After the Invasion: Spread

Posted by Delayn Fritz @WildOptic

My previous blog post focused on global trade and the invasion process as a whole, but what happens to an exotic species after it becomes established? Post-establishment spread and dispersal is the next step for an exotic species transforming into an invasive species. Of particular interest are the causes of that spread, both natural and non-natural.

The simplest way that a species spreads is through its competitive edge. A study of the competitive nature of the Argentine ant (Linepithema humile) showed that they completely overcame native ants in North America in terms of resource gathering. Being able to displace native species allows the exotic invading species to take over their turf and spread locally. In fact displacing or removing native species may even lead to an ecological meltdown which can cause other invasive species to establish and cause a positive feedback loop.

ArgAntAn Argentine ant (Linepithema humile) specimen. Photo Credit: April Nobile / © / CC BY-SA 3.0

Another way for an exotic species to spread is environmental shift. This can be through habitat fragmentation and disturbance wherein a gap in the normal functioning of an environment displaces the native competitors to a point where the exotic species become dominant. One form of this that has been documented repeatedly is the increased proportion of exotic plants along roadsides, which act as a corridor for exotic species. Climate change may play another role in spread, as one study showed that increased rainfall had a positive effect on range expansion while drier years actually decreased the range of both Argentine ants and native ants in North America.

Long range jump dispersal patterns are also a key factor in spread, but this is often achieved by non-natural means. This jump dispersal usually occurs by the exotic species hitching a ride on internal trade routes or just regular vehicles. This leads to species achieving spread rates a whole order of magnitude  higher than the distance travelled by normal dispersal. It has also been shown that when this jump dispersal occurs it can actually increase the spread rate by up to three orders of magnitude.

For my MSc, I will be trying to analyse some of the data on currently established exotic ant species in New Zealand, and using taxonomic collections and their historic data to try and figure out the spread rates of different species and see if this is related to any of the aforementioned spread processes.


delaynDelayn Fritz is an MSc student in the Centre of Biodiversity  and Biosecurity, School of Biological Sciences, University of Auckland. He is interested in the invasion process of ants (Hymenoptera: Formicidae) in New Zealand. He is supervised by Darren Ward and Eckehard Brockerhoff (Scion, B3).

What is biosecurity and why should we care?

Post by Anna Frances Probert @AFProbert

Human movement and global trade are ever-increasing. Last year 5.6 million people arrived into New Zealand and more than 1.7 million containers moved through New Zealand ports. This increases the risk of unwanted organisms (disease and pest species) arriving and establishing. The management of these risks (both pre border and post border) is what biosecurity encompasses.

Unwanted organisms can have dramatic impacts on our livelihoods – impacting economic, social and environmental values. In most circumstances, introduced species (that is, species that are not native to New Zealand) are benign. Many of them won’t survive to establish, having evolved to thrive in different environments. However, a small subset do survive, establish and then spread across the landscape, becoming ‘invasive species’. If we perceive these to have a negative impact, then they are considered ‘pest species’.

Preventing new organisms from entering New Zealand is much easier and more cost-effective than trying to eradicate or control them once they slip past the border. Although there have been several successful eradication programmes conducted in New Zealand – for instance the Argentine ant on Tiritiri Matangi and the Queensland fruit fly in Auckland.

Recently, government funding for the Predator Free New Zealand project was announced, which aims to support the large-scale eradication of rats, possums and mustelids from New Zealand. This ambitious project will have massive benefits for native flora and fauna as well as remove the costs associated with the long term management of these pests.

The announcement of this project coincided with the launch of the government’s Biosecurity 2025 strategy, which aims to review and future-proof New Zealand’s biosecurity system. The current Biosecurity 2025 document outlines proposals for what might be in the direction statement, which will guide New Zealand’s biosecurity system into the future. As a nominated ‘Biosecurity Champion’, myself along with Rudd Kleinpaste, Bruce Wills and Graeme Marshall are involved in promoting the importance of biosecurity and public involvement in the consultation process.


Biosecurity Champion on the radio

Public submissions are now open, and as part of the consultation process public meetings and hui are to be held around the country.

