New Zealand has almost no native mammals; its larger animal life is dominated by birds, lizards, frogs, wētā and land snails. Many of these species and groups of species have unusual characteristics.
New Zealand’s plants and animals have similarities to those living on nearby southern land masses, which were once joined as the Gondwana supercontinent. For years scientists thought that many of New Zealand's life forms were primitive survivors, isolated since the country broke away from Gondwana about 85 million years ago. But new research has shown that many of today’s native species are more recent arrivals that came to New Zealand over large stretches of ocean.
There are three key questions about New Zealand’s plants and animals:
To answer these, we need to look at evolution, dispersal and extinction – the main processes that control biodiversity. These in turn are influenced by factors such as land area, soil, climate, isolation, tectonics and catastrophic events. The development of New Zealand’s plants and animals is strongly connected to the country's geological and climatic history.
Until recently, evidence that early mammals (monotremes) lived in New Zealand was purely circumstantial. Dinosaurs and mammals lived alongside each other in Gondwana 85 million years ago. Dinosaur fossils 65–75 million years old have been found in New Zealand, so scientists think that mammals may have also been present. A primitive mammal bone between 16 and 19 million years old was recently found in Central Otago, spectacularly confirming this hypothesis.
About 120 million years ago the land that was to become New Zealand was still part of Gondwana. It was mountainous, and lay within the Antarctic Circle (latitude 66° south). There was complete darkness for three months in winter and continuous sunlight during the short summers. The climate was cool but not cold. There were forests of tall conifers, including podocarps (relatives of the modern kauri, Agathis australis), Wollemi pine (Wollemia nobilis), and conifer relatives – ginkgo and groups that are now extinct. These trees grew above horsetails, mosses, liverworts and hornworts.
By 100 million years ago there were early flowering plants in the part of Gondwana that was to become New Zealand. A diverse forest developed – largely deciduous flowering trees and conifers. Not much is known about the land animals of the Cretaceous period (146–65 million years ago), but there were dinosaurs, birds, tuatara (Sphenodon) and geckos. It is likely that there were also freshwater crocodilians and early mammals (monotremes).
About 85 million years ago a large fragment of eastern Gondwana began to break away, and the sea flooded the rift, forming the Tasman Sea. This land mass, today's New Zealand, drifted north. By 55 million years ago it was located between latitudes 60° and 50° south. It lay 2,000 kilometres from eastern Australia, a distance it has more or less maintained ever since.
New Zealand was surrounded by warm temperate to subtropical waters. As the land moved north, marine corals and tropical mangroves fringed the shores, and tropical and subtropical-type forests dominated. The land was gradually flooded by the sea and worn down by erosion. As the landscape and climate changed, plants and animals evolved or became extinct.
For a long time New Zealand plants and animals were similar to those in Australia, as the climate and soils were alike. Typically, plants such as Casuarina (she-oaks), eucalypts (gum trees), Banksia (bottlebrushes) and Acacia (wattles) flourished in both lands.
By 5 million years ago Australia had moved northward into a drier subtropical zone. New Zealand lay further south in cooler, moister latitudes swept by westerly winds. Glaciers advanced and retreated as the climate repeatedly cooled and warmed.
New Zealand life forms which had adapted to warm temperate and subtropical conditions rapidly became extinct, and some distinctive groups evolved.
There has been much controversy about whether today’s native plants and animals are direct descendants of those on eastern Gondwana. Some New Zealand plants and animals evolved more than 85 million years ago – so they might already have been living there when the land split away. However, it is possible that they have not been in New Zealand continuously since the break-up, but spread later from other parts of Gondwana.
There is an excellent fossil record of flowering plants and conifers – making it easier to assess whether they have been in New Zealand continuously since it broke away from Gondwana, or arrived later. Recently, scientists have examined DNA differences between related species to estimate their age of origin.
