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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.
I am a PhD student at the University of Auckland, New
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.
The Dijkgraaf Genealogy page
Most of my time is taken up by PhD
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
This is me with one of the
I am holding a sprig of kohekohe flowers
There are actually three distinct parts to this
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.
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.
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.
The six bush patches mentioned before are in three
pairs, one of each pair has possum and rodent
Possums, and to a lesser extend, rodents cause more
damage to New Zealand forests than was initially
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
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://www.reocities.com/RainForest/7109/fruit.htm (Operation fruit) or you can email or fax
(09-373-7420, attn Astrid) me to get copies of the maps send
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
University of Auckland
PO Box 92019
Click here to see Curriculum
Dijkgraaf, A. (1994) "Propagation
and timber plantation potential of puriri (Vitex
lucens)" MSc Thesis Auckland University.
Dijkgraaf, A.C, Lewis, G.D &
Mitchell, N.D. (1995) "Chromosome number of the New
Zealand puriri, Vitex lucens Kirk" New Zealand
Journal of Botany 33 (3) :425-426.
Dykgraaf, A.C. (1992) "Princely
Zealand Geographic, January - March 1992,
Dijkgraaf, A. & Schneider,
M.(1994) "Flight of the bumblebee" New Zealand
Geographic, October - December 1994, :84-98
Dijkgraaf A.C. (1996) "It's all in
the timing" Forest & Bird, 280 :8
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