The 'biodiversity of New Zealand', a large
Pacific archipelago, is one of the most unusual on
Earth, due to its long isolation from other
continental landmasses. Its affinities are derived in part from
Gondwana, from which it
separated 82
MYA, some modest affinities with
New Caledonia and
Lord Howe Island, both of which are part of the same continental
plate as
New Zealand and in part from
Australia. More recently a component has been introduced by humans. New Zealand's
biodiversity exhibits high levels of
endemism, both in its
flora and
fauna. Until recently the islands had no native terrestrial
mammals except for
bats (although mammals did exist in New Zealand until 19 million years ago), the main component of the fauna being
insects and
birds. Its flora is dominated by Gondwanan plants, comprising historically of
forests, most famously the giant
kauri. New Zealand has developed a national
Biodiversity Action Plan to address conservation of considerable numbers of threatened flora and fauna within New Zealand.
Evolution of New Zealand's biodiversity
The break up of the
supercontinent of Gondwana left the resulting continents and microcontinents with shared biological affinities. New Zealand, along with New Caledonia, began to move away from
Antarctic Gondwana 100 MYA, the break being complete by 82 MYA. It has been moving northwards since then, changing both in relief and
climate. At some points it has been mostly underwater, with as little as 18% of the present surface area being above the water. Of the original biodiversity that it carried with it from Gondwana several groups remain: predominantly plants, such as the
podocarps and the
Southern beeches, but also a distinctive
insect fauna, New Zealand's unusual frogs and the
tuatara, as well as some of New Zealand's birds. It seems likely that some primitive mammals also were part of the original cargo.
The two sources of New Zealand's biodiversity following separation from Gondwana have been
speciation and air- or sea-borne immigration. Most of these immigrants have arrived from
Australia, and have provided the majority of New Zealand's
birds and
bats as well as some
plant species (carried on the wind or inside the guts of birds). Some of these immigrants arrived long enough ago that their affinities to their Australian ancestors are uncertain; for example, the affinities of the unusual
Short-tailed Bat were unknown until
fossils from the
Miocene were found in Australia. It has been suggested that the unusual
adzebills are related to the
Kagu of New Caledonia, and the ''
Cyanoramphus'' parakeets are thought to have originated in New Caledonia. The link between the two island groups also includes affinities between
skink and
gecko families.
Elements of New Zealand's Biodiversity
Floral biodiversity
The kauri of North Island were the tallest trees in New Zealand, but were extensively logged and are much less common today.
The history, climate and geology of New Zealand have created a great deal of diversity in New Zealand's vegetation types. The main two types of forest have been dominated by
podocarps and
southern beech. Podocarps (Podocarpaceae), an ancient
evergreen gymnosperm family of trees, have changed little in the last 190 million years. Forests dominated by podocarps form a closed canopy with an understory of
hardwoods and shrubs. The forests of southern beeches, from the genus ''Nothofagus'', comprise a less diverse habitat, with the beeches of four species dominating the canopy and allowing a single understory. In the north of New Zealand the podocarp forests were dominated by the ancient giant
kauri. These trees are amongst the largest in the world, holding the record for the greatest timber volume of any tree. The value of this was not lost on early
European settlers, and most of these trees were felled.
The remaining vegetation types in New Zealand are grassland of grass and
tussock, usually associated with the subalpine areas, and the low shrublands between grasslands and forests. These shrublands are dominated by
daisies, which can become woody and 3 m high.
Faunal diversity
Until 2006 it was thought that no mammals, other than bats and
marine mammals, had reached New Zealand before humans did. The discovery of a
femur and
mandibles of an extinct non-volant mammal in
Otago, dated at 16-19 million years old, has changed the view of New Zealand's evolutionary history, as it strongly suggests that mammals had been part of New Zealand's fauna since the break-up of Gondwana. The fossil has been called
SB mammal. It is not known when, or why, land mammals went extinct in New Zealand but there were none present on new Zealand for several million years before the arrival of man.