Very few plants, if any, can be shown to have been continuously present. Many common plant families (for example, grasses, daisies and forget-me-nots) did not evolve until long after New Zealand had separated from Gondwana. They arrived by crossing the ocean.
Almost all living things contain DNA – the genetic blueprint that contains coded instructions as to how to make a particular species. The DNA of two different species can be compared to estimate how long ago they diverged from a common ancestor, on the basis that minor differences accumulate at a steady rate. This process is referred to as the molecular clock. The bigger the differences in DNA, the longer ago the two species diverged on separate evolutionary paths.
Even ancient groups may have arrived relatively recently. For years it was believed that southern beech (Nothofagus) had been in New Zealand for 85 million years. The presence of Nothofagus (or its fossil leaves) on many of the continental fragments of Gondwana (South America, Antarctica, Australia, New Caledonia and New Zealand) seemed to support this idea. The family Nothofagus has been in New Zealand for 85 million years, but fossil finds and DNA research suggest that today’s southern beech species are much younger. They evolved from an ancestor that arrived around 30–40 million years ago.
Animal groups may have evolved from life forms that were in New Zealand when it broke away from Gondwana. But so few fossils have been found that it is difficult to be sure. Groups that were probably part of the Gondwana fauna include tuatara, geckos, kākāpō, moa, wrens and some primitive groups of insects, spiders and earthworms.
Some of New Zealand’s plants and animals are primitive – but this does not mean they have been present for 85 million years. Some relatively primitive groups such as skinks and cicadas spread from New Caledonia and Australia. Skinks may have arrived around 30 million years ago, and cicadas within the last 24 million years.
It seems that the ancestors of many of New Zealand’s plants and animals made landfall long after the country split from Gondwana. This is astounding given the sheer distance between New Zealand and the nearest large land mass, Australia.
The ancestors of many of today’s native plants and animals arrived after New Zealand separated from Gondwana, around 85 million years ago. But how? There are many hundreds of kilometres of open ocean around New Zealand.
Plants have spread more successfully than animals. Most plants can survive for a long time as small seeds. They may be damaged and still survive, and they only need basic climate and soil requirements to start growing.
Species that are isolated in different environments for any length of time evolve into distinct forms. So, New Zealand species identical to those elsewhere must have arrived recently – or spread recently from New Zealand to other countries.
Native plants also found elsewhere are usually those that release microscopic spores (for example, mosses and ferns) and flowering plants with small seeds (such as orchids). Their spores and seeds are easily carried by wind. Wetland herbs are often dispersed by migratory birds carrying seeds and spores in mud on their feet or feathers. Forest trees with heavy seeds are less likely to spread from one land mass to another.
Animals often have more specific requirements than plants. While the vast majority of plants are hermaphrodites (they have both male and female reproductive organs), most animals are unisexual – which means they need both a male individual and a female individual to reproduce. Most animals need certain plants or prey for food, so these must be present for them to survive. Some, such as social insects, have complex social structures which make it unlikely that a few individuals could establish a new population. Only birds, or microscopic or asexual animals, disperse as easily as plants.
Animal species found both in New Zealand and other places can usually fly. These include birds (harrier, pūkeko), butterflies (monarch butterfly) and dragonflies. Strangely, few insects or spiders have arrived recently, even though many can fly and some are small enough to be carried by the wind.
Before the development of the Māui gas field off Taranaki, entomologists put insect traps on the drilling platforms. An amazing number of exhausted Australian moth and butterfly species, borne on trans-Tasman gales, were captured. Of the species caught, only a handful had successfully become established on mainland New Zealand.
Many plants and animals have arrived since New Zealand split from Gondwana, despite not having features that would normally make the journey possible. Skinks, for example, may have arrived about 30 million years ago, and buttercups only 5 million years ago. Chance transport by wind and bird movements is unlikely – but these species have arrived over tens of millions of years. Given enough time, even the improbable will happen.
