Flight of the Huia: Ecology and conservaton of New Zealand's Frogs, Reptiles, Birds and Mammals
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Flight of the Huia: Ecology and conservaton of New Zealand's Frogs, Reptiles, Birds and Mammals
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| ISBN-13: | 9781927145203 |
|---|---|
| Publisher: | Canterbury University Press |
| Publication date: | 01/11/2016 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 412 |
| File size: | 8 MB |
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Flight of the Huia
Ecology and Conservation of New Zealand's Frogs, Reptiles, Birds and Mammals
By Kerry-Jayne Wilson
Canterbury University Press
Copyright © 2004 Kerry-Jayne WilsonAll rights reserved.
ISBN: 978-1-927145-20-3
CHAPTER 1
New Zealand: archipelago and mini-continent
Taking into consideration the peculiarities of the flora and fauna of these islands, and the entire absence of fossil remains indicating a former connection with other continents, we are justified in concluding that, during the whole Tertiary period at least, if not for much longer New Zealand has maintained its isolation from all other extensive tracts of land.
– Alfred R. Wallace (1883)
In the bottom left-hand corner of the world's largest ocean lies a land once home to some most unusual animals and plants. These species were so unlike those elsewhere that Jared Diamond, the well-known American biologist and author of the book Guns, Germs and Steel, suggested that studying life in New Zealand was the closest he could come to researching on another planet. Imagine how our understanding of what is biologically possible would be enhanced by an experiment in evolution independent of life as we know it. We are unlikely to get any such opportunity, and certainly not in our lifetimes, so the best experiments in the independent evolution of life accessible to today's biologists are to be found on isolated islands such as New Zealand.
Most oceanic islands are geologically young or insufficiently isolated to prevent plants and animals colonising from larger land masses. Diamond identified four island groups that have been isolated for long enough to evolve dramatically different life forms, and are large enough not to be plagued with high natural extinction rates. These are Hawaii, New Caledonia, Madagascar and New Zealand. Of these, he suggests New Zealand is the most interesting. Hawaii is the smallest and youngest; New Caledonia is ancient but small; and Madagascar, while both ancient and large, is too close to Africa to prevent the influx of that continent's mammals.
Once part of the enormous southern continent known as Gondwana, New Zealand is large, remote, has been isolated from other land masses for 80 million years and lacks the mammals that are dominant elsewhere. At least 80 per cent of the species belonging to most non-marine animal and plant groups are endemic. Some of these species belong to families or orders that occur nowhere else, which illustrates how long they have been separated and how distant their relationships have become. Only other remote islands like Hawaii have a similar proportion of endemic species (Table 1.1).
New Zealand consists of two large islands surrounded by loosely clustered small to moderately large islands. Effectively it is both an archi-pelago and a very small continent. As an archipelago New Zealand is of particular interest because it includes smaller islands of two distinct types. There are numerous land-bridge islands lying close inshore that were connected to the main islands during glacial advances (such as Stewart and Kapiti Islands). Further offshore there are truly oceanic islands that have never had a mainland connection. They range from the subtropical Kermadec Islands to subantarctic Campbell Island, and have been colonised by a subset of species found on the mainland.
Since humans discovered New Zealand about 2000 years ago, and permanently colonised this Gondwanan liferaft almost 1200 years later, the natural environment has been greatly altered. Almost a half of the native non-marine birds are extinct, and about half of those that remain are threatened or endangered. Of the endangered or threatened birds listed by Birdlife International in 2000, 5.3 per cent are endemic to New Zealand. Considering the country does not have a long list to start with, this is a disproportionately high figure: there are 62 New Zealand species on the list, placing New Zealand eighth equal when counties are ranked this way. All the other countries in the top 25 are larger, and most are tropical nations with far greater species diversity. As well as losing so many species, New Zealand's ecosystems have been much altered in other ways, with many foreign species introduced and habitats fragmented. Other catastrophic changes are less obvious; for example, the loss of many pollinators and seed dispersers. The integrity of our unique ecosystems is under severe threat.
We can appreciate how different New Zealand is from the intensely studied northern hemisphere ecosystems by comparing our numbers of vertebrate animals with those of the British Isles, a similar-sized temperate archipelago (Figure 1.1). Not only are many New Zealand species endemic, but many belong to families or orders that are restricted to this country (see Chapter 3).
The foundations of ecology were developed in the European and North American temperate zones, and even today most of the world's ecologists and the headquarters of most environmental organisations are based in that part of the world. Conversely, most endemic birds, most endangered species and the ecosystems under most immediate threat are in the southern hemisphere or the tropics.
