Evolution of New Zealand Plants and Animals

Achievement standard and links to past papers with answers
Crossword revision puzzle (vocab) Revision questions
New: revise both Geology and Evolution/NZ Endemic with this video - Moa's Ark. Presented by David Bellamy, world famous botanist. It's a bit dated but the science is still fine. This very amusing video shows that male kakapo aren't the brightet - they don't appear to be able to tell the difference between a human head and a female kakapo (may possibly offend some people though). Not nice for Steven Fry though - they have sharp claws.
Another good video resource is Ghosts of Gondwana from NZ onscreen (some may have the DVD from Wild South). Not to be confused with the book of the same name, referenced at the bottom of the page, but covering a similar scope.

Zealandia continent
Zealandia continent
Introduction
New Zealand was the last major landmass on Earth (apart from Antarctica) to be settled by humans. As little as 1000 years ago, no human being had ever visited these islands and none of our many 'hanger on' species, such as rats, existed here.
In the picture on the right, the light blue area represents the mostly submerged continent of Zealandia, a landmass that broke away from Gondwana some eighty million years ago. Because this separation came at a critical point in the Earth's evolutionary history - before the death of the dinosaurs, before the modern placental mammals had become widespread - our flora and fauna have some unique characteristics.
It is no accident that many of the background shots for 'Walking with Dinosaurs' were filmed here. New Zealand is literally 'the land that time forgot', protected, not by kilometre high cliffs as in Sir Arthur Conan Doyle's famous book "The Lost World", but much more effectively by over two thousand kilometres of forbidding ocean.
In this unit we will examine the endemic flora and flora of New Zealand. Endemic means found only in one place - in this case - New Zealand. We will look at the geological and biological origins of endemic NZ species and how these organisms have evolved over millions of years. We will also look at the biological mechanisms by which evolution happens, and the different roles that organisms play in a community.

1.1 Natural Selection

Natural selection is the term we use to describe a process in which more “fit” members of a species survive to produce offspring which inherit the characteristics which make them successful. The more fit individuals could also simply be more successful at reproducing to produce offspring which survive. “Fitness” is a term used to describe how well an organism is adapted to the conditions in which it lives.
Because there is variation among the members of a species, some individuals are likely to be more fit for particular conditions than others. Since these individuals reproduce more successfully, and pass on their characteristics, eventually the whole reproductive group will have the characteristics which improve fitness. Therefore these characteristics have been selected, and the conditions that produce them are termed selection pressures.
Darwin, age 51 (Wikimedia)
Darwin, age 51 (Wikimedia)
In 1859, Charles Darwin published a book, On the Origin of Species, in which he proposed that it was through selection acting in a variety of ways that different species arise from a common ancestor. Over time new species evolve to exploit new opportunities in an ecosystem, or species change to adapt to changing conditions. The term that is used for this overall process of change over time is evolution. Darwin’s theory is now accepted by the vast majority of the scientific community and is supported by a mass of evidence in the form of fossils, genetics, experiments and observations of organisms and biological communities.
Overall, the theories of natural selection and evolution can be used as a scientific model, so that with an understanding of the model we can make hypotheses and predictions about :
  • the relationships between organisms (contemporary or ancestral)
  • the purpose of special features of an organism
  • how the special features came about

In this unit we will be applying the evolutionary model to develop an understanding of the special features of endemic plants and animals of New Zealand, and how these came about.

Types of selection pressure:

Selection pressures can be the result of two types of environmental factor
Biotic (Biological) factors: these are environmental factors that result from the interaction of different organisms. They can include: predation, disease, competition, population pressure. For example, the lack of ground predators in NZ led to it being an advantage to have long lifespan and produce few young at a time but over a long period. This 'makes sense' if you don't have a high chance of being eaten; animals which have a high risk of predation have as many young as possible as quickly as possible before they get eaten, with lots of young increasing the chance of one surviving. In NZ, having fewer young meant that parents could invest more energy in nurturing them, decreasing their chance of dying as a result of starvation or disease.
Abiotic (such as geological) factors: these are the ones that are the result of non-biological agents. Examples include climate change, orogeny and continental drift (causing isolation). The main geological factors that influenced NZ evolution can fairly easily be worked out from your knowledge of the geology unit in this course. They include
  • Opeining up of the Tasman Sea (leading to isolation), so that many niches in NZ that are elsewhere filled by mammals are here filled by birds and insects (adaptive radiation). Time - 80 million years ago.
  • Inundation of NZ/loss of land area prior to the Kaikoura Orogeny (leading to a bottleneck). Time - about 35-25 million years ago.
  • Rise of the Southern Alps and other mountain areas (leading to a new habitat: alpine as opposed to forest). Time: 5-2 million years ago.
  • Ice Ages/climate cooling: leading to reduction of forest cover, loss of forest continuity (giving rise to isolation) and formation of new habitat types (non-forest) leading to adaptive radiation. Time: 2 million years to 20,000 years ago.

