Biodiversity of New Zealand Most Unusual on Earth

New Zealand has extraordinary flora and fauna, descended from Gondwanan wildlife or since arriving by flight, swimming or being carried across the sea.About 80% of the flora in New Zealand occurs only in New Zealand, including more than 40 endemic genera.The two main types of forest are those dominated by podocarps and/or the giant kauri, and in cooler climates the southern beech. The remaining vegetation types in New Zealand are grasslands of tussock and other grasses, usually in sub-alpine areas, and the low shrub lands between grasslands and forests.

Until the arrival of humans, 80% of the land was forested. Until 2006, it was thought, barring three species of bat (one now extinct), there were no non-marine native mammals. However, in 2006, scientists discovered bones that belonged to a long-extinct, unique, mouse-sized land animal in the Otago region of the South Island. New Zealand’s forests were inhabited by a diverse range of megafauna, including the flightless moas (now extinct), four species of kiwi, the kakapo and the takahe, all endangered by human actions. Unique birds capable of flight included the Haast’s eagle, which was the world’s largest bird of prey (now extinct), and the large kaka and kea parrots. Reptiles present in New Zealand include skinks, geckos and living fossil tuatara. There are four endemic species of primitive frogs. There are no snakes and there is only one venomous spider, the katipo, which is rare and restricted to coastal regions. However, there are many endemic species of insects, including the weta, one species of which may grow as large as a house mouse and is the heaviest insect in the world.

Due to its long isolation and the unique prominence of avifauna in ecological niches occupied elsewhere by other species, New Zealand has suffered a high rate of extinctions, including the moa species, the huia, laughing owl and flightless wrens (which formerly occupied the roles elsewhere occupied by mice). This is due to human activities such as hunting and pressure from introduced feral animals, such as weasels, stoats, cats, goats, deer and brushtailed possums.

However, New Zealand has led the world in island restoration projects where offshore islands are cleared of introduced mammalian pests and native species are reintroduced. Several islands located near to the three main islands are wildlife reserves where common pests such as possums and rodents have been eradicated to allow the reintroduction of endangered species to the islands. A more recent development is the mainland ecological island.

Floral biodiversity

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 fertilized 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 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.

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.

Human impact

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.

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, 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.

Source:en.wikipedia.org

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