Publications
Acknowledgments
Introduction
Executive summary
2 National elements of significance - an overview
3.2 Fauna - significant features
3.4 Some special terrestrial areas
4.2 Some special wetland areas
6 Biodiversity of Australia's external territories
This paper was principally prepared by Josephine Mummery and Neal Hardy of the Biodiversity Unit within the Commonwealth Department of the Environment, Sport and Territories (DEST). Input from other members of the Biodiversity Unit and the DEST Portfolio is acknowledged, as is that from the Biological Diversity Advisory Committee.
This paper has been refereed by Mr Graeme Beach; Ms Pam Beesley; Dr John Benzie; Mr John Briggs; Dr John Clarkson; Dr Hal Cogger; Professor Jack Elix; Dr Malcolm Gill; Mr Roger Good; Dr Penny Greenslade; Dr Surrey Jacobs; Dr Peter Kershaw; Professor Jamie Kirkpatrick; Dr John Kuo; Dr Sam Lake; Dr Byron Lamont; Dr Peter Last; Dr John Paxton; Dr Winston Ponder; Dr Jim Puckridge; Dr Pat Quilty; Professor Barry Richardson; Dr Craig Sanderson; Dr Richard Schodde; Dr Ron Strahan; Dr Leon Zann
Note on taxonomy
The taxonomic system used by zoologists and botanists to classify organisms is hierarchical. The only taxonomic unit (taxon; plural taxa) that actually exists in nature is the species, generally identified by reproductive isolation from other species. Species that are very similar are placed in the same genus. Similar genera are then placed in the same family and families are grouped into orders and classes. Above this the classification is subphylum and phylum (plural phyla) for animals, and division for plants. For example:
BOTANY
Division - Magnoliophyta
Class - Dicotyledonae
Order - Myrtales
Family - Myrtaceae
Genus - Eucalyptus
Species - Eucalyptus regnans
ZOOLOGY
Phylum - Arthropoda
Class - Insecta
Order - Hymenoptera
Family - Formicidae
Genus - Nothomyrmecia
Species - Nothomyrmecia macrops
The variety of life in Australia has long been recognised as distinctive and globally significant. Many highly regarded and cutting-edge texts have been written on components of Australia's biodiversity, or on major biotic groups. Few attempts, however, have been made to document an overview of why Australia's biodiversity is significant, nationally or globally.
This paper provides a picture of some of the immense variety of living organisms that inhabit this continent, and shows how this diversity is significant. A brief overview of the evolutionary development of Australia's biodiversity is first provided as this sets the scene for understanding its distinctiveness. Significant features of the biodiversity of terrestrial, inland aquatic, and marine environments are then explored, followed by those of Australia's external territories. In particular, the highly endemic nature and richness of Australia's biodiversity is outlined, and the many ancient origins and specifc adaptations to Australian environments are documented. A number of areas in Australia of particular significance for their biodiversity are then briefly described.
Given the scope and purpose of the paper, it has been necessary to concisely and very briefly summarise much of the available information, and it has not been possible to include all relevant material. Nevertheless, many sources have been used, including the most up-to-date opinions of specialists in the area, and the reference list provides a guide to those seeking further information.
The paper is organised into two information streams. The executive summary together with the highlighted boxes at the beginning of each major section provide a non-technical overview or summary of the paper. The other stream is the more technical text which can be read sequentially, in sections, or accessed through the index. Technical terms used in the paper are explained in a detailed glossary.
Australia has a rich and distinctive flora and fauna. The major reason for this is related to the history of the Australian landmass. The world's continents were once all joined in a single landmass called Pangaea. In the Jurassic period (about 160 million years ago) a northern continent, Laurasia, and a southern continent, Gondwana, split apart. Gondwana fragmented gradually over geological time, with India and then New Zealand moving away from the Australia-Antarctica-South America group during the Cretaceous period (140 million years ago). The latter group of continents separated from each other during the Tertiary period (from about 70 million years ago). By about 40 million years ago, Australia was fully separated from Antarctica and commencing a northward drift as an isolated continent.