The Short-tailed Bat (from the monotypic family
Mystacinidae), having arrived in the late
Oligocene, has had plenty of time to
evolve, and has begun to fill the role of a small terrestrial mammal, flying out from roosts at night but frequently foraging on the ground. Some plants have evolved with the bats and are fertilised on the ground by the bats. The Long-tailed Bat (''
Chalinolobus tuberculatus''), a more recent arrival, is relatively common.
Birds comprise the most important part of New Zealand's
vertebrate fauna. It is uncertain if many birds in New Zealand are descended from Gondwanan stock, as
DNA evidence suggests that even the
ratites (the
kiwis and the
moa) arrived after the split from Antarctica. Recent studies suggest that
New Zealand wrens are Gondwanan descendants. DNA studies seem to indicate that the wrens are the most ancient of all
passerines, splitting from the ancestral passerine stock at the time New Zealand become an isolated land mass. In the absence of mammals, birds diversified into the
niches usually filled by mammals in other ecosystems.
The extinct
Huia was a member of the endemic family Callaeidae.
The
moa, of which there were 10 species, were large browsers, and were in turn the prey species of the giant
Harpagornis Eagle or Haast's Eagle. Both moa and
eagles became extinct shortly after the arrival of humans to New Zealand sometime around 1300 CE. It appears that human hunters exterminated the moa populations, which deprived the Harpagornis of their primary food source, leading to the extinction of that species, as well. New Zealand's emblematic
kiwi fills the role of a small forager of the leaf-litter, and the enigmatic
adzebill was a universal omnivore. The wattlebirds,
Callaeidae, are a family endemic to New Zealand, but many other New Zealand birds show clear affinities to Australia, including the
New Zealand Pigeon and the
New Zealand Falcon, as well as various
parrots,
rails,
waders,
owls, and
seabirds (albeit often with a New Zealand twist). Of the 245 species of birds from the greater New Zealand (the main islands along with the offshore islands, also including
Norfolk Island), 174 were endemic, roughly 71%. Of these, about 32% of the
genera were endemic.
The tuatara is a unique component of New Zealand's biodiversity and the only surviving genus in the order Sphenodontia.
No
agamas,
iguanas, land
turtles or snakes are recorded from New Zealand. The
fossil record shows one crocodile, possibly a
mekosuchine crocodile, in the
Miocene, but otherwise the only
reptiles to reach New Zealand were
skinks,
geckos, and the
tuatara, a
living fossil. The tuatara, reaching 60 cm, are New Zealand's largest reptiles.
Frogs, which because of their intolerance for
saltwater are assumed to have descended from ancestors that broke off from Gondwana, are one of the few exceptions to the rule that amphibians are never found on oceanic islands (another being the frogs of Fiji). New Zealand's few wholly freshwater fishes are derived from
diadromous species.
New Zealand's invertebrate community displays strong Gondwanan affinities, and has also diversified strongly, if unevenly. There are over a thousand species of
snail, and many species of insect have become large and in many cases flightless, especially
grasshoppers and
beetles. There are, however, less than 12 species of
ant. The most famous of New Zealand's insects, the
wetas, are ground-living relatives of the
crickets that often reach enormous proportions.
Endemism
New Zealand has a high number of endemic species:
★ 80% of all vascular plants
★ 70% of all native terrestrial and freshwater birds
★ All bats
★ All native amphibians
★ All reptiles
★ 90% of freshwater fish
Of New Zealand's estimated 20,000 fungi species, only about 4,500 are known. New Zealand also has two sub-species of endemic
cetaceans,
Hector's Dolphin and its close relative
Maui's Dolphin.
Human impact
The Common Brushtail Possum is one of the 33 mammals introduced to New Zealand by humans.
