Working with Nick Porch

After arriving and finding out that 1 of the modules I had chosen was full I had a lot of drama trying to select another module. It seemed like every one I wanted to do was full and had no way of squeezing me in, despite coming from the opposite side of the planet and all the modules I could do were of absolutely no relevance or interest to me. After a lot of faffing around and meetings, Deakin agreed to let me take the Research module. The reason they weren’t keen originally was because the module is run all year so that students have time to conduct their research before writing it up. It was basically like a mini dissertation, and obviously with only 4months to do it, they were sceptical. We agreed however that I would assist a staff member with their research and then do the write up as normal to save time and ensure I left Deakin with the right amount of credits.

I contacted a few staff members to see if they had room for me on their research teams and eventually I ended up speaking to Dr Nicholas Porch. He had been to an island called Raivavae in The Australs. He’d taken core samples in an attempt to map out insects in 3 time periods; Pre-human, Polynesian and European. He kindly agreed to let me sort one of his core samples, separating out the different species in each time period. With no previous experience in this area, he showed me what flies or ‘crinoids’ looked like under a microscope, and also mites and beetles. Nick had a particular interest in the beetles as this is his specialty.

I was based in the Palaeontology department and even had my own desk. I had my own microscope set up and space to store the samples I was working on. I loved the time I spent there as all of the paleo guys were beyond lovely. It did take me a while to be able to tell the different part of the beetles apart, as beetles don’t preserve in one piece but I got there in the end!

At the end of my 4months, Nick made me a graph displaying the data I had collected. The graphs clearly showed how the species richness and abundance had changed throughout the different time periods, and this also reflected the human state at the time. Showing how the insects had to adapt to the changes humans made on the island; like the construction of rice paddies and the introduction of new species due to the introduction of trade.

To complete the assessment part of the module I had to write a 1500 word scientific report [95%] and then present it [5%]. The presentation was extremely nerve racking considering that there were 5 or 6 other people speaking, and I was the only speaker not presenting their PhD! The room was filled with lecturers and other professionals, there to mark the people studying under them or just there out of interest. I was heckled a bit during the question portion of my presentation but I felt I held my own and answered adequately.

I received 97% overall and a high distinction! It was a great way to round off the end of my trip!


My Report:

Prehistoric to Modern Human Impact on the Insect Diversity of Raivavae (Austral Islands)

 

By Rebecca Dale

INTRODUCTION

The purpose of this research project was to determine whether there is a change in the species type and abundance of the insect fossils found on the island of Raivavae. We can compare this data to what we already know about prehistoric human colonisation to see if any patterns are present.

The native flora and fauna found on the Pacific islands were isolated and their evolution reflects this (Kirsch, 2003). Due to the lack of natural predators on the islands, the species present were able to take advantage of the resources available and fill numerous ecological niches.

Humans are said to have begun settlement on Raivavae around 1,000 years ago (Figure 1). With the arrival of the Polynesians came change to both the habitat and species present. This was due to ecological degradation caused by the establishment of agricultural practices and a number of foreign species that were accidentally introduced (Anderson, 2008).

 

Figure1. Map showing human colonisation of remote islands. Ka represents a thousand years 

METHODOLOGY

Sampling and sorting

The location that was used to conduct this study was the island of Raivavae, which is located in the Australs, French Polynesia. This project focuses on the analysis of a core sample that was collected by Dr Nicholas Porch (Deakin University) using a 2.7 metre corer. The core sample was separated into depth samples ranging from 0-5cm to 240-245cm. After being returned to Deakin University, Melbourne, Australia the samples went through the initial sorting process which included sieving the material, sorting it into different categories including insects, seeds and miscellaneous and storing them in ethanol. 

Identification

The insect includes beetles, mites, chironomids and moth larvae. All of these specimens tend to be well preserved, even if just in fragments making them clearly identifiable. The chironomids and the moth larvae are predominantly represented by the hypostromal structure of the head capsule. Typically mites preserve whole whereas beetles tend to be represented by a number of fragments. The most commonly seen beetle fragments include the head, thorax and elytra. All of these body fragments are useful in identification and can be used to determine the genus, and frequently the species.

The individual specimen fragments were identified using two primary sources: 

1. Porch, N. (2009) Insect Identification Guide. Raivavae, Austral Islands.

2. Dr Nicholas Porch’s personal experience and knowledge of the fauna present in French Polynesia.

The mite, chironomids and the moth larvae were not taken down to the species level due to a lack of knowledge in the area. The specimens were however counted in each sample to determine their abundance.