At the time of Australia's break from Antarctica, there were both marsupial and placental mammals on the continent but, apart from bats, placentals subsequently died out. Marsupials radiated widely and became adapted to the increasing aridity caused by climatic changes during Australia's northward movement. The characteristic Australian flora, including eucalypts, acacias, casuarinas, spinifex, grasstrees and banksias, also diversified during this time. As Australia moved closer to the Asian landmasses, invasions and colonisations from its northern waters were common, including many mangroves, corals, lizards, snakes, placental mammals, birds, scorpions and insects.
Despite this long history, the last 200 years have seen the most dramatic changes to Australia's biological diversity. Following European settlement many ecosystems were radically simplified and fragmented, and a suite of exotic plants and animals was introduced. Associated large-scale disruption of indigenous societies has meant that in many cases the traditional knowledge of Australian flora and fauna has been permanently lost.
Australia's long isolation has resulted in a flora and fauna that is both highly endemic and has great species richness compared to many other parts of the world. Endemic groups are those that are unique to a region and Australia has both a large number of endemic species, and a high proportion of endemic species in particular groups. For example 85 per cent of vascular plant species and 82 per cent of mammal species, excluding whales, are endemic to Australia. Species richness refers to the number of species in a particular area and is very high in Australia, especially in some notable areas such as the Queensland rainforests, the Great Barrier Reef and the South West Botanical Province of Western Australia.
Much of Australia's biota has an exceptionally long history. Stromatolites, such as those at Shark Bay, Western Australia, are formed by microbial mats of cyanobacteria (blue-green algae) and other microorganisms. Stromatolites date back 3500 million years in the Australian fossil record, and are thought to have been made by organisms which were among the first on earth. Many other organisms found in Australia today can be linked through the fossil record to ancient ancestors in existence during the continental shifts of the Pangaean and Gondwanan times. Indeed some modern species, surviving in isolated or specialised habitats, have changed little over time (relict species) and represent links to various stages in the history of Australia's biodiversity.
Because of the particular climatic and environmental features of the Australian continent some unique combinations of adaptive features have evolved. These include adaptations to arid conditions, variable water levels, fire and high salinity.
Australia's large span of latitude, with a variety of climatic zones from the tropical north to the cool temperate south, has allowed the development of a rich and diverse flora and fauna on land, in wetlands, and in the surrounding seas. Australia's external territories also contain endemic and unusual plants and animals.
Australia has a vast array of vascular plants most of which are unique, and more endemic families of flowering plants than any other country. Acacias and eucalypts have adapted to almost every habitat and dominate the landscape while the family Proteaceae is more diverse in Australia than elsewhere with 42 genera from a world total of 72. Of these, 35 are endemic to Australia (including banksias, grevilleas, hakeas, macadamias and waratahs). The more primitive seed-bearing plants are represented by the cycads (palm-like cone bearing trees) and a number of conifers, for example the huon pine and kauri pines.
Much of the Australian continent is dry, and many native Australian plants are uniquely adapted to survive harsh conditions. Sclerophylly is an adaptation to arid conditions in which the leaves are rigid and have a thick waxy cuticle. It is found in many plant groups, such as some acacias, eucalypts and banksias. Adaptation to fire is also common and some Australian plants require fire for regeneration.
On land there is an enormous diversity of mammals, birds, reptiles, frogs and invertebrates. All three major groups of modern mammals (monotremes, marsupials and placentals) co-exist in Australia and of the three species of egg-laying mammals (monotremes) known worldwide, two occur here (the platypus and echidna). The marsupials are the most common mammals in Australia with about 141 species, the majority of which are endemic.
Nearly half of Australia's birds, and most reptiles and amphibians are endemic and many groups of these animals are highly diverse compared to other continents. For example parrots are more varied in Australia than elsewhere in the southern hemisphere, and about 93 per cent of Australian frogs and 89 per cent of reptiles are found only here. The arid zones have an exceptionally large number of lizard species compared to similar habitats on other continents. Australia also has a huge invertebrate fauna with an estimated 140 000 species, many of which await discovery. The insects are extremely diverse and some families and most species occur only in Australia. With some 4000 species, ants are particularly diverse compared to the rest of the world, and form a vital part of many arid ecosystems.
