Fruiting and flowering of native plant species.

Operation Fruit

Fruiting and flowering of native plant species.

Detectives wanted

Page last updated on 20 September 1998

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since July 11, 1997.

Major headings on this page

Setting the scene
Puzzle ingredients
Some of the answers
Also some unexpected results
That was in Auckland, what about the rest of New Zealand?
Looking for plant detectives
Become involved in a New Zealand wide science project

Associated pages.

There are a number of other pages associated with this main page, including a list of species included in Operation Fruit. From here you can also go to pages giving more details about some of the species.
You can go directly to the species distribution map for these species.
We will all be collecting information in the same week all over New Zealand to make sure that weather and climate do not affect our results. Click here to find out which week to collect data.
All plants have scientific names that look rather complicted if you are not used to them. This page explains why we use Latin names.
My personal homepage, explaining other parts of my thesis can be found here. To find out more about the sorts of things I enjoy doing look at the highlights pages. I've recently started a job, and hope to keep a sort of diary on the subject, have a look at the diary for more information.

Sign my Guestbook, View my Guestbook

Background

Helping each other.
Many plants, world wide, need animals to eat and spread seed around, or to pollinate the flowers. Scientists think that both the plants and animals benefit from this system. By eating the fruit the animals get food and plants have the seed spread around in faeces. This means that when the seed germinates, not only is it in a nice pile of manure, but it could be in a very nice place for a new plant to grow, much better, perhaps, that where the parent plant was. Animals collect nectar or pollen from flowers as another food source (think of bees for instance), they carry the pollen between flowers and plants and so pollinate the flowers. Successful pollination means that more seeds become fertile and this can mean more fruit and more seedlings.

Co-evolution.
Scientists think that such systems, where both plants and animals benefit, have developed (co-evolved) over time. Co-evolution means that animals or plants look or behave in a way that benefits other animals or plants. For instance, kowhai flowers are bright yellow to attract birds and have nectar as a food reward. Tuis know that bright colours (eg yellow, red orange) mean food, and they have long beaks and long brush-like tongues so that they can reach the nectar in the bottom of kowhai flowers.

Scientists think that co-evolution helped design fruit and flower features (such as colour, size, nutritional content, flower structure), fruiting and flowering patterns (crop size, ripening rates, timing), and some aspects of animal behaviour, looks and physiology.

The recipe for a nice simple puzzle;

1) Only a few species.
New Zealand is a great place to study plant-animal interactions like these and to get some idea of co-evolution. New Zealand, on a world wide scale, has a relatively few plants and animals and has been isolated from other continents of Gondwana for a long time. This has given plants and animals ample time to start working together.

2) Mainly birds.
There also are only a few classes of animals that can act as dispersers (spreading the seed around) and these are mainly birds and reptiles that simplifies our situation. Other countries have mammals, marsupials and large reptiles that also eat fruit, and that makes for a much more complicated puzzle.

3) No migration.
Quite often there also are migrating species (especially birds, but also animals like elephants, deer etc) that will eat fruit when visiting a country. Again this would complicate the puzzle enormously, because we would need to include the visitors' diets in our calculations. None of the migratory species that come to New Zealand are fruit eaters, so we don't have to worry about what these guys get up to.

4) Only vegetarians.
There were very few carnivorous species in New Zealand forests that we know of. There was a giant eagle, with a seven metre wingspan, and there still are native falcons and Australasian harriers, but most of the birds were vegetarian, eating fruit, leaves, flowers, nectar and pollen. So, it could well be that the fruit eaters living in New Zealand rely heavily on the native plants for food.

5) Lots of plants need birds.
We know that a high proportion (approximately 70%) of New Zealand plants relies on birds to dispersers its seed, so the native plants are very reliant on native birds for dispersal. This is even more extreme for large fruited species (fruit wider than about 1 cm in diameter). Now days only the native pigeon (kereru) can open its beak wide enough to swallow these fruits and spread the intact seeds around (only intact seed will germinate and produce a new plant). In the past other species, probably moa, might have eaten the fruit too, but we are not sure how good these birds were at spreading intact seed around because they had stones in their gizzard that could have damaged the seed.

6) Lots of birds need plants.
New Zealand has quite a high number of nectar feeding bird species but only relatively few plant species with nectar bearing flowers. Thus nectar bearing plant species could be in short supply and birds might really go for any of the species that have open flowers. There are many birds that include either fruit or flowers in their diet too, but only a few, like the kereru, never eat insects to supplement the diet.

Put all the above ingredients on an isolated island and leave to stew for several million years.
The above reasons mean that we might see a high degree of co-evolution. That is, many plants behave in a way that help birds, and many birds behave in a way that is useful to plants. Co-evolution would have developed because plants and animals had to rely on each other to survive.

We are finding some of the answers

Plants play tag.
Until recently, little was known about the timing of fruiting and flowering of our native tree species.
I have been studying native trees in bush patches around Auckland for the last two years and have been able to show that fruiting and flowering seasons of plant species are quite distinct and do not overlap in time. One plant will finish fruiting or flowering before the next one starts. This could have developed by plants competing for the services of pollinators and/or dispersers. In other words a long period of co-evolution between plants and animals might have encouraged plants to space their fruiting or flowering in time.

Diner is always served; but does it have to be spinach?!!
The effect of this is that there is always some ripe fruit available in the bush, but hardly ever more than one species at a time. This is useful for both plants and birds. The birds don't have to fly very far to find food, there is always something to eat locally. The plants benefit because they are the only ones with food available, so the birds have to dine in their branches, even when the fruit isn't that tasty.

A similar thing happens to flowering times too.

Some unexpected results.