Some species flew or blew to New Zealand. For animals that do not fly, only very rare and unusual events could have brought them to the country. They may have come on floating masses of earth, wood or plants, possibly washed out to sea in floods or tsunamis. Unusually strong and persistent winds or storms could have brought them to New Zealand.
Most New Zealand species are not very different from their close relatives in other countries. But some are primitive animals that have died out or are restricted elsewhere. Some have been in New Zealand for at least 85 million years. Others arrived after New Zealand split from Gondwana.
The speed with which introduced rats, mice, stoats and other mammalian predators have recently wiped out many native species gives a clue as to why primitive species endured for millions of years. On other land masses, more sophisticated competitors and predators evolved – primitive species became extinct as a result. These competitors and predators were absent in New Zealand, so primitive life flourished.
There are a number of primitive animals in New Zealand:
Few plants can be categorised as primitive survivors, although many are from old groups. Some of New Zealand’s primitive plants, such as the flowering plant hutu (Ascarina lucida), arrived recently (in the last 10 million years). Hutu is endemic – only found in New Zealand. Other primitive groups, such as podocarps, are widely distributed elsewhere.
Some features are shared by many New Zealand species, making the group distinctive. Examples are flightlessness in birds, gigantism in some animal groups, and white-flowered plants.
New Zealand, in common with other isolated archipelagos such as Hawaii, has a large number of radiations. This is when one species rapidly evolves into many species. These may be adapted to various environments, or have highly distinctive forms, behaviours or habitats.
Large, flightless animals generally cannot cross oceans. This explains why New Zealand has no land mammals, iguanas, land turtles and snakes. A number of advanced groups are missing among the ants, wasps, hornets and termites, including the most aggressive and destructive species.
Advanced groups of predators and competitors evolved elsewhere over the past 85 million years. But they could not cross the ocean and did not become established in New Zealand.
Birds had no predators on the ground; they were preyed upon by a range of small to very large predatory birds. So for most birds, flight was unnecessary – even risky. Before humans arrived, a quarter of New Zealand’s land and freshwater birds were flightless. Many more were poor fliers. As they did not need to be light enough to fly, most became larger than their flying relatives. Adaptations for self-defence were all geared towards predatory birds. They included limited flight, camouflage, ground nesting and freezing when disturbed.
Some animal groups proliferated in the absence of predators. New Zealand is home to more than 80 species of skinks and geckos, an extraordinary number for a coolish, temperate climate. The forest understorey, moss and litter habitat has over 1,400 species of snail. There are more than 1,800 moth species, and over 2,000 species of fly. This may be due to the lack of small mammal predators such as rats and mice, aggressive colonial ants, wasps and hornets, and competition from termites. Specialised invertebrates that feed on or parasitise snails are also largely absent.
New Zealand’s birds, bats and insects expanded into areas and ecological roles normally occupied by mammals. The kiwi has hair-like feathers, a keen sense of smell, and powerful digging feet. Nesting in a burrow, it is much like a badger.
Moa fed in forests and grasslands like goats, deer and cattle. They became very large, in order to better deal with a coarse vegetable diet. In place of mice, flightless wrens, ground-walking bats, large carnivorous Paryphanta land snails, and giant wētā (up to 70 grams in weight) fed on the insects and plants of the forest floor. The most likely explanation for gigantism is that greater size increased the range of foods animals could eat.
Flowers in other continents often have intricate shapes and bright colours. Most are bisexual, relying on animals to pollinate them. New Zealand lacks the main specialised flower pollinators – long-tongued bees, hawkmoths and hummingbirds. There are very few butterflies.
Plants with complex flowers that need specialised pollinators could not become established. They could not set seed or, if they did, the seed produced by self-pollination was inferior (as genetic material was not being exchanged between different plants). The failure of plants with complex flowers to grow, in turn, hindered the establishment of specialised pollinators.