Numerous interesting and highly specialised interactions have 'co-evolved' between organisms in Australia as part of their adaptation to the environment and to maximise use of resources. Seed dispersal, pollination and protection from predators are common themes of such interactions and these arrangements are often mutually beneficial to the organisms involved. Ants, which disperse seeds for numerous plants, are involved in a complex web of feeding and predation interactions, especially in arid areas.
The fauna of inland waterways and wetlands is varied and includes the well-known Australian inhabitant, the platypus, and two species of crocodiles: the endemic freshwater crocodile; and the more widely distributed saltwater crocodile. The waterways support a diverse invertebrate fauna much of which is endemic, including freshwater sponges, snails, shrimps, crayfish, isopods and many species of insects. Some faunal groups, such as freshwater mussels, crayfish and southern frogs, are particularly diverse in Australian waterways compared to elsewhere. Other groups that are common elsewhere, however, are either absent or have relatively few representatives here, including some insect, frog and bird families. Freshwater fish species are relatively few but include some endemic families. However, some fish, such as southern trouts, which occur all over the southern hemisphere, are most abundant and diverse in Australia. The inland aquatic flora is not as distinctive and, although some endemic species are found, most species are widely distributed.
Only a limited number of organisms in the world have adapted to life in salt lakes and Australia has many notable examples, including a number of endemic shrimps and gastropods. Many organisms have also evolved adaptations to cope with periods of drought, for example drought-resistant eggs or larvae; burrowing; and life-cycle adaptations including opportunist breeding after flooding.
Australia's seas support one of the richest fish faunas in the world. This is strongly regional, with a northern tropical zone; eastern and western warm temperate zones; and a southern cool temperate zone. The northern tropical zone has most species diversity but the majority of species are also distributed widely in the Indian and Western Pacific Oceans. The temperate zones have less species diversity but a majority of the species are endemic. Some fish families are uniquely diverse in Australian waters, for example pipefishes and seahorses, leatherjackets and anglerfishes, and there is an extremely rich fauna of sharks and rays. A number of marine species that are not endemic to Australia find security in Australian waters and are found here in greater numbers than in other parts of their range, for example a number of turtle species and the dugong.
Australia's external territories, including the Australian Antarctic Territory, Christmas Island, Norfolk Island and other offshore islands, have highly diverse and endemic marine communities. The islands also provide some important breeding sites for seabirds and seals. Christmas Island is the only known nesting site in the world for the rare but far-ranging Abbott's booby.
Australia's flora and fauna are well represented in the fossil record. Fossils of kauri pines and cycads have been found in 175 million-year-old fossil fish beds in New South Wales, indicative of their ancestral origins when all the continents were joined before 160 million years ago. Other plant groups (for example the family Proteaceae, southern beeches, acacias and many rainforest species) can be traced to a time when the southern landmass of Gondwana had split from Pangaea.
Some existing invertebrate species, such as the velvet worms, are relict species, having remained relatively unchanged for hundreds of millions of years. Several other invertebrate groups also have Pangaean origins while other faunal groups have fossil records extending back to Gondwanan times. These include the emu and cassowary, the parrots, and some turtles, geckos, frogs and invertebrates.
The Australian aquatic fauna provides several examples of animals with ancient origins. Crocodiles have a fossil ancestors record dating back over 200 million years and the Queensland lungfish is among the most ancient of living bony fishes with a fossil ancestry dating back over 400 million years. A number of fish families including the barramundi and salamanderfish have Gondwanan or Pangaean ancestry as do numerous aquatic invertebrate groups.
Many ancient marine animals live on the southern marine platform of Australia, which has been relatively stable for some 40 million years and the direct ancestral lineage of many invertebrate species found there today can be traced in the deposits to ancient times.
The overall biodiversity of a region is related to the variety of habitats and biological communities that have developed there. In this context Australia has a number of areas and specialised habitats that warrant special mention. The rainforests of north Queensland, the South West Botanical Province of Western Australia and the alps of southeast Australia form diverse assemblages of terrestrial habitats that are important for the extremely rich and endemic biotic communities that they support. The rainforests contain one of the highest concentrations of primitive plants in the world and harbour important links in the history of plant evolution.