When different selection pressures act on different parts of a population, this is known as differential selection pressure. An example would be the different selection pressure acting on the ancestral kea/kaka population, with those in the mountain environment being selected for the traits that allowed survival in the harsh environment (e.g. wider foraging habits, aggressiveness) so that these birds evolved into the kea; those that continued to live in the forest evolved into the kaka.

1.2 Species

It is difficult to give a definition of species which is both simple and exact. In general terms, biologists use the term species to describe a group of organisms (population) that can actually or potentially interbreed to produce fertile offspring. There are difficulties with this definition, not the least of which is that it only applies to organisms that reproduce sexually. However, as a starting point for the organisms in which we are interested in this unit it is useful.

Binomial names

Kaka
Kaka
Biologists us a binomial naming system for species, in which the name has two parts. The first part of the name is the genus, and closely related species will belong to the same genus. For example, the kea (Nestor notabilis) and the kaka (Nestor meridionalis) are closely related species that evolved from a common ancestor, and their similar features led to their both being included in the genus Nestor. Note that this ancestor was neither a kea or a kaka, but more closely resembles a kaka because its habitat was identical and therefore it had identical adaptations.
kea.jpg
Kea
The science of classification as family, genus, species and so on is termed taxonomy.
Binomial species names are “latinized” (i.e. follow Latin grammar), and often relate to a characteristic of the organism or to a person such as the discoverer. For example, a member of the pohutukawa/rata family Metrosideros was discovered by the then HOD Science at Sacred Heart College, John Bartlett, and was named after him by the botanist who defined it - its name is Metrosideros bartlettii, and its common name is Bartlett's rata.
Writing binomial names:
bartlettrata.jpg
Bartlett's Rata

When referring to several members of the same genus, or to a particular species several times in an essay, it is acceptable practice to shorten the genus name to a letter followed by a period after the first use e.g M. bartlettii. The genus always begins with a capital and the species with a lowercase letter. When typing, binomial names should be in italics, and if handwritten should be underlined. In thes pages they are underlined where they are hyperlinked because wikispaces forces this when hyperlinking.

Subspecies

Some species are further broken down into subspecies. For instance the kaka has two recognized subspecies, the North Island and the South Island kaka. There is not such a clear definition of what constitutes a subspecies in biology, but for most NZ species the subspecies have different geographic distribution and some difference in morphology (which means the shape of the visible features), by which they can be distinguished. The scientific names of subspecies are given by adding a third part to the binomial name; for instance, the North Island kaka is Nestor meridionalis septentrionalis (the South Island kaka is known as Nestor meridionalis meridionalis; the species name is repeated because it is the “original” version whose characteristics were used to define the species).
In plants the term variety is used rather than subspecies; for example, there is a variety of pohutukawa (Metrosideros excelsa) with variegated (multicoloured) leaves known as M. excelsa variegata. Subspecies and varieties usually arise from some sort of genetic isolation (see section 1.7).
A cross between two species is called a hybrid. These are more common in plants than animals. For example, pohutukawa, M. excelsa and rata (M. robusta) can cross to form a hybrid. Such hybrids are (usually) infertile, which helps maintain genetic isolation.

1.3 Adaptations
cabbagetree.jpg
Cabbage tree

Adaptations are the special features of an organism which help it to survive. Biologists usually classify adaptations into three categories: structural, functional and behavioural.

  • Structural adaptations are those related to the organisms structure, such as the large feet of the pukeko, which help spread its weight on the soft surfaces common to its swamp habitat.
  • Functional adaptations are those that relate to the organism’s overall physiology, such as the rapid heartbeat of small birds or the sugary sap of a cabbage tree. Sometimes they are a little difficult to tell from structural adaptations.
  • Behavioural/response adaptations are those that relate to an organisms’ behaviour or responses, such as the light-seeking growth of a plant or the fact that kiwi are active at night and seclude themselves in burrows or holes during the day.