Data analysis

The dataset used for the analysis was the level of abundance of the specimens present at each depth level, along with the identified beetle species. As the project focus was on identifying species changes and levels of abundance over time in relation to human colonisation, we have compared three time periods:

1. The Pre-human period: Only indigenous and endemic Raivavae species present

2. The Polynesian period: Represented by a range of species present that are known to be Polynesian introductions.

3. The European period: Indicated by the occurrence of species known to be European introductions.

RESULTS

I sorted a total of 10 samples ranging in depth from 0 cm to 185 cm. The fragment sorting resulted in the documentation of 38 moth larvae, 159 mites and 252 chironomids. Collectively there were nearly 80 arthropod species identified.

Key Features of the Fossil Sequence

The fossil sequence of the sample collected displays major composition change at around 1250 Cal BP (Figure 3). This change in the species present and their abundance signals a change from indigenous taxa to one that is largely dominated by introduced species. Many native species disappear due to an inability to adapt to the changes to their environment and competition from the exotic species. These non-indigenous species are consistent with the arrival of Polynesians. At 1800 Cal BP (Figure 3) there is another key change in the composition, with virtually no native species being seen, a reduction in the amount of introduced Polynesian species and the introduction of an even newer set of species. These new species are reflective of the time, as there would have been a drastic increase in the number of visitors to the area due to human developments such as trade and slavery. These species are classified as European introductions.

 

Figure2. Summary diagram showing the change in indigenous, Polynesian and European species composition and abundance

Figure3. Diagram showing the complete record of arthropods identified and counted from the core sample. This diagram also displays the transitions between the pre-human, Polynesian and European periods


DISCUSSION

As aforementioned, Raivavae displays similar composition and transition to that of other records from the region. The observed periods (pre-human, Polynesian and European) can also be seen at around the same time as Tubuai, Rapa and Rimatara in the Australs and from Atiu in the Cooks (Pratt, 2011). Due to the habitat changes made by the arrival of humans, it is not surprising that some of the native species disappeared from the record.

Species dependant on aquatic habitats such as the chironomids responded positively to the habitat modifications brought about by the Polynesians. Whilst their abundance is quite limited throughout the record, their numbers reach a peak in the 80-85 cm depth sample. This depth is consistent with the Polynesian period and so their sudden influx can be understood.

Other species such as the moth larvae remain reasonably constant throughout the record with little changes to their abundance. This could indicate that the species of moth larvae present were not greatly affected by the habitat changes that occurred. Further research could be done in this area to determine whether this is the case however the first step would be to identify all of the individuals down to the species level to see which ones are present.

The mites found in the record show no clear correlation between their abundance and the habitat changes. The frequency in which they appear in the record fluctuates up and down between 5 and 38. Further research could be done in this area to see if there are any changes to the abundance of particular species however these would need to be identified initially.

The most species richness and abundance is evidently displayed by the beetles in the record (figure 3). As the beetles have been identified down to the species level, a clear image of the variations throughout the record can be seen. Certain species such as Pheidole umbonata are present in the pre-human period and manage to withstand some of the environmental changes that came about with the arrival of humans, as they are also present in the Polynesian period. However they then disappear once we reach the European period. Whilst there are some species that remain constant throughout all of the periods, including Hemi veliid and Hydro enochrus, most commonly, the pre-human species have a reduced abundance in the Polynesian period and then they become extinct by the time you get to the European period. This could be due to competition from species introduced by the Europeans but further research would need to be conducted to determine if this was the case.

CONCLUSION 

This project has provided insight into the colonisation of Raivavae and the composition of the species richness and abundance present. It has validated that arthropod records can be an extremely useful too in determining when humans colonised remote islands in the Australs. The record undisputedly shows the transition from the pre-human period to the Polynesian period on Raivavae. This transition was comprised of the native species becoming less frequent of extinct due to major ecological modifications. In addition, there is also a clear transition that can be seen from the Polynesian to the European periods. This change over time was characterised by the pre-human species being virtually non-existent, a steady influx of Polynesian species present but also the introduction of a number of foreign species. 

The use of arthropod fossil specimens as a way of determining human colonisation has been successfully demonstrated throughout this project. These transitional fossils have shown how valuable core samples can be in analysing the composition of an island and assessing its changes over time.

BIBLIOGRAPHY

Anderson, A. (2008) The Rat And The Octopus Initial Human Colonization And The Prehistoric Introductions of Domestic Animals To Remote Oceania. Biological Invasions, Volume 11, Pages 1503-1519.

Kirsch, P. (2003) Introduction to pacific island archaeology. [Online] Pacific Island Archaeology, Berkeley University. Available from: http://arf.berkeley.edu/projects/oal/background/pacislands.htm [Accessed 15th October 2011].

Porch, N. (2009) Insect Identification Guide. Raivavae, Austral Islands.

Pratt, P. (2011) Prehistoric-Modern Human Impact on the Insect Diversity of Mangaia (Cook Islands). Melbourne, Deakin University.