The flora and fauna of Australia's inland waters have had to adapt to unpredictable rainfall, seasonal variation in evaporation rates, and high levels of salinity. Overall there is a scarcity of aquatic habitats, particularly in the arid and semi-arid areas. Despite this, Australia has a variety of wetland habitats provided by areas such as the Kakadu wetlands area in northern Australia and the lower Cooper wetlands, including the Coongie Lakes, in the centre. These wetlands include diverse habitats that vary in the wet-dry cycle, and the flora and fauna inhabiting them are notable for both their diversity and the large fluctuations of abundance that can occur.
The gorges and caves of central Australia, the coastal mangroves, the granite outcrops of the southwest of the continent and the mound springs of the Great Artesian Basin all represent specialised habitats where plants and animals have developed unique characteristics and adaptations.
Australia has a number of special marine habitats that are worthy of particular mention. The most well-known and spectacular of these is the Great Barrier Reef, which covers 350 000 square kilometres off the tropical northeastern coastline and has an incredibly rich biodiversity associated with coral reefs and islands.
The giant kelp forests of Tasmania and Victoria and the seagrass meadows found in many of our coastal waters provide important habitats for many marine species. Western Australian seagrass meadows, which collectively cover as much area as all the rainforests of Australia, are the most diverse in the world. The 'forests' and 'meadows' are home to many invertebrates and fish, and provide nurseries for many of their young.
Overall, Australia is an island continent that, due to its long geological isolation and special climatic features, is home to an enormous variety of uniquely evolved plants and animals. An exceptionally high proportion of these are only found in Australia, although a common ancestry with 'counterparts' in other regions can often be traced back to ancient times. For some groups of plants and animals the number of species (species richness) is outstanding and for many others the numbers are relatively high compared to most other parts of the world. These factors combine to make Australia's biological 'ark' globally significant in any terms.
This executive summary can be used with summaries of each major section to provide a non-technical overview of the paper. The section summaries are printed on a blue background and can be found at pages (18), (24), (31), (34), (45), (50), (58).
By any criteria, Australia's biodiversity differs from that of the rest of the world. Australia has many odd and different creatures, and to understand how they came to be here, and nowhere else, it is necessary to look into the past. The major reason for Australia's distinctive biodiversity is that for most of its history Australia has either been at the end of a chain of linked continents or widely separated from others. During that time of wide separation, Australia became a natural laboratory isolated from the rest of the world. As a result, while all continents except Australia (and Antarctica) share long records of, for example, primates, cats and bovids (cattle, sheep and goats), only Australia has the platypus, the koala and wombats.
Another feature of the Australian continent that distinguishes it from most other lands is its geological stability. Today, the Australian landmass lacks some of the features that characterise large portions of other continents, such as active mountains (including volcanoes), great rift systems, and great permanent lakes. During the last 300 million years, all these features have been active or present at some time, but a significant part of the continent has been geologically stable. Accordingly, and in contrast to other continents, vast areas have been subject over a long period to relatively low rates of topographical change.
Geological evidence indicates that, prior to 160 million years ago, all the continents were aggregated as the single landmass of Pangaea. While the distribution patterns for many biotic groups have been erased by extinction or subsequent radiation, scientists have been able to identify a number of components of the Australian biota that have remained relatively unchanged since Pangaean times. Surviving examples of these, which typically possess primitive features and are found throughout the world - but with a disjunct distribution - include several invertebrate, microbial and plant taxa.
ERA PERIOD EPOCH APPROXIMATE BEGINNING
(millions of years ago)
Cainozoic Quaternary Holocene (Recent) 0.01
Pleistocene 1.6
Tertiary Pliocene 5
Miocene 25
Oligocene 35
Eocene 60
Palaeocene 65
Mesozoic Cretaceous 145
Jurassic 210
Triassic 245
Palaeozoic Permian 285
Carboniferous 360
Devonian 400
Silurian 440
Ordovician 500
Cambrian 600
Precambrian 4500
Source: adapted from Kukalová-Peck 1991
By the middle of the Jurassic period, 160 million years ago, Pangaea was partly divided into the northern supercontinent Laurasia, and its southern counterpart, Gondwana. Gondwana remained intact until the early Cretaceous, some 140 million years ago. At that time Australia was broadly in contact with Antarctica, India and New Zealand and indirectly with South America and Africa, and biotic affinities between these landmasses are clearly evident. Gondwana fragmented over an extended geological period with India, Africa and then New Zealand moving away from the Australia-Antarctica-South America group during the Cretaceous period and the latter group of continents separating from each other within the Tertiary period (see Figure 1).
