand with Maori, while ship rats, Norway rats and mice arrived with early Europeans. Caroline King from Waikato University has been using DNA and some historical sleuthing to find out when mice arrived here and where they came from – and she’s discovered something rather surprising.

Given New Zealand’s ties with Great Britain she expected that the mice here would all be Mus musculus domesticus, the family lineage that is common in western Europe. However, recent sampling and mitochondrial DNA analysis of mice around New Zealand shows that while the European lineage is common in northern New Zealand , a south-east Asian lineage – M.m. castaneus – was common in southern New Zealand.

Caroline says that historical shipping records showed that between 1792 and 1840 there were frequent ship movements between the Bay of Islands in the north and Sydney, which would have given mice many opportunities to reach here. She suspects, however, that the south-east Asian mice more likely arrived around 1810 with sealers working in southern New Zealand. The mice may have come directly from Canton, or via Sydney, although to date there has been no evidence of the Asian family lineage in Sydney.

The European and Asia house mice do interbreed here, although Caroline says they usually appear to have Asian mothers and European fathers, and the two subspecies can also be found living in close proximity without interbreeding.

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Protecting grape vines from leafroll virus

Karmun Chooi with grape leaves showing distinctive red colour with green veins that indicate a leafroll-3 infection.

Photo: RNZ / Alison Ballance

The New Zealand wine industry produces hundreds of millions of litres of wine each year, has an annual turnover of more than $2 billion, and is the country’s biggest horticultural export by value. Underpinning it is more than 35,000 hectares of vineyards, planted in a range of grape varieties. And helping growers keep those grape vines in good health is a job that post-doctoral researcher Karmun Chooi at Plant and Food Research is focused on.

Karmun is researching a virus called Grapevine Leafroll associated Virus 3, or leafroll 3. Leafroll disease has been a problem in New Zealand for more than a hundred years, and it affects all varieties of grape as well as rootstocks. It is spread between grape vines by mealy bugs, small insects which chew into the leaves and transmit the virus as they do so. It can also be spread by tools used in propagation.

The virus causes visual symptoms such as downward rolling of the leaf margins, and in red varieties of grapes it causes premature reddening of the leaves. Although the leaves turn red the leaf veins remain green, which distinguishes leafroll 3 from other diseases. More importantly, it affects crop yield, causing uneven ripening, and reducing sugar content and increasing the acidity of grapes.

Reddening of leaves caused by the leafroll-3 virus - the green veins are a clear mark of the virus

Grapevine leafroll-associated virus-3 - or leafroll-3 as it is more commonly known - is spread between grapevines by mealybugs or during pruning. As well as causing leaf reddening, it decreases sugar and increases acidity in grapes.

Photo: Plant and Food Research

Controlling mealy bugs and removing infected vines are the only way of controlling the virus. This can be an expensive undertaking: in a case study from the Craggy Range vineyard, published by New Zealand wine, the cost of removing eight hectares of infected premium chardonnay vines was calculated to have a total cost (including lost production potential) of $1.3 million.

Karmun says that genetic work has shown there are at least six genetic strains of the leafroll 3 virus in New Zealand, which vary in their severity. Her current study is looking at three genetic strains of the virus in merlot, pinot noir, sauvignon blanc and pinot gris. Plant and Food is carrying out field trials in three different grape-growing locations, looking at the timing and severity of symptom development in the field, and Karmun is also working in lab.

Detection is a key part of leafroll 3 management. The virus is currently identified using an antibody-based ELISA test which identifies the virus’s distinctive coat protein. Vaughan Bell at Plant and Food Research is also developing a visual key that he hopes grape growers will be able to use in the field to quickly assess the extent of virus infestation in red grape varieties; visual assessment doesn’t work in white grape varieties. Karmun is also involved in developing new molecular tools that could be used for identification in future.

Karmun is investigating an idea called ‘mild strain cross protection’. This acts a bit like vaccination for the vines, as vines infected with a mild strain of leafroll 3 develop very few symptoms and seem to be resistant to developing the more virulent varieties of virus.

“First we need to understand what strains of virus we naturally have in the vineyards, and then we can look for a milder strain,” says Karmun. “Mild strain cross protection is one method for protecting crops but much more research is required to really understand what it might be capable of.”

The top line of grape vines shows a slight reddening of leaves,while the lower line of grapes has many more deeply red leaves

Mild (top) and severe (bottom) strains of the leafroll-3 virus affecting grape vines planted in an experimental plot.

Photo: Plant and Food Research

This research is part of the Virus Elimination Project, a New Zealand Winegrowers' Research Project that is co-funded by the Ministry for Primary Industries (Sustainable Farming Fund).

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