A foreign land
The first Polynesians who came to New Zealand found landscapes, plants and animals very different from those they had previously known. They must have been thrilled to discover a land mass much larger and with a far greater variety of animals than the small, scattered islands whence they came. Not only were there more kinds of animals, but a special bonus was the large, easily hunted, meaty birds. European settlers also found New Zealand to be a foreign land, but for different reasons. They probably expected something resembling their temperate island homeland, and indeed there were superficial similarities, but the ancient evergreen Antipodean forests and their animals were fundamentally different from the open, deciduous forests of Europe.
Initially, neither Polynesian nor European settlers had time to contemplate the strange land, plants and animals, because they were faced with the pressing needs of food and shelter. Just like colonists elsewhere in the world, Maori and Pakeha alike tried to adapt the land to their previous lifestyles, rather than they themselves adapting to the new land. The European settlers were especially assiduous, and it would take several generations for either group to evolve a conservation ethic reflecting the needs of the native animals of this land.
It was long believed that the Maori settlers were the first people to visit these islands. However, during the 1990s it was discovered that kiore (Polynesian rat) had been in New Zealand for about 2000 years, more than a thousand years longer than the earliest likely date of Maori settlement. They could not have arrived without human assistance, and appear in the subfossil record at about the same time on both main islands. We will probably never know just who those people were that brought the rodents here, as at that time kiore were present on most other South Pacific islands. In a land bereft of mammals, the small ground-dwelling birds and reptiles were defenceless against even this small rat, and we can picture a plague of kiore sweeping across the land with no pied piper to come to the rescue. By the time the Polynesians settled New Zealand around AD1200 (see Chapter 5), many of the small ground-dwelling birds, reptiles, frogs and invertebrates were already extinct.
When Europeans encountered New Zealand, the bird fauna, in particular the large meaty species such as the famous moa, had become further depleted by Maori. By the time of Captain Cook's brief visit in 1769, at least 40 species of bird had become extinct, along with three species of native frog. Many other birds and reptiles had also disappeared from large parts of their original range. Almost a third of the forests, mostly in the drier eastern parts of the main islands, had been destroyed (Figure 1.2). Many New Zealand birds had evolved to become giants of their kind, with reduced powers of flight, long lifespans and small clutches. Such an existence had served them well for millions of years but left them ill-prepared for the threats posed by rats and humans.
The first European visitors did not venture far from their ships but, like those unknown first people, they brought their own, larger rat that posed additional threats to native life forms. By 1800, explorers, sealers, whalers, missionaries and traders were regular visitors. Settlers began arriving early in the nineteenth century, and in 1839 the first of the planned British settlements was founded at what is today Wellington. Other settlers quickly followed. While the Polynesians and first Europeans had been largely hunters, the new colonists brought foreign seeds, animals and technology – and the will to carve out new British settlements in the Antipodes. The European arrival heralded an era of extra-ordinarily rapid and extensive habitat change. Between 1800 and 1950, 90 per cent of all wetlands and more than half the remaining forests were lost, and about 16 more bird species become extinct. Indigenous habitats were fragmented into small patches that subsequently became highly modified by introduced mammals. Numerous species of animals and some plants now survive only on predator-free offshore islands.
Why were so many of New Zealand's species so vulnerable to hunting and habitat change? To answer this question we need to understand their ancient origins, and that means going back into the depths of time, before New Zealand existed as such.
Break-up of Gondwana
During most of the Mesozoic the lands that make up the bulk of the southern hemisphere land masses, plus additional lands now located in the northern hemisphere, were united in the supercontinent Gondwana. On the eastern fringe of Gondwana, flanked by west Antarctica on one side and Australia on the other, lay the ancient proto-New Zealand land mass. During the Cretaceous, Gondwana gradually separated into smaller continents, eventually leaving what is today Antarctica centred on the South Pole, while offshoots became Africa, India, Madagascar, South America, Australia and New Zealand. The processes of plate tectonics and drifting continents are not well understood by many people, and an excellent explanation of this seemingly improbable process, with particular reference to New Zealand, is presented by Graeme Stevens in his 1985 and 1988 books Lands in Collision and Prehistoric New Zealand.
There has been land in the New Zealand region since mid-Jurassic times, about 160 million years ago, and at its peak size, 135 million years ago, the ancient land mass was almost half the size of present-day Australia and completely different in shape. It extended north to New Caledonia, west to the Lord Howe Rise, east to the Chatham Islands and south to the edge of the Campbell Plateau. At that time warm, temperate conditions prevailed over much of Gondwana, and the New Zealand region was virtually contiguous with what was to later become Australia and Antarctica.
Late in the Jurassic, Gondwana began to rift into the sectors that would eventually become today's continents. The initial split separated a larger western part (South America, Africa, Arabia, Madagascar and India) from a smaller eastern part, which included Antarctica, Australia, New Guinea, New Caledonia and New Zealand. The fragmentation of West Gondwana has little bearing on our story and can be summarised briefly. A rift opened between India/Madagascar and Africa, then in the late Cretaceous India separated from Antarctica and began to move northward, eventually to collide with what is now Asia. Next, Africa and South America pulled apart, then Africa separated from the remaining Gondwanan lands.