Figure 1: About 200 million years ago, the world's continents were aggregated in one landmass, Pandgaea. Over a period of many millions of years, Pangaea fragmented into two supercontinents, northern Laurasia, and southern Gondwana. These in turn became the continents as we know them today. The black dots indicate the approximate positions of the South Pole.
Australia started to separate from Antarctica about 53 million years ago and remained connected via Tasmania and the South Tasman Rise until about 38 million years ago. For more than 20 million years, Australia moved northwards in relative isolation through 30 degrees of latitude. This movement, with the progressive development of the present intense atmospheric circulation pattern, brought about massive climatic changes in the southern hemisphere. Rainforests became geographically more variable with an increase in drier communities, and were progressively replaced from the centre towards the margins of the continent by more open-canopied vegetation types. Sclerophylly, which originally developed in response to the low nutrient status of soils within the early rainforest vegetation, pre-adapted plants to survival and diversification under increasingly arid conditions, leading to the characteristically 'Australian' flora that includes eucalypts, acacias, casuarinas, spinifex, grasstrees and banksias. While aridity generally increased, there were several climatic fluctuations, with warm and moist conditions alternating with drier and cooler phases, and a progressive trend towards a more arid environment.
As well as the diversification of Australia's flora during this period, there was also considerable faunal adaptive radiation. Of particular significance is the fact that at the time of Australia's break from Antarctica, there were both marsupial and placental mammals on the continent (Godthelp et al 1992) but apart from bats, placentals subsequently died out (P. Kershaw 1993, pers comm). As Australia underwent the climatic changes outlined above, its marsupial fauna underwent a major radiation into a variety of habitats and many became adapted to drier regions by, for example, the production of highly concentrated urine and the ability to live without access to free water (Strahan 1988; R. Strahan 1993, pers comm1). Some invertebrate groups, such as the ant genus Melophorus, the termites Drepanotermes, and the collembolans Folsomides and Corynephoria, have adapted particularly well to the arid zone and may have radiated there (P. Greenslade 1993, pers comm).
1The organisations of personal communication contributors are shown at the end of the references section.
As Australia's top quarter drifted north of the tropic of Capricorn into the tropics, new lifeforms colonised its northern waters. Many tropical species of mangrove and coral joined Australia's biota as the northern waters warmed. Contact with the Sunda Arc occurred about ten million years ago but over a period of millenia, and opportunities for invasion increased as the landmasses drew closer. Eventually, when the Australian tectonic plate made contact with that of Asia, Australia was more easily invaded by terrestrial fauna. Examples of the Asian Tertiary invaders include many families of lizards and snakes, placental mammals such as the conilurine rodents, many birds, scorpions of the families Scorpionidae and Buthidae and many insects (Heatwole 1987).
While invasions and colonisations are often chance events and relatively rare, many of the taxa which entered Australia during this time nevertheless invaded several times. Dung beetles of the cosmopolitan genus Onthophagus may have invaded as many as 34 times (Matthews 1972). Some of the taxa spread throughout the continent and underwent extensive adaptive radiation.
In most cases these recent invaders have scarcely diverged from their Asian relatives and where there is divergence it is usually at the species or subspecies level. Examples include the wood frog, Rana daemeli, native rats and the rainbow bee eater, Merops ornatus (Heatwole 1987).
Plant genera that most probably entered Australia by this route include those of the primitive families Annonaceae, Hernandiaceae and Myristicaceae and the two species of Ericaceae, Agapetes meiniana and Rhododendron lochae (Beadle 1981). However, accumulated fossil evidence has demonstrated that there was no massive invasion of rainforest plants from Southeast Asia into Australia as had been traditionally accepted (Truswell et al. 1987).
