14 October 2010

The long invasion

New Zealand has worried about invasion for the last 200 years. Dotted around our major harbours are gun emplacements built to repel Russian and Japanese imperial designs in the late nineteenth and mid twentieth century’s, respectively. Of course neither of these invasions eventuated but there have actually been enormous numbers of successful invasions into our proud island nation. Thousands of plants, hundreds of insects and multitudes more have colonised New Zealand since Europeans themselves arrived. Species continue to arrive and New Zealand spends a lot of time and effort in preventing them from doing this or in trying to reduce the impact of these invasive species when they do get here. Much of the ecological research at Lincoln University and the Lincoln Crown Research Institutes is centred around these issues. One strand of this research is to understand the rules that describe the spread of non-native species through the landscape and over time. Many aspects complicate our understanding of these rules especially the fact that rules may differ at the level of local habitat, region or island. Also, factors that are important in the early phases of an invasion, like human modifications of habitat that suit the invading species, may be less so after several decades when the invading species becomes more widespread.

hawkweedA carpet of Hieracium pilosella hawkweed in the Canterbury high country. Photo by Mollivan Jon
In a new study published in Austral Ecology, Nicola Day and Hannah Buckley of Lincoln University have looked at the fate of three closely related invasive species over three decades. The plant species Hieracium (Hawkweed, Asteraceae) are native to Europe but are invasive in many parts of the world where they often degrade native and pastoral grasslands. In New Zealand, three species in particular, H. lepidulum, H. pilosella, and H. praealtum, were introduced accidentally in grass-seed mixtures and cause major problems in high country areas. Day and Buckley wanted to know which ecological and environmental traits explained the spread of these species, whether these traits were important at all scales and whether they were the same for all three species. To test these ideas they were able to make use of a fantastic long term study. In the mid 1980s, 124 study sites were set up in high altitude tussock grasslands in Otago and southern Canterbury. Information about the plant species found at these sites and characteristics of the site, like levels of calcium and phosphorus and climate data, were collected. The sites were resampled in the mid 90s and again between 2005 and 2007. So Day and Buckley had the luxury of looking at the changes that had occurred over three decades.


Overall, all three species increased at all scales during the study. All three species had complex relationships with the various traits measured. However, it appeared that there were some predictable patterns to be detected. For example, all three species were better able to invade areas of short-tussock than tall-tussock. It also appeared that each species shared a similar invasion trajectory for their population spread but that they were at different phases in their invasions. H. praealtum is widespread but its increase is slowing and is probably towards the end of its invasive phase. H. pilosella is in an earlier stage of its invasion and continues to spread at a high rate. H. lepidulum is only a minor component in the grasslands and seems to be in the earliest lag phase of its invasion (H. lepidulum was the last of the three species to naturalise). This study shows the benefit of sampling over decades and over large distances. In some ways this is a little worrying for ecological research which typically does studies over small scales and one or two years. Day and Buckley show that to understand the small scale you sometimes have to think at the larger scale.

Darwin & the Sandwalk 3

Here is one that is just as topical as it was in the 90s. The Marsden Fund is the major fund for 'blue skies' (i.e. no immediately applied purpose) science in New Zealand. This year 91% of those that applied failed to get funding! I'm not sure that Charles would have recieved much funding in this environment! "Oh yes I'd like to breed a few pigions and see what happens".

01 October 2010

Life above our heads – the invertebrate fauna of West Coast rata canopy

This blog post was written by postgraduate student Andrea Honig as part of the course, Research Methods in Ecology (Ecol608).

Kathrin Affeld did not choose an ordinary topic for her PhD thesis at Lincoln University. She and her team of scientists carried out a research project on the invertebrate fauna high up in the canopy of northern rata trees on the West Coast of the South Island of New Zealand. Northern rata, or Metrosideros robusta, in the family Myrtaceae, are tall emergent trees in New Zealand's temperate rain forests and before Kathrin's work their canopies were unchartered territory for science. Her project would be a real pleasure for all the outdoor climbing fans among us.

To collect data, Kathrin climbed 15–25 m up each tree before she could set up her experiments. Photo by Mollivan Jon

As Kathrin stated in 2004, “I’m looking at invertebrate communities that live in epiphytes and their response to climate change.” The study gave a significant insight into the high level of invertebrate diversity present in the canopy of northern rata trees at the two sites studied and uncovered several species new to science including one genus of species


Kathrin and her colleagues decided to sample epiphyte mats directly, because conventional methods, such as insecticide fogging, would not be appropriate for capturing all invertebrates, as any individuals in funnel shaped plants or thick humus layers would be missed. Each sample had to be detached from the bark and transported carefully in plastic bags to the lab. Invertebrates were extracted using Berlese funnels over several days.

Berlese funnels are a common method to extract invertebrates from soil or litter samples. Heat produced by a light bulb dries the sample. Invertebrates will move away from the light and heat and fall down the funnel through a mesh into a preservative fluid (for example, ethanol).

Berlese funnel.
Illustration by
Andrea Höing, Lincoln University.

To make sure all invertebrates were extracted the researchers washed all remaining organic material over three stacked sieves with their mesh size decreasing from 1.7 mm to 75 μm.

Berlese funnels in action extracting invertebrates from Kathrin Affeld's canopy samples. Photo by Mollivan Jon

Identification could be conducted by expert taxonomists for most species to family level, but it was a great challenge to go further and just 16.2% were assigned to species level. There were at least 10 new species found and one new genus, although there is likely to be many more species new to science amongst the many specimens that could not be identified to species. All of the species collected in this study can be viewed at the Entomology Museum at Lincoln University, Canterbury, New Zealand.

Data analysis showed that the study reflected only a portion of the real biodiversity in the podocarp-broadleaf forests canopy. This portion already indicated a highly diverse invertebrate fauna, both functionally and taxonomically (more than 242,000 invertebrates were collected). Results were presented in a 17 page long table giving important baseline information to each species, site where they were found, sampling time, feeding guild and their status, if they are endemic, introduced, cosmopolitan or native.

The most interesting discoveries included the following.
  • Several undescribed and new species in epiphyte mat habitats (>10 new species).

  • Extended geographical ranges for various species.

  • Large arboreal ant colonies; until this study they had been known as solely ground nesting species.

  • Relatively small numbers of exotic insect species (7 species, all in relatively small numbers); this information is very important for assessing invasion risk.

All this information is important in terms of national biodiversity inventories and global species estimates. Kathrin further recapitulated the importance of investigating invertebrates and epiphytes of New Zealand: “Understanding their distributions and interactions is fundamental for predicting and dealing with the threats posed by habitat loss and climate change. Data from my study could further be incorporated in climate change models and used to identify conservation priorities.”

This study was the first invertebrate inventory of New Zealand forest epiphyte habitats. It provides important baseline data for conservation of biodiversity in New Zealand's forests. However, it also highlights how much we have yet to learn about the amazing bio-diverse canopies above our heads. For detailed information on this study see Affeld et al. 2009.

Affeld, K., Worner, S., Didham, R.K., Sullivan, J. Henderson, R., Malumbres Olarte, J., Thorpe, S, Clunie, L, Early, J, Emberson, R., Johns, P., Dugdale, J., Mound, L., Smithers, C, Pollard, S., and Ward, J. 2009. The invertebrate fauna of epiphyte mats in the canopy of northern rata (Myrtaceae: Metrosideros robusta A. Cunn.) on the West Coast of the South Island, New Zealand. New Zealand Journal of Zoology 36,177–202.