Plants in hibernation.
One unexpected result was that some plant species (in particular tawa, taraire and karaka) can vary up to a month in the production of ripe fruit. Fruit in Wenderholm, 50 km North of Auckland, ripens about a month earlier than fruit in Whitford, 50 km South of Auckland. This might be because Whitford is usually a bit colder than Wenderholm, and these species might grow better at certain temperatures. We call this "temperature cued".

Don't wake me until the sun comes up.
Other species (kohekohe and kahikatea) produce fruit at exactly the same time at Wenderholm and Whitford. It could be that these trees don't grow much until they get a certain amount of light. During winter there is not enough light and the species don't get up to much. When the days get longer they start growing again. This is called "day-light length cued".

What happens in the rest of New Zealand?

The Mexican wave: the New Zealand plants' version.
New Zealand is a very long country and quite mountainous. This means that there could be quite a few differences in fruiting and flowering times around the country. Just by travelling around a bit you can discover that species usually start flowering or fruiting in the North and that a wave of flowering and fruiting gradually moves South.

Pockets of resistance.
This Mexican wave is not true for all species, however. I have been told that some species, for instance kowhai, have pockets of plants that don't fit the wave theory. These pockets flower well before the wave hits the local area. What is more, if you take one of these plants from such a pocket, and plant it elsewhere, it will still flower at the same time as the pocket, and not according to what the other kowhai around it are doing.

Dropouts
Just to add another complication, not all plant species are present over the entire length of New Zealand Click here to see species distribution map (9K). In fact, the further South, and the higher up, you go the less species you will find with large fruit. This is to be expected really. Large fruited species tend to come from tropical ancestors and don't like colder climates because they get frost bite. You can occasionally find some of these species planted in frost free areas of gardens.

If you recall, we are working on the theory that plants have co-evolved, with other plants around them, so that there is food for birds all year round and so that only one plant has ripe fruit or flowers at any particular time.

So what happens when you start losing some of the species from this nicely arranged pattern?

Looking for plant detectives.

The only way to solve some of the above problems is to look at a range of species all over New Zealand at the same time. Unfortunately, I can't be in all those different places at the same time.

But there are schools all over New Zealand, and some of these might want to help me by playing plant detective. This would involve looking at trees in your local area once a fortnight and telling me which ones have ripe fruit or open flowers. I am interested in about 30 different species and hopefully playing plant detective would not be too difficult or take too long.

How would it work?
Students or schools send their score to me (Astrid Dijkgraaf) by email, or fax and I will put all scores on a map of New Zealand. This map will be updated every fortnight and will be available on a World Wide Web page or send to all participating schools by fax or computer. Hopefully we will be able to see the Mexican "wave" of fruiting and flowering progress across New Zealand, and maybe even pick out pockets of resistance

Getting down to the hard Science.

Hypotheses.

Null-hypothesis: Fruiting or flowering of species X starts at the same time all over its range.

Alternative-hypothesis 1: Fruiting or flowering is triggered by a particular temperature. (We can test this by correlating local temperatures with starting times.)

Alternative-hypothesis 2: Fruiting or flowering is triggered by daylight length. (We can test this by comparing local day length with starting times.)

Alternative-hypothesis 3: Fruiting or flowering is competitive between species. (As species composition changes we would expect to see fruiting or flowering times changing to suit.)

There are multiple alternative hypotheses because there are multiple species to test the null-hypothesis on.

Method.

Simple scoring system
Students observe trees of the target species (see further below) every fortnight and assign a score for that area according to the following categories;

	1- 10 trees with open flowers or ripe fruit	11- 50 trees with open flowers or ripe fruit	more than 50 trees with open flowers or ripe fruit
Trees native to the area	1a	2a	3a
Planted trees	1b	2b	3b

Students send their score, eg kowhai flowering - 2b, 1a, to Astrid Dijkgraaf by email, or fax (09-373-7042). You can give two scores for the same species if you have both planted and naturally occuring plants of the species. Astrid will put all scores on a map of New Zealand. This map will be updated every fortnight and will be available on a World Wide Web page or send to all participating schools by fax or computer. Hopefully we will be able to see the Mexican "wave" of fruiting and flowering progress across New Zealand and determine which hypotheses are most appropriate.

Remember the pockets of resistance!
It is important to distinguish between planted trees and trees native to the area because of the pocket of resistance as explained earlier.
All plants in suburbs are probably planted, they might originally come from local seed or plants, but to be on the safe side they should go in the "Planted trees" category.
Use the "Trees native to the area category" if you can be quite sure that the trees you are looking at are native to the area, either because they are naturally established in a piece of native bush, or because somebody knows for sure that the trees came from a local seed source.

Sampling period.
I have set the sampling period at once a fortnight in particular weeks (click here to see collection) dates to make sure that differences in season don't affect the results too much. I found that this was the best spacing of observations because wider spacings can easily miss peak fruiting or flowering events. However, it is possible to reduce the sampling period to monthly observations (see collection dates below).

The species of interest.
(Click here to see species list.)
The survey is restricted to the larger fruited species (ie larger than 1 cm in diameter) and fleshy types to reduce the number of fruit species and because generally only a few species (and now only the native pigeon) could eat these large fruits. This restriction increases the chance of picking up co-evolutionary trends. The only exception will be kahikatea, nikau, and pigeonwood as these species are important food sources for pigeons.

Flowering species are mainly of 2 types, large tubular flowers that are thought to be pollinated by birds (though insect pollination cannot be excluded) and the more openly accessible flowers of the Metrosideros group. (A species list is included at the back.) Scientists think that tube like flowers and bright colours are a sign of co-evolution with birds.

I would like to go to the species list, the species distribution map, the collection dates, or an explanation of Latin names.

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