The invasions outlined above form the most recent component of a continuum of invasions from Asia and elsewhere and may be taken as post-Tertiary, that is, from about 1.6 million years ago. Since the late Tertiary, Australia has been subject to the dramatic climatic fluctuations associated with global glacial-interglacial cycles. Fire, which has always been a component of the Australian sclerophyll vegetation environment, also became more prevalent. The combined impact of these factors resulted in a marked expansion of open sclerophyll forest and woodlands and, during cool dry glacial periods, the development of extensive steppe grassland and herbfields in southern Australia. Rainforest and other fire sensitive communities became largely restricted to isolated wetter east coast areas and to fire-free stream valleys and rocky outcrops (Kershaw 1988). These trends accelerated because of the burning activities of Aboriginal inhabitants after their arrival at least 50 000 years ago (Roberts et al. 1990). The character of the woodland changed particularly; it became more open and grasslands spread further.
It is also probable that Aboriginal people were involved in the massive phase of megafaunal extinction within the late Pleistocene. There had been a trend towards increased body size of Australian marsupials through the Tertiary and Quaternary periods, culminating in the late Pleistocene, which witnessed the extinction of almost all the large marsupials - some 40 species (Martin 1984). This loss of a substantial grazing and browsing component would in itself have resulted in major changes to the entire Australian environment.
In the last 200 years, however, the most dramatic change to Australia's biological diversity has occurred in the shortest period of time. After European settlement, many ecosystems were radically simplified and fragmented, a suite of exotic species was introduced, and many native species were displaced or became extinct. The associated large-scale disruption of indigenous societies has meant that in many cases traditional knowledge of, and interactions with, Australian flora and fauna, such as burning regimes, have been permanently lost or altered.
As a result of the evolutionary process, the Australian flora and fauna is distinct in many ways from that found elsewhere. Long isolation has led to the evolution of many animals and plants found only in Australia (i.e. endemic species) and its stability has allowed the survival of many ancient and relict species. Also Australia's climate and landscape variability have fostered the development of a biota with many adaptations to local conditions - and these species have interacted in unique ways, to form diverse communities. These conditions have allowed the evolution of several highly speciose groups, such as eucalypts and ants.
Although many endemic genera and species are to be expected on a large island continent, levels of endemism in Australia are notably high. Compared with other countries, Australia not only has a large number of endemic species, but these also form a high percentage of the total (WCMC 1992; see Figure 2). From what is presently known, 85 per cent of flowering plant species (ESDWGBD 1991), about 82 per cent of mammal species excluding whales (Strahan 1988; Eldridge and Close 1992; G. Richards 1993, pers comm; R. Strahan 1993 and 1994, pers comm) and 89 per cent of reptile species are endemic to Australia (Cogger 1992).
While endemic species and genera are remarkable from a biological point of view, endemic families are even more important. It is of great significance, therefore, that endemism occurs at the taxonomic level of family in Australia, with six mammal, about four bird, eight fish, and 14 families of flowering plants endemic to Australia as well as numerous families of invertebrates (R. Strahan 1993, pers comm; R. Schodde 1993, pers. comm.; Paxton et al. 1989; Beadle 1981, B. Briggs 1994, pers. comm.).
Figure 2: On a scale, Australia has a very high proportion of endemic species. Source: WCMC 1992
Australia's plants and animals are among the most diverse in the world and some areas have globally outstanding species richness, such as the Great Barrier Reef, the rainforests of north Queensland and the South West Botanical Province of Western Australia.
Also, it is found that when Australian groups of plants and animals are compared with their counterparts in the rest of the world, several are notable for the numbers of species they include. For instance, Australia has many vascular plant species, and is particularly well known for its orchids. In addition, it is one of the most lichen-rich countries in the world (Rogers 1992; WCMC 1992). Marsupials are diverse and numerically abundant and Australia's reptile fauna is also significantly large. Several invertebrate groups also contain many species. For example the ant and cockroach faunas comprise 15 per cent and 12 per cent of the global faunas respectively (Naumann et al. 1991; WCMC 1992).
The geological stability of the Australian landmass has resulted in the ability to trace the origins of some organisms living in Australia today back to extremely ancient times. For example, Australia has outstanding examples of stromatolites, structures formed by microbial mats of cyanobacteria (blue-green algae) and other microorganisms. The oldest known stromatolites are about 3500 million-year-old fossils and were discovered near the mining centre of North Pole in the Pilbara, Western Australia. Actively growing stromatolites can be found at Shark Bay, Western Australia, where one type of cyanobacterium, widespread in the microbial mats, is thought to be a direct descendant of forms that flourished 1900 million years ago. It represents one of the longest continual biological lineages known (Burne 1991-92).