1.4 Genetic variation and inheritancenormal_curve.png

Organisms in a population do not have identical genes (unless they have been propagated asexually or have been produced from the same zygote). These small differences in genotype can result in small differences in the overall physiology of the individual (the phenotype).

Continuous variation: Characteristics which are controlled by many genes, such as the height of a human, are subject to continuous variation. In humans, the proportions of several body parts as well as various growth factors control size, and these are all coded for by different genes. An individual inherits different combinations of these genes from their parents, and there are many possible combinations resulting in a range of possible outcomes.Each individual gene has a particular probability of being inherited, so to be extra tall you would have to inherit all the possible tall genes. This has a much lower probability than inheriting some tall and some short genes. Continuous variation thus shows a normal distribution of possible outcomes, such as the one shown above right. More people are close to the average because this is where you get a mix of positive and negative factors.
Imagine rolling ten dice and adding up the numbers. The highest total you can get is sixty and the lowest ten. However, totals nearer the highest and lowest values are going to happen far less often than totals in the middle. If you rolled the ten dice often enough (e.g. 500 times) and drew a bar graph of how many times you got each total, from 10 to 60, you would get a shape very much like the one above.

Discrete variation: Other characteristics, such as purple or white flowers in
Purple and white agapanthus
Purple and white agapanthus
Agapanthus are subject to discrete variation. These are controlled by a single gene which the individual either inherits or does not, or else, the gene for the characteristic comes in two forms, one of which will always show up in the phenotype if that gene is inherited. These characteristics are said to be dominant; they show up regardless of whether the individual has two copies or just one of them. You will have learned how to predict the outcome of crosses of this sort in Achievement Standard Science 1.3.
stopkauridieback.jpg
Genetic diversity can reduce the impact of disease
There are other characteristics which are the result of the interaction of a small number of genes and have predictable outcomes in crossing, but are more complex than the simple dominant/recessive (Mendelian) crosses to work out. Students doing biology will learn about these.

The gene pool: The overall variation within a population’s genes is sometimes referred to as its genetic diversity, and the range of various genes available is termed the gene pool. Various factors in the environment can, at times, act to reduce the genetic diversity of a population, usually by reducing the gene pool as a result of a large reduction in population. The consequences of this will be discussed later.
In recent years much more attention has been paid to genetic diversity when human intervention is required to prevent the extinction of endangered species and maintain “species authenticity”. For example, during conservation work to restore kauri forest to the Coromandel ranges, workers have been careful to use seed taken from the surviving Coromandel trees in order to preserve the genetic identity of this forest as distinct from Northland kauri forest. If Northland seed had been used the genetic diversity of the kauri could potentially have been reduced. Such diversity may be important - for instance, some kauri may be more resistant to the kauri dieback disease that is presently threatening this tree. If they were a clones or highly inbred, like may of our cultivated pines, the impact of the disease might be even worse..

1.5 Mutation

The genetic code in a single cell in an organism can change as a result of a number of factors – e.g.
- exposure to radiation (natural or manmade),
- exposure to naturally occurring or manmade chemicals,
- the action of certain viruses, or
- “transcription errors” during cell division.
These changes are called mutations. They can occur in body (somatic) cells or in reproductive (germline) cells. Only mutations in germline cells are passed on to offpring.
Such mutations are random, and therefore most have no effect or are harmful. Harmful mutations will be rapidly selected against, and disappear from the gene pool. Some have little harmful effect and contribute to genetic variation. If conditions are right, some of the genetic variations may be helpful, and will be selected for by natural selection. This will see the mutation spread into the gene pool.
Human use of artificial mutations: One of the methods of creating new crop varieties without inserting genes from other organisms involves exposing seeds to levels of radiation sufficient to cause mutations, and raising the resulting plants. Although the vast majority do not have useful mutations, any that do can be interbred to pass on the mutation and create a new variety.
Mutations and species: The accumulation of genetic change (mutations) in a population is known as genetic drift. Although the species may continue to look and behave similarly, the accumulation of random mutations means that the descendants will be different from the ancestors. If there are two or more descendant populations isolated from each other, the degree of genetic difference between them will prevent them interbreeding even if they meet again later. This is one way different species arise. An example would be some of the different species of kiwi..
The myth of 'new information': creationists who try to discredit evolutionary theory often argue that mutation cannot create the 'new information' necessary to form a new species - some use a misunderstanding of the law of entropy (that things tend to get more random over time) to further this argument. It is (typically for this sort of pseudo-science) not a real argument. If you had a computer randomly generating letters, and a second computer programmed with some rules about the way that letters must fit together (e.g.you don't get sequences of consonents like 'tps' without a vowel in there somewhere) discarding letter combinations that 'don't work' and keeping ones that do, you would get some words. Further computers and more rules could generate phrases and so on. Is that new information? No. It is application of 'mutation' and rules. The 'rules' that generate the 'new information' in evoluton are a combination of chemical and biological laws that govern how living things work and interact. Selection (the censor computer) 'discards' the ones that don't work. The law of entropy hasn't been broken, because the amount of random code generated is far larger than the tiny proportion left by natural selection.

