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Astrid Dijkgraaf's Personal Home Page

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Page last updated on 8 November 1998

Visit my PhD project page called Operation fruit, the species list for my PhD, and find out where these species live on the distribution map, or maybe you would like an explanation of scientific names.

To find out more about the sorts of things I enjoy doing look at the highlights pages. I've recently started working for the Department of Conservation. I'm hoping to keep an online diary about the more interesting aspects.

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I am a PhD student at the University of Auckland, New Zealand.

Hobbies and interests

I spend most of my time with research for my PhD, but I do occasionally indulge in some Ceroc dancing, juggling, reading of Science Fiction books or hunting relatives via the internet to add to our family tree. Feel free to share of my personal highlights. I am also the newsletter editor for the New Zealand Ecological Society, and have a page of ecology conference dates from around the world.

Genealogy The Dijkgraaf Genealogy page



Most of my time is taken up by PhD work.

The PhD is in biological sciences, or be more precise, in plant - animal interaction ecology. Essentially, I am looking at how a selection of native trees interacts with each other and how this affects native birds (and other animals). Now don't get any wild ideas, trees don't throw outrageous parties, their interactions are much more subtle than that and have been moulded through the centuries.

The theory being tested is that co-evolution has modified the fruiting and flowering patterns of New Zealand tree species so that both the original bird dispersers and the trees benefit. For more background on this theory refer to the pages associated with Operation fruit.

This is me with one of the seedfall traps.
I am holding a sprig of kohekohe flowers
Picture of me by a seedfall trap (45 K)
There are actually three distinct parts to this theory.

Part one
Firstly, I am looking at how tree species interact around the Auckland region. To do this I have set up seedfall traps (large square green funnels, like in the picture) in 6 different bush patches around the greater Auckland region. Every fortnight I visit each of these bush patches, clear the seedfall traps and take the material home to analyse. While I am wandering around in the bush I also observe what the selected trees are doing. I note whether these trees are fruiting or flowering, how much fruit or flowers they carry, and whether any of it is ripe.

This information has already told me that fruiting and flowering seasons of my target tree species are quite distinct and do not overlap in time. One plant will finish fruiting or flowering before the next one starts. However, the fruiting and flowering periods are arranged in such a way that there always is ripe fruit or open flowers to be found in that bush patch.

Part two
The second part of my thesis investigates the damage inflicted on this system by introduced animals. Before humans arrived here, New Zealand only had aquatic mammals and two species of small bat. This means that the larger fruited species were only ever dispersed by birds, and that most of the large nectar producing flowers are adapted for bird pollination. This system evolved in the absence of mammals and the trees have very little in the way of mammalian browser defences.

Humans brought with them mice, rats and possums, all voracious plant predators and they are thought to have a major impact on the forests of New Zealand. To measure the amount of damage done I poison possums, rats and mice in some of my bush patches and compare these "possum and rodent free" areas to neighbouring bush patches where no animal control is undertaken.
Possums eat leaves, mature and immature flowers and fruits. Look at the difference between the kohekohe inside the cage compared to that outside the cage. There are no flowers to be found outside the cage at all.Picture of chickenwire cage on kohekohe branch with flowers inside the cage but not outside (59 K)
The six bush patches mentioned before are in three pairs, one of each pair has possum and rodent control.
Possums, and to a lesser extend, rodents cause more damage to New Zealand forests than was initially anticipated.

Part three
Research to date shows that fruiting or flowering for some species is temperature cued, while others are cued by daylight length. New Zealand is a long narrow country, covering a wide range of latitudes and altitudes. This gives rise to great variation in temperatures and daylight hours and will affect the fruiting and flowering patterns of species.

An added complication is that not all of the species extend over the entire country. If you recall, we are working on the theory that plants have co-evolved with the surrounding species, so that only one species has ripe fruit or flowers at any particular time, and so that there is food for birds all year round. What happens to this nicely arranged pattern when some of the species dropout?

To tackle both these issues I have invited schools to join me in Operation fruit, where schools report what is happening to native species in their local area. The information is collected and maps are updated every fortnight and these are, and will be available on http://webspace.webring.com/people/gu/um_3981/fruit.htm (Operation fruit) or you can email or fax (09-373-7420, attn Astrid) me to get copies of the maps send to you.

This research is supported by grants from a number of conservation agencies and companies. To see who is helping me go to the supports page. If you would like to know more about what I am doing please feel free to drop me a line (postal address below).

Nice chatting with you.

Regards from Astrid Dijkgraaf.

School of Biological Sciences & School of Environmental and Marine Sciences
Tamaki Campus
University of Auckland
PO Box 92019
Auckland
New Zealand.

Click here to see Curriculum Vitae .

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