Australia has many examples of lineages that have survived since Pangaean and Gondwanan times. These often provide a living history of the groups to which they belong, and give clues to the evolution of many other extant (that is, still existing) species and groups. Such animals and plants, which can be seen as 'living fossils', are evidence of our past biotic links with other continents and countries and give vital information on past climates. By increasing our understanding of evolutionary processes, they also help us to identify groups and regions important for contemporary evolutionary change.
The ancient lineages of many groups are reflected in their current distributions. Organisms that are of Pangaean origin typically possess primitive features and have a globally disjunct distribution as noted in Section 1. Many extant plants and animals with Gondwanan origins have distributions reflecting their centres of origin and the state of fragmentation of the Gondwanan landmass. The ratite birds, which include the emu and ostrich, are believed to have Gondwanan origins as they are found on most southern continents, including Africa, Australia and South America (Schodde and Tidemann 1986). Acacias and the Proteaceae are also probably of Gondwanan origin, with a wide distribution on southern continents occurring (mainly) in India, Africa, Madagascar, Australasia and South America (White 1986). Species of Nothofagus (southern beeches) however, are absent from Africa (White 1986), and fossils of this genus have never been found there (P. Kershaw 1994, pers comm). The less cosmopolitan distribution of Nothofagus indicates that it may have evolved later, as Gondwana was fragmenting.
A further distinction can be made between extant organisms with links to ancient ancestors and those that have remained relatively unchanged from a previous age, often in biogeographically isolated areas (i.e. relict species). Examples include the blind trapdoor spider Troglodiplura lowryi from caves in the Nullarbor Plain and the conifer Microstrobos fitzgeraldii which is found at a few sites in the Blue Mountains (NSW). The only other member of the Microstrobos genus is found in Tasmania. The palm Livistona mariae, another relict species, occurs in gorges in the Macdonnell Ranges in the Northern Territory, and is a survivor of times when moist conditions prevailed more generally (Flannery and Rodd 1988).
Adaptations to Australian environments have often occurred over long periods and adaptive radiations have resulted in surviving species often being distinctive. The platypus (Ornithorhynchus anatinus) is perhaps the most well known example, but is joined by other species such as the marsupial moles (Notoryctes typhlops and N. caurinus), the blind gudgeon (Milyeringa veritas), the possibly extinct Lord Howe Island stick insect (Dryococelus australis) and the Queensland bottle tree (Brachychiton rupestris).
While many species possess unique combinations of adaptive features, some adaptations and ecological features can be regarded as typical of the Australian environment. These include sclerophylly and adaptations to frequent fire, aridity, an often unpredictable climate, high levels of salinity, low and patchy levels of soil nutrients, and variable hydrology.
Sclerophylly. Many Australian plants have leathery, hard, spiny or reduced leaves and relatively short internodes. These characteristics are known as sclerophylly and are believed to be adaptations to impoverished soils. Sclerophyllous characteristics are strongly represented in Australian Myrtaceae (including tea-trees and eucalypts), Proteaceae (grevilleas, hakeas, banksias, waratahs and relatives), Epacridaceae (heaths), and Mimosaceae (mainly acacias) (Barlow 1981).
Sclerophylly, while primarily an evolutionary response to poor soils, may have preadapted many Australian plants to drier conditions, such as occur in Mediterranean climates. It is thought that because of the generally weathered and infertile nature of Australian soils, sclerophylly has become progressively more widespread to an extent not matched on other continents (Barlow 1981).
Fire. Fire is an integral component of most Australian ecosystems and habitats. It is a natural environmental variable and fires occur with different intensities, times of year and frequencies across Australia. It is also a major management tool.
Many plants have adapted to particular fire regimes and a number of species rely primarily on fire to assist development of offspring (i.e. recruitment) such as Eucalyptus regnans (Gill 1981). In many cases fire can crack resistant seed coats, open fruit held on the parent plant and provide a rich medium for seedling growth. For some species, alteration of such fire regimes can threaten their viability. The reduced occurrence of fire has contributed to two species being considered endangered: Rutidosis leptorhynchoides and Swainsona recta (Leigh and Briggs 1992).