The history of East Gondwana is of much greater relevance to New Zealand. It remained a single continent long after the western part had split up. New Zealand and South America were still connected via Antarctica until about 85 million years ago, which explains the close affinities of some New Zealand and South American plants and animals; for example, southern beech trees and some freshwater insects and fishes. The presence of marsupials in both Australia and South America suggests that land connections between these two continents and Antarctica were not broken until the Eocene period, around 50 million years ago.
A rift between Australia and the greater New Zealand region formed much earlier, about 120 million years ago in the early Cretaceous, so the Tasman Sea began to form while both lands were still attached to Antarctica. During the mid- to late Cretaceous, the climate over much of Gondwana (including the New Zealand region) cooled but remained temperate as the Australasian part of Gondwana rotated southwards. The land links between the greater New Zealand region (including New Caledonia) and Gondwana eroded, and the land connections with Antarctica were finally severed 80–85 million years ago. At the end of the Cretaceous, the land mass destined to become New Zealand still lay close to the eastern edge of Australia, and it appears that the ancestors of the kiwi colonised New Zealand about this time or shortly there-after. The Tasman Sea continued to widen until it reached its present size about 60 million years ago.
New Zealand has drifted northwards throughout the Tertiary period. By the end of the Cretaceous, the greater New Zealand region, which still incorporated New Caledonia and the Chatham Islands, was smaller than it had been earlier in the Cretaceous, low-lying and partly covered by ocean. The last major land link to be severed was between eastern Antarctica and Australia, about 55 million years ago. Since this was one of the key events in shaping the New Zealand fauna, some knowledge of the flora and fauna of the Cretaceous age is necessary to understand subsequent events in New Zealand's ecological history.
New Zealand's Cretaceous flora and fauna
Reptiles were the dominant terrestrial vertebrates at the time New Zealand severed its land connections with Gondwana. The Cretaceous reptiles were a diverse and magnificent lot, including terrestrial dinosaurs, flying pterosaurs, marine ichthyosaurs and plesiosaurs. The Cretaceous was an especially interesting period for New Zealand to begin this experiment in evolutionary isolation. Soon the reptiles were to suffer mass extinction. Mammals had appeared on the scene a hundred million years before the demise of the dinosaurs, but despite many of the lineages having evolved, they were of little consequence and their major radiation took place after the demise of the ruling reptiles.
Unfortunately, our knowledge of New Zealand's Cretaceous vertebrates is fragmentary and few land animals of that time appear in the fossil record. Since that period New Zealand has undergone tectonic and volcanic upheavals that have destroyed or distorted most rocks that could contain Cretaceous fossils of terrestrial animals.
When New Zealand separated from Gondwana, it took along a selection of the animals and plants that lived during the reign of the dinosaurs. No New Zealand dinosaurs, pterosaurs or marine reptiles appear to have survived the Cretaceous/Tertiary mass extinction, but other species did and their descendants comprise an important element in the present-day biota. Modern plant and animal groups derived from ancestors that lived on the proto-New Zealand land mass during the Cretaceous include moa, New Zealand wrens, tuatara and native frogs; probably geckos, kauri, podocarps, weta, peripatus, the giant land snails and, possibly, skinks. Some of these species, including tuatara and native frogs, belong to primitive groups that have since become extinct in other parts of the world but soldiered on in New Zealand, isolated from other evolutionary pressures. New Zealand's beech, podocarp and kauri forests date back to the Cretaceous when these forest types covered much of Gond-wana. Today, southern beeches (Nothofagus) occur in New Zealand, the wetter, cooler parts of southern South America and eastern Australia, the montane forests of New Guinea and much of New Caledonia – all lands formerly part of Gondwana. Nothofagus fossils have also been found in Antarctica.
(Continues...)
Excerpted from Flight of the Huia by Kerry-Jayne Wilson. Copyright © 2004 Kerry-Jayne Wilson. Excerpted by permission of Canterbury University Press.
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Table of Contents
Contents
Title Page,Preface,
Acknowledgements,
1: New Zealand: archipelago and mini-continent,
2: New Zealand's frogs and reptiles,
3: Ecology of birds and bats,
4: Vertebrates in pre-human New Zealand,
5: Extinctions of New Zealand vertebrates,
6: Acclimatisation,
7: The forest vertebrate community in the twentieth century,
8: Seabirds and marine mammals,
9: Conservation,
10: Seeking solutions,
Appendices,
Notes,
References,
Index,
Plates,
Copyright,