The arrival of humans in New Zealand has presented a challenge for the native species, causing the
extinction of several. This is predominantly because many species in New Zealand have evolved in the absence of mammalian predators for the last few million years (a situation known as ecological naivety), thus losing the responses needed to deal with such threats. Humans
brought with them to New Zealand (intentionally or otherwise) a host of attendant species, starting with the
Polynesian Rat, and now including
stoats,
weasels,
Black Rats,
Norway Rats,
Brushtailed Possums, and
feral cats and
dogs, as well as herbivores such as
deer and
tahr (a wild goat species from the
Himalayas), which detrimentally affect native vegetation.
The date of the first arrival of the
Māori in New Zealand is given as around 1300 CE, but some recent evidence suggests that
Polynesian travellers arrived earlier, as Polynesian Rats seemed to have arrived in 500 CE. Their arrival set off a first wave of extinctions, eliminating smaller defenseless ground nesting birds such as the
New Zealand Owlet-nightjar. A second wave of extinctions was triggered by the arrival of the Māori, who hunted many of the larger species, such as the moa, adzebill and several large ducks and geese, for food. The Harpagornis and
Eyles's Harrier are thought to have gone extinct due to the loss of their food source. A third wave of extinction began with the arrival of
European settlers, who brought with them numerous new mammal species, particularly the predatory domestic
cat, and initiated more habitat modification. In all, over 50% of New Zealand's bird species are considered extinct, along with a species of bat and several frogs, a freshwater
fish (the
New Zealand grayling), skinks and geckos; this is second only to
Hawaii in terms of proportion of species lost.
The Silvereye is one of several species of birds that have introduced themselves to New Zealand in the wake of humans.
In some instances, the extinction of New Zealand's native fauna has brought about a natural colonisation from
Australia. In the case of the
Silvereye, which colonised New Zealand in the
19th century, it had no relative in New Zealand's original fauna and is now restricted to newer man-made
niches. In the case of the
Black Swan (which was originally thought to have been introduced by humans but is now suspected to have self-introduced), the invading species re-occupied part of its former range (the extinct
New Zealand Swan is now believed to be a subspecies of the Black Swan). The arrival of the
Pukeko and the
Swamp Harrier is more interesting, mirroring the arrival of the same two species in the past, before they evolved into the
Takahe and the Eyles's Harrier. Once these specialised birds declined and (in the case of the harrier) went extinct, their niches were available and colonisation could occur again.
Management
Today New Zealand's species are amongst the most threatened in the world. The New Zealand government, through the
Department of Conservation, works aggressively to protect what remains of New Zealand's biological heritage. It has pioneered work on
island restoration where offshore islands are systematically cleared of introduced species such as goats, feral cats and rats. This then allows the re-introduction of native species that can hopefully flourish in the absence of non-native predators. The longest running project of this type is on
Cuvier Island[1], but other islands are also being used such as
Tiritiri Matangi and
Mangere Island.
Establishment of conservation areas is not restricted to islands however and several
ecological islands have been established on the New Zealand mainland which are isolated by the use of
pest-exclusion fences.
See also
★
Geological history of New Zealand
★
Invasive species in New Zealand
★
Landcare Research has biodiversity as one of its major research areas.
References
★ Ericson P, Christidis L, Cooper, A, Irestedt M, Jackson J, Johansson US, Norman JA., (2002) "A Gondwanan origin of passerine birds supported by DNA sequences of the endemic New Zealand wrens." ''Proc Biol Sci''. '269'(1488):235-41.
★ Worthy, Trevor H., & Holdaway, Richard N. (2002) ''The Lost World of the Moa'', Indiana University Press:Bloomington, ISBN 0-253-34034-9
★ Worthy TH, Tennyson AJ, Archer M, Musser AM, Hand SJ, Jones C, Douglas BJ, McNamara JA, Beck RM (2006) "
Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific." ''Proceedings of the National Academy of Sciences'' '103'; 19419-23
1. Cuvier Island restoration (from the Department of Conservation website)
External links
★
New Zealand Biodiversity - Government web site.
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