Salinity. Salt lakes are a prominent part of the Australian environment and in contrast to other continents, expanses of saline waters in Australia far exceed those of freshwater (McComb and Lake 1990). Some salt lakes such as Lake Corangamite in Victoria are permanent, whereas the majority, including Lakes Eyre, Frome and Torrens in South Australia are temporary and only fill occasionally. While species diversity is generally reduced with increased salt concentrations, the fauna and flora of salt lake communities possess major adaptations that aid survival in such extreme conditions, including rapid life cycles and mechanisms for salt excretion.
Variable hydrology. In addition to the variation in salt concentrations in saline lakes, the level and flow rate of water in Australian freshwater systems is also highly variable (McMahon et al. 1992; See figure 4 on page 44). Many inland streams and rivers only flow after unpredictable rains. After rain both the temporary and permanent water courses can flood vast areas and leave transient pools and lakes as they evaporate. Some adaptations, such as fish spawning only after a rise in river levels, are a response to this variability.
Australian plants and animals often interact in ways that are not only considered ecologically significant but in many cases are unique to Australia. These ecological interactions often result in co-evolution - that is different taxa evolving together. Many features of flowering plants, for example, can only be understood by observing the way they interact with animals; conversely many vertebrates and invertebrates have features that reflect their close association with plants. Such interactions between plants and animals include: pollination by insects and vertebrates; dispersal of seeds and fruits; the interactions between plants and the animals that feed on them; and plant defences against animal attack.
Australia's wetlands, coasts and islands have great significance as breeding and feeding refuges for migratory and wide-ranging species, some of which, such as Abbott's booby (Papasula abbotti; found on Christmas Island), are rare and endangered. Marine turtles and marine mammals, as well as seabirds, find feeding and breeding grounds along Australia's coastline and there are many Australian wetlands internationally recognised as valuable habitats for migratory birds. The Australian Antarctic Territory and Australia's subantarctic islands are also important for their refuge value and provide nesting sites for millions of seabirds.
A close examination of our native plants reveals great species richness and diversity, much of which is unique to Australia (endemic). Although two-thirds of the continent is dry, a large span of latitude provides a variety of climatic zones from the tropical north to the cool temperate south. This has allowed a rich variety of plant habitats to develop and with them the diverse flora that we enjoy.
Australia has an estimated 21-23 000 native species of vascular plants, some 85 per cent of which are unique to Australia. The more primitive seed-bearing plants (gymnosperms) are represented by a number of cycads (palm-like cone bearing trees) and conifers some of which are known from the fossil record. There are 14 endemic families of flowering plants (angiosperms) - the most for any country in the world.
Acacias (Mimosaceae; 950 species) and eucalypts (Myrtaceae; 800 species) dominate the landscape and are adapted to almost every habitat. Australia has the greatest diversity of the family Proteaceae in the world with 42 genera (860 species) from a world total of 72. Thirty-five genera are endemic to Australia (including banksias, grevilleas, hakeas, macadamias and waratahs).
Australia also has a large number of orchids with 1500 known orchid species mostly in the southeast and southwest. Lichens, which are associations of algae and fungi, are also very richly represented in Australia with about 2275 species.
Australian plants have undergone some remarkable adaptations. Sclerophylly is an adaptation to arid conditions in which the leaves are rigid and have a thick waxy cuticle. It is found in many plant groups such as some acacias, eucalypts and banksias. Many Australian plants are adapted to fire and some require fire for regeneration. Adaptations to fire include shedding large quantities of seed, a thick insulating bark, dormant buds, and woody rootstocks.
'Living fossils'
The origins of some of Australia's plants can be traced to before 160 million years ago when all the continents were joined. Fossils of the kauri pine and a cycad species have been found in 175 million-year-old fossil fish beds in New South Wales. Whereas the cycad is endemic to Australia, kauri pines also occur in Southeast Asia and the western Pacific. The origin of other species can be traced to a time when the southern landmass of Gondwana had split from Pangaea, for example the family Proteaceae, southern beeches and acacias. The rainforests of Australia, especially northern Queensland, harbour some of the world's most important links in plant evolution.