1.6 Niches

kauri.jpg
Kauri are canopy trees. They can support epiphytes.
An organism’s “job” in a community is commonly known as its ecological niche. For example, within a forest plant community you will have canopy trees, sub-canopy, undergrowth, epiphyte and so on. However, niches can specialize far more than described by these general terms and organisms often will specialize to avoid excessive competition (this is a selection pressure). So a group of birds might specialize to utilize different types of seeds, or plants might specialize for particular conditions (e.g a stream bank that has more light than the forest floor but insufficient space or soil to allow canopy trees to develop).
Adaptive radiation: There are circumstances in which new opportunities for niches may arise with no opportunity for organisms from elsewhere to migrate in and exploit them. For example, a new volcanic island may appear a long way from any other landmass. When this happens, organisms which do arrive (e.g, birds blown by a storm) may be able to evolve to fill a niche for which there is no existing exploiter. An example of this is the way that birds (moa) in New Zealand adapted to fill the niches which, elsewhere in the world, are normally filled by browsing mammals. This adaptation to fill newly available niches is called adaptive radiation and will be discussed in more detail later.
external image Phormiumtenaxflowertui.jpgCoevolution is a special case of this when organisms evolve together into a particular relationship. It may benefit both organsms, as in the relationship between the curvature of the flax flower and the tui beak (pictured).

1.7 Genetic isolation

The development of separate species requires some sort of isolation which stops the flow of genetic material throughout the whole of the species. Unless such a barrier to gene flow exists, the interbreeding of the members of a species will ensure a degree of genetic uniformity throughout the population effectively keeping them as a species.
Things that can act as a barrier to gene flow: Something as simple as wide geographical spread can limit gene flow, depending on how reproduction works for that species. For example, if pollination in a plant is by wind the pollen from widely separate plants can fertilize other plants and keep up gene flow. But if pollination is by insect, it is possible that the pollen may be confined to quite a local area. The rate of gene flow through the population may be sufficiently slow that genetic drift (as described in the section on mutation) may accumulate to the point where there is a difference across the geographical distribution of a population.
Initially, this may lead to subspecies where reproduction is still possible if somehow the populations are re-combined. The differences between the sub-populations may be gradual between the extremes. Under the right circumstances, where gene flow is limited for long enough, the genetic drift may continue where interbreeding between subspecies to produce fertile offspring is no longer possible. Thus a new species develops.
A wide geographic spread itself can lead to genetic isolation. For example, if a species has a short breeding season the breeding time may arrive at different times for a northern and southern population, preventing interbreeding.
Geological factors often lead to genetic isolation. The opening up of the Tasman Sea genetically isolated many NZ plants and animals from their overseas cousins. This is one of the reasons we have so many endemic species (a high level of endemism)
There are also special circumstances where factors contribute to species developing either more rapidly or in a more pronounced way. Some of these are outlined in the next sections.

1.8 Bottleneck effect

Population_bottleneck.pngThe bottleneck effect refers to a big reduction in population for a period of time. This means that genetic diversity is also reduced. A common cause is habitat reduction (e.g. due to climate change), but disease or the introduction of a new competitor or predator may also cause this. For example, during the Ice Ages (Pleistocene, or glaciations which happened several times in the last two million years) the area of forest in New Zealand was greatly reduced, particularly in the South Island. Forest remained only in low lying areas (though there were somewhat more of these due to the simultaneous reduction in sea level). Remaining forest cover was no longer continuous, as forested areas were divided by highlands of tussock and alpine vegetation. As a result, many populations of native plants and animals were greatly reduced and isolated from each other, and new species developed.
Not all populations would recover from the 'bottleneck event', in which case the species would become extinct.