Biosecurity is an issue that affects every New Zealander. I encourage everyone to make a submission, so that we can work together to protect our country from unwanted organisms, now and into the future.


At the Biosecurity 2025 launch

MeblogAnna Probert is a PhD student in the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland. She is using ants as a model to assess the risk posed by exotic invertebrates to native ecosystems. She is supervised by Margaret Stanley, Jacqueline Beggs, and Darren Ward.

How much water does a kauri tree use?

Posted by Cate Macinnis-Ng @LoraxCate

Ever wondered how much water a kauri tree uses? Find out in my video for the 180 Seconds of Science competition. A vote for my entry will help me win funds towards my research.

#180science is a joint competition run by the Australian Academy of Science EMCR Forum and the Royal Society of New Zealand Early Career Researcher Forum. These organisations represent emerging researchers in their respective countries. Voting closes on 22nd August at the conclusion of National Science Week in Australia so get in quick!

kauri sapflow


Dr Cate Macinnis-Ng is a Senior Lecturer and Rutherford Discovery Fellow, School of Biological Sciences, University of Auckland.  She is a plant ecophysiologist and ecohydrologist working on plant-climate interactions.



A Trip to Switzerland to learn some Wood Anatomy Skills

Posted by Julia Kaplick @julekap

In June this year I was lucky enough to escape the Auckland winter weather and learn some new skills at a Wood Anatomy Course in the Swiss Alps. It is a long running course organized by Dr Holger Gärtner, Prof Fritz Schweingruber from the Swiss Federal Institute of Forest, Snow and Landscape Research and Dr Alan Crivellaro from the University of Padua in Italy. The two main aspects of the course are the theoretical basics of the anatomical features of wood and the practical skills needed for sampling and preparing wood thin sections. This might not be obvious to everyone, but I was super excited to go and it was not because it took place in Klosters, where Prince Charles goes on skiing holidays.


Left: Microscopy with a view of the Swiss Alps. Right: Gentian, the Swiss national flower. Right: Out in the field with Prof Fritz Schweingruber, one of the world’s leading experts in wood anatomy

There are many different scientific applications for wood anatomy, but I am most interested in the connection with tree water relations. Anatomical features like lumen area and cell wall thickness vary seasonally and are strongly influenced by climatic conditions. The wood anatomy also affects hydraulic characteristics of trees. Tree species with larger lumen areas can transport more water, but they are also more likely to suffer from embolism (the formation of air bubbles) during times of drought stress.


Sample preparation – Top: With a microtome wood samples can be cut into thin section. Bottom: Staining of the sample and baking to create permanent slides


Thin section of a kauri root – Staining of the wood thin sections makes anatomical structures more visible. Left: unstained. Right: same sample stained with Safranin and Astrablue.

The first day of the week-long course was all about the theoretical background. We spent the day looking at many thin sections under the microscope, starting with simple conifers, and later learned about the more complex structures of angiosperms and even had a glimpse at some crazy looking non-woody species. On the following days we went to some beautiful alpine valleys to try out different sampling techniques and learned how to prepare and stain professional thin sections from our own samples.


Radial thin sections of rewarewa (left), tanekaha (middle) and nikau (right).

I could have easily spent the whole week cutting and staining my samples, but we also got to go on two little trips. The first one was a walk through a sustainably managed forest area, together with the responsible forester. The second trip was a visit to the Institute of Snow and Avalanche Research in Davos where we got to see the latest fashion accessories on the Swiss skiing field and also got to know a little more about how effective forest is as a protection against avalanches. Another highlight of the week was Helga, the lovely hotel cook who insisted on providing us with two hot meals a day, to keep our brains running. Yes, there was a lot of cheese and chocolate.


Left: Fancy new avalanche protection. Middle: View of Klosters from above. Right: Happiness after a long day of learning



Julia Kaplick is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. She is researching the response of native trees to seasonal variation in climatic conditions using measurements of sap flow, water relations and carbon allocation. Julia is supervised by Cate Macinnis-Ng (University of Auckland) and Mike Clearwater (Waikato University). Julia is supported by funding from the Marsden Fund.