Typically, native flowers are small (sometimes only a few millimetres in diameter), simple, and white or dull coloured. These blossoms are suited to New Zealand's main pollinators – small, short-tongued native bees, night-flying moths, flies and beetles. The flowers often have a strong scent to attract a wide range of pollinators. Lack of complex floral structures increases the risk of self-pollination. To help ensure that genetic material is exchanged between plants, many (23%) of New Zealand's flowering plant genera are unisexual, more than anywhere else.
New Zealand has mild winters, moderately warm summers, and well-distributed rainfall. The adaptations of plants and animals in more seasonal climates are absent. New Zealand's indigenous plants tend to be sensitive to frost and cold. Even some alpine plants such as New Zealand's Veronica (formerly Hebe) – popular in British gardens – cannot survive a cold British winter. Only a few native trees and shrubs lose their leaves in winter, and adaptations protecting plants from frost (such as hard cases covering winter buds) are uncommon.
New Zealand plants are mainly evergreen perennials. Annual herbs, or those that die back in winter and store their bulbs underground to re-sprout in spring, are uncommon. Similarly, few insects undergo diapause – a state of suspended development during unfavourable periods, which is a common adaptation in insects in highly seasonal climates.
Naturally-caused fires are rare in New Zealand, and few trees and shrubs have the defences common in fire-prone areas, such as thick bark, buds below the bark, large storage roots, and fire-promoted release of seeds. The woody plants that do have these features are usually of Australian origin (mānuka), or are closely related to Australian species (matagouri).
Dense, evergreen forests and lack of natural grasslands below the treeline are probably the reason for ‘insular woodiness’ – where herbaceous ancestors rapidly evolve into woody descendants. New Zealand has woody members of the daisy family, the carrot family and the plantain family, which are often herbaceous in temperate continental regions.
New Zealand’s largest flowering plant genus is Veronica, formerly Hebe, with 121 native species (hebes and their relatives). These plants, which range from small trees to alpine cushion plants and a tiny lake-shore herb, diversified from a single ancestor during the last 10 million years. Their ancestor was probably a low-growing northern hemisphere plant similar to the common speedwell (Veronica arvensis). It’s thought the evolution of woody hebes like Veronica stricta was aided by the familiar enclosed leaf buds, which give protection to the delicate stem tips.
Plant and animal groups on islands often undergo radiations – where one species rapidly evolves into many species that may live in different environments. On islands there are usually few plant and animal types, which reduces competition. Also, mountainous island archipelagos offer diverse habitats where new species can evolve.
New Zealand lost most of its Gondwanan plants and animals progressively as it sank into the ocean. Around 30 million years ago, the land area was probably less than 20% of its current size. Many groups of plants and animals became extinct or were greatly reduced. This was an advantage to species that persisted or were new to arrive.
For example, from a single moa ancestor, which lived around 30 million years ago, at least 10 moa species evolved. They differed in form and size (20–250 kilograms), and were present in all habitats from alpine zones to the coast.
Insect groups have also radiated into many specialised forms. Examples include cicadas (40 species) and wētā (70 species), which have species in all habitats from the seashore to mountain tops.
For many plant and animal groups the opportunity to radiate was provided by three factors:
Parrots and parakeets have adapted to New Zealand’s alpine and subantarctic environments. The world’s most southerly parrots and parakeets live on the subantarctic islands, and the kea is an alpine parrot.
New Zealand lizards are unusual in their tolerance of cool climates, having specific adaptations such as giving birth to live young (rather than laying eggs). Insects such as cicadas have invaded the alpine zone, which they do not do in other countries.
Many new, species-rich groups appear to have originated from long-distance dispersal. The herb Epilobium, originally from North America, arrived recently – probably in the last 3 million years. More than 40 species have radiated into numerous open and mountainous habitats. Ranunculus (buttercups), a diverse group found in mountains and subantarctic islands, arrived only 5 million years ago, and now there are more than 40 species with highly variable leaves.
Few of New Zealand’s plants and animals appear to be ancient remnants from Gondwana. Arrivals during the past 85 million years have rapidly evolved and radiated into different habitats and form many of the native land species.
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