1.9 Founder effect

This is the term used to describe the situation where a population is founded by a very small number of ancestors, such as a single breeding pair, or a single seed of a plant capable of self-fertilization. When this occurs, any genetic traits particular to the ancestor/s are likely to be preserved in the entire descendent population. Recessive traits will be common because of the large amount of homozygosity (i.e. genetic traits in which the same trait is inherited from both parents and is present in both gametes).
An example is the Chatham Island black robin. These were probably established in the last few thousand years by just a few birds blown out to sea and lucky enough to find land rather than perish. The Chathams are a very small target in a large ocean, so the chances of this occurring are small and so it occurs infrequently. The total population on the islands is also small. If any of the Chatham subspecies are blown back to the mainland (which also won’t happen frequently because the island population is small compared to the mainland one) they will find themselves in a much larger population of robins, so the genes they bring with them (which result in the black colour of the island robin, as opposed to the brown of the mainland one) will be greatly “diluted” and will have little effect on the whole population. For this reason, the Chatham Island robin has formed a distinct subspecies with a black coloration.

Section 2: Origins of New Zealand plants and animals

2.1 Introduction

NZ plants and animals (or flora and fauna) can be divided into four broad groups.
remnantcay.jpg
A cay. NZ 25 million years ago?

1. The flora and fauna that were carried with NZ when it split from Gondwanaland some 80 million years ago. By about 75 million years the proto-Tasman sea would have been sufficiently wide to prevent further arrivals save for basically the same sorts of things which can still come to NZ by natural mechanisms.
The species that either came with us from Gondwana, or show strong Gondwana connections, are sometimes referred to as the Gondwana remnant flora and fauna. Some scientists think that all of the present-day NZ landmass was submerged about 35 million years ago (during the Oligocene), and all that NZ flora and fauna has therefore arrived from elsewhere. But, regardless of this argument, there are (particularly for flora) a good range of species with clear links to Gondwana forms known from fossil evidence, and which are only found in NZ. Life may have survived on small cays, like the one o the left.. It would be very suprising if the tuatara, for example, came from somewhere else since the pre-Kaikoura inundation. They have no relatives elsewhere, and there are fossils of them found here (see discussion here)


.
Brown Teal, a flightless duck
Brown Teal, a flightless duck

2. Animals and that have arrived here since the split from Gondwanaland. These need to be able to survive a journey across several thousand kilometres of ocean. The fauna is mostly aerial – birds, bats and flying insects. But some non-flying insects and reptiles seem to have arrived on driftwood masses, probably washed out to sea during floods in Australia or elsewhere in the South Pacific. More plants have arrived since the Gondwana split, arriving as wind-blown seeds or seeds stuck to, or in the droppings of, migratory birds. Many of these species are subject to a strong founder effect. Our native flightless ducks such as the Brown Teal (illustrated above) would be an example. Their flightlessness ensures they are now endemic.


3. Migratory birds and marine/amphibious species. Animals that are not exclusive to NZ fall outside the scope of our study, but some of these animals have “settled” in NZ and evolved into forms that are now endemic e.g. the Hector’s Dolphin.
4. Organisms brought here by human agency e.g. the kiore, kumara and opossums. We are not examining the evolution of these species, although in the case studies we will look at some of the ecosystem change wrought by them.



2.2 The Gondwana remnants

Break up of Gondwana: external image Tuatara.jpgNew Zealand began to split from the “eastern” coast of Gondwana about 80 million years ago (see the Geology section). The split would have begun as a rift valley, similar to that which runs along the eastern part of the African continent today. This split would have widened into a narrow sea, similar to the Red Sea today, and then to a proper but small ocean. You will learn more details about this in the course for Achievement Standard 2.5 on the geological history of New Zealand. The significance for this unit is that, over time, it would have become progressively more difficult for organisms to travel between NZ and the Gondwana mainland.
Significance of the time: The time of the proto-New Zealand continent’s split from Gondwanaland is the time we call the late Cretaceous – in fact, about the same time as the famous dinosaur, Tyrannosaurus rex appeared. However, this dinosaur never made it to NZ. The proto-NZ continent had been uplifted from the sea and formed mountainous terrain about 50 million years earlier, and at the time of the split had been significantly worn down in a process known as peneplenation (this will also be covered in more detail in the geology unit). However, much of present day NZ was still above water at the time and the fossil record of it is therefore poor. Knowledge of the flora and fauna in the time immediately after the split is still very sparse, but we now know enough to describe it as a distinctly Zealandian rather than a Gondwanan biota. It was probably rather different from that of today - the great drowning before the Kaikoura Orogeny ensured that much of it is gone.
Allosaurs were found in Gondwana
Allosaurs were found in Gondwana
NZ dinosaurs:
Dinosaur fossils in NZ are uncommon, but they do exist, so some came with us when we broke away.The event(s) which caused the extinction of the dinosaurs occurred 5 million years before the Tasman Sea reached its present width; the “K-T boundary” event, as it is known, occurred 65 million years ago and the Tasman stopped widening some 60 million years ago. Though whatever caused the boundary events happened far away from NZ, the geological record here shows an unusual layer of clay at exactly this time. Above (i.e. after) this clay layer, there are some profound changes in the fossil record which suggests that, even here, this event caused widespread extinction. There is no evidence that any NZ dinosaurs survived this extinction event.

