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EVOLUTION OF NEW ZEALAND'S BIODIVERSITY The break up of the and the Southern Beech es, but also a distinctive Insect fauna, New Zealand's unusual frogs and the Tuatara , as well as some of New Zealand's birds. 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 Bird s, Bat s and 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 Fossil s from the Miocene were found in Australia. It has been suggested that the unusual Adzebill s is related to the Kagu of 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 history, climate and geology of New Zealand has created a great deal of diversity in New Zealand's vegetation types. The main two types of forest have been dominated by Podocarp s 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 Hardwood s 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 Europe an settlers, and most of these trees were felled. The remaining vegetation types in New Zealand are grassland of grass and Tussock , usually associated withe the subalpine areas, and the low shrublands between grasslands and forests. These shrublands are dominated by Daisies , which can become woody and 3m high. Faunal diversity No mammals, other than bats and Marine Mammal s, reached New Zealand before humans did. 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'') 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 Ratite s (the Kiwi s and the Moa ) arrived after the split from Antarctica. Recent studies suggest that New Zealand Wren s 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 Niche s usually filled by mammals in other ecosystems. The Moa , of which there were 10 species, were large browsers, which were in turn the prey species of a giant Eagle , the Harpagornis or Haast's Eagle. Both moa and eagles became extinct shortly after the arrival of humans on 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 , the New Zealand Falcon , as well as various Parrot s, Rail s, Wader s, Owl s, and Seabird s, 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 Agama s, Iguana s, land Turtle s or snakes ever reached New Zealand. The Fossil Record shows one crocodile, possibly a Mekosuchine Crocodile , in the Miocene , but otherwise the only Reptile s to reach New Zealand were Skink s and Gecko s, along with the Living Fossil , the Tuatara . The tuatara, reaching 60 cm, are New Zealand's largest reptile. Frog s, which because of their intolerance for Saltwater must have been descended from ancestors that broke off from Gondwana, are the exception to the rule that amphibians are never found on oceanic islands. New Zealand's few wholly freshwater fishes derive from marine ancestors. 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 Grasshopper s and Beetle s. There are, however, less than 12 species of Ant . The most famous of New Zealand's insects, the Weta s, are ground-living relatives of the Cricket s that often reach enormous proportions. ENDEMISM New Zealand has a high number of endemic species:
Of New Zealand's estimated 20,000 fungi species, only about 4,500 are known. New Zealand also has an endemic Cetacea n, the Hector's Dolphin . Some orders and families are completely endemic to New Zealand. NEW ZEALAND'S BIODIVERSITY AND HUMANS The arrival of humans in New Zealand has presented a challenge for the native species that has caused the Extinction of many species. This due predominantly to the species of New Zealand having evolved in the absence of mammalian predators, be they human or otherwise (a situation known as ecological naivety), since they have never evolved or have lost the responses needed to deal with the threats. As humans arrived they Brought With Them , intentionally or otherwise, a host of other attendant species, starting with the Polynesian Rat , but now including Stoat s, Weasel s, Black Rat s, Norway Rat s, Brushtailed Possum s, Feral Cat s and Dog s, as well as herbivores such as Deer and Tahr (a wild goat species from the Himalaya s), which detrimentally affect native vegetation. The date of the first arrival of the Māori in New Zealand is given as around 1300 AD, but some recent evidence suggests that some Polynesia n travellers arrived earlier, as Polynesian Rats seemed to have arrived in 500 AD. Their arrival set off a first wave of extinctions, eliminating smaller defenseless ground nesting birds. 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, for food. The Harpagornis presumably went extinct because of the loss of its food source. A third wave of extinction began with the arrival of Europe an 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, ''Prototroctes oxyrhynchus''), skinks and geckos; this is second only to Hawaii in terms of proportion of species lost. One interesting phenomenon following the extinction of New Zealand's native fauna is the natural colonisation that has occurred from Australia since the arrival of humans. In the case of the Silvereye , which colonised New Zealand in the 19th Century , there was never a relative of the invader in New Zealand's original fauna, and they are restricted to newer man made Niche s. In the case of the Black Swan , (which was originally thought to have been introduced but is now suspected to have self introduced itself as well) it was the re-occupation of 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, as they mirror 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. 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 the use of offshore reserves, cleared of introduced species, as safe places for New Zealand's threatened species. SEE ALSO
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