Mammals: There are no known mammal fossils from the late Cretaceous in NZ, even though mammals had appeared elsewhere. However, a fossil mammal from about 20 million years ago seems to indicate that some mammals may have come with us in the Zealandian fauna when Gondwana broke up, but have since become extinct. This mammal belongs to a completely separate mammal group, just as the tuatara belongs to its own class in the reptiles with no relatives anywhere else in the world.

Plant fossils: a few coal beds which contain plant fossils give us important clues about the relationship between present day NZ plants and those of this era. As well as this, there are plant fossils elsewhere in the world showing us very clearly that much of the flora of the three dominant forest types (kauri, podocarp and beech) of NZ is little changed from that of the early to mid-Cretaceous. NZ is truly, in this sense, “the land that time forgot”. This is why quite a few episodes of “Walking with dinosaurs” were shot here – there are few other places in the world which so closely resemble the way things were in the age of the dinosaurs.
After New Zealand reached its present position it continued to erode away. This caused the land to lose reliehills and valleys), and the resulting flat landscape became extensively swampy by about 45 million years ago. Gondwana remnant trees similar to the modern kahikatea dominated; this swampland eventually formed the coal measures of the Waikato, Southland and elsewhere. The subdued landscape eventually mostly submerged below the sea, leaving only a few small islands. These islands were not able to contribute much sediment, so the only rock-forming material from this era was shellbeds, forming the extensive Oligocene limestones in which most NZ caves are found.


The great drowning: The Oligocene submergence would have caused a very strong bottleneck effect, leaving only a few survivors. Biologists and geologists remain divided about which modern NZ species are Zealandian and which are post-drowning immigrants.
Among the most likely Gondwana remnants which survived are the tuatara and the weta; these seem to have changed little from the Cretaceous, probably because no strong selection pressures acted on them to do so.
Another Gondwana remnant which also survived the Oligocene bottleneck was the moa. Adaptive radiation seems to have caused this class of ratites to speciate to fill niches that in most places are filled by mammals.
Some scientists argue that none of present day NZ was land during the Oligocene. The arguments are complex, based on geology and biology. Given some of the constraints (moa completely lack even remnant wings, so they could not have flown here and they are probably too large to have rafted here on driftwood masses), it seems likely that even if this were the case there must have been parts of the NZ continent above water at this time, possibly parts which are now submerged (about ¾ of continental NZ is presently underwater). This Oligocene landscape must have been connected for a time to the parts of NZ which were uplifted and became land 22 million years ago in the Miocene.
Some of the NZ Gondwana remnant flora and fauna is closely related to species found in places such as Norfolk Island, New Caledonia and Papua New Guinea. These places were part of the same eastern Gondwana bloc that NZ originated from, supporting the idea that they originated from similar populations. For example, the kauri has close relatives on Norfolk Island and in New Caledonia.
Some of the main categories of Gondwana remnant biota:

Gondwana species
Flora:
· Conifer (kauri), podocarp and beech (Nothofagus) trees
· Ferns, particularly tree ferns
· Possibly the nikau palm

Fauna:
· Moa
· Tuatara
· Weta
· Carnivorous land snails
· Giant worms
· Some frogs

3.3 Later arrivals
Takahe (Wikimedia)
Takahe (Wikimedia)
pukeko.jpg
Pukeko
Other species arrived in New Zealand after the separation from Gondwanaland. For example, the takahe has small remnant wings suggesting its ancestors possibly flew here; its relative, the pukeko, can fly and arrived more recently hand has close relatives in Australia. The NZ pukeko is a more reluctant flier than its Australian relative, suggesting that it is already evolving towards flightlessness like the takehe.
Other than by flight, some animals may have arrived on floating masses of driftwood. It is quite a well known phenomenon in large, flood-prone rivers for tangled masses of vegetation to be ripped up by floodwaters and carried out to sea. Sometimes these masses have “hitchhikers”. Mostly, they die before reaching another landmass, or they do not have a breeding partner.
The thing to keep in mind when thinking about this sort of occurrence is the sheer scope of geological time. Suppose a drifting mass containing a species capable of establishing in New Zealand arrives only once every ten thousand years. This still means it will happen about one hundred times in a million years. NZ separated from Gondwanaland 80 million years ago, so many such events could have occurred. In practice, events like this are highly random, but even very infrequent or unlikely occurrences can have a significant impact over millions of years.
Plants and animals which arrived here without human assistance have became adapted to the peculiar conditions found here, such as the absence of predatory mammals or of large mammalian herbivores. This has resulted in a number of highly unusual species, many of which have fared very poorly since the rampant introduction of new species by humans. Examples will be considered in the case study section.
Some arrivals have “arrived” more than once; for example, the takehe has descended from a common ancestor with the pukeko but arrived several million years ago and evolved into the flightless form. NZ pukeko are very similar to the Purple Swamp Hen found in Australia and elsewhere; they arrived in NZ of their own accord within the last million years and have evolved little.

Post Gondwana arrivals probably include (this list could use input from someone with more expertise than me)
Flora:
  • Most dicotyledons, including
    - flowering shrubs and trees e.g. Hebe, Metrosideros (rata family), Coprosma, Leptospermum (ti tree), Pittosporum etc.
    - NZ daisies, alpine-adapted groundcover
    - Mangroves (arrived 14,000 years ago)
  • Monocotyledons e.g Phormium (flax) and Cordelyne (cabbage tree), grasses (including raupo and tussocks), orchids, rengarenga

Fauna

  • · Flying birds (tui, waxeye, morepork etc.); many of these have diverged into completely separate species from their ancestors and some have become nearly flightless (e.g. weka)
  • Flightless birds which have descended from a flying ancestor e.g. takahe, kakapo, kiwi (whether or not kiwi ancestors flew is subject to debate, as is their origin)
  • Some non-migratory shorebirds descended from migratory ancestors
  • Many fresh-water and estuarine fish
  • Hector’s and Dusky dolphins
  • Lizards (skink and gecko) possibly (gecko might have come from Gondwana)


Brief notes on particular organisms mentioned in the Achievement Standard


Takahe
Takahe (Wikimedia)
Takahe (Wikimedia)
The takahe and the pukeko are both descendants of a bird found elsewhere in the Southern Hemisphere called the purple swamphen. This bird has arrived in NZ more than once, both times well after the break up of Gondwana. The older of the two arrivals gives us the takahe, whose ancestors likely arrived some millions of years ago. Although the ancestors of the takahe flew here, it evolved into a specialist niche as a tussock/grassland feeder (rather than a swamp animal like its ancestor). In this niche, large flight muscles are a therefore a disadvantage as it takes extra food to maintain them. Poor fliers therefore had a selection advantage - they needed less food and could invest more in their eggs and young. The takahe thus evolved into flightlessness.
The second arrival of the purple swamp hen has become the pukeko. It is a much more recent arrival (hundreds or thousands of years rather than millions), and is very similar to the form found in Australia and southern Africa. .Pukeko may be able to interbreed with their overseas cousins, although there is no evidence for this being common, and some genetic isolation may be occurring. Pukeko are considered a subspecies of the purple swamphen.
The distinction between takahe and pukeko may be a result of geological factors - the rise of the Southern Alps and climate change, leading to the availability of the new tussock/grassland habitat for the takahe. Competition (a biological factor) possibly led them to exploit the new habitat, and once they have adapted to this, genetic isolation may have ensured their individuality as a species.


Weta
external image Knights.weta.750pix.jpgThis flightless insect is unusally large. Because of the predator free environment, it was able to survive here (it is a Gondwana survivor). Weta have evolved to large sizes partly as a result of adaptive radiation, to fill the niche that elsewhere would be filled by small mammals or reptiles. Tuatara do predate on them, but their slow metabolism and breeding mean that they were in a biological equilibrium (by contrast, mammals that predate on weta would need to eat more of them because of their higher metabolic rate).
The weta shown to the right is the Poor Knights Island weta, one of the larger species. This one is 20cm long. Weta species and subspecies on offshore islands and other isolated habitats are common, and are an example of the effects of genetic isolation and differential selection pressures. These giant weta are close to the maximum size for insects - their relatively inefficient gas exchange and lack of internal skeleton means that sci-fi giant man-eating insects could not evolve (alas for Hollywood).
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Pingao / Pikao
external image rhizome2.jpgPingao is a native dune-grass. It has adapted to unique NZ conditions, in particular the lack of ground grazers such as sheep or rabbits. It is a 'keystone' species which supports numerous other organisms. It is now endangered because of competition with marram grass, a non-native, as well as the effects of introduced grazers. Like many endemic species, it has adapted to a slower growth and breeding cycle and can't compete with the faster growing introduced species.
For more information go to this page, from a DoC handbook on this grass.
Image from http://www.doc.govt.nz/templates/MultipageDocumentPage.aspx?id=39705





Short-tailed bat (Pekapeka-tou-poto)
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(click for original)
One of NZ's only land mammals. Short tailed bats would have arrived here by flight (likely blown by a storm, so would exhibit a strong founder effect). However, the lack of large flying insects in ancient NZ, which elsewhere form a major part of bat diet, meant that they evolved into a different niche. Short tailed bats spend much of their time on the ground and predate ground insects.The lack of ground predators helped make this possible - elsewhere, bats this size on the ground would be a quick meal for rats or similar mammals. This is why one species of this unique creature is now extinct.
(Image from TeAra website at: http://www.teara.govt.nz/TheBush/NativeBirdsAndBats/Bats/1/ENZ-Resources/Standard/5/en)



Pohutukawa and rata
external image Small_pohutukawa_in_full_bloom.jpg
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Northern Rata
These belong to a single genus, Metrosideros. Whether these are post Gondwana arrivals or Gondwana remnants is unclear, but the first seems likely given that the genus is widespread in the south Pacific, including in places such as volcanic islands where they must have arrived post Gondwana. Genetic studies indicate that these originated in New Zealand. Pohutukawa produce huge volumes of tiny, wind blown seeds which could easily spread elsewhere stuck to seabird feathers or similar.
The different Metrosideros species are an example of adaptive radiation. Pohutukawa are specialized for harsh, rocky coastal environments. Rata of various species are adapted for the forest environment. As they are rather vine-like, several species have evolved the ability to climb up large canopy trees as vines. They then strangle the host tree and become a canopy tree themselves.
Some of the speciation of Metrosideros is possibly a result of genetic isolation. The northern and southern rata possibly became separated when forest cover became discontinuous during the Ice Ages. Bartlett's rata in the Far North may be a result of the fact that the North Cape area was an island until sea-level changes built up the 90 mile beach tombolo. The similar colour of most Metrosideros flowers may be an example of the founder effect.

Tuatara
external image Tuatara.jpgThese are remnants of an order of reptiles that were common shortly after the Tuhua Orogeny. They are not lizards, but form their own special group within the reptiles. They are Gondwana remnants which have held on in NZ because of the lack of predators (and are one of the strong lines of evidence against complete submergence of Zealandia before the Kaikoura orogeny).Part of their adap
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Stephens Island (Geoff Higgins)
tation is very long life and slow reproductive rate. This would be a disadvantage if they had any chance of being eaten (which is why they are extinct on the mainland), but makes sense if they can be 'sure' the only cause of death is starvation, disease or old age. By slowing their metabolic rate and reproductive rate, the risk of starvation is minimised. Having a couple of offspring every few years over a century or so makes a lot of sense if you have a good chance of living that long.
Today, the largest remaining population of tuatara are on Stephens Island (right).


Kaka/kea
Kaka
Kaka
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Kea,
These birds are closely related. They evolved from a kaka-like ancestor as a result of reduction of forest cover in the ice age and the new opportunities of an alpine habitat as a result of the uplift of the Southern Alps. This resulted in adaptive radiation, with the kaka adapted to continue living in the forest habitat and the kea evolved to take advantage of the new alpine conditions. These conditions were harsh, leading to the legendary intelligence and adaptability of the kea as a way of solving the problems posed by such an environment.

Further reading:
Gibbs, George (2006): Ghosts of Godwana - The History of Life in New Zealand. Craig Potton Publishing . A very worthwhile read for those who aim to get Excellence in this standard and the geology one.