The Biological Diversity of Australia
Australia has one of the highest species richness of a country in the world. Now this is a bit of a loaded statement, and it's full of complications as well as justifications. One of the reasons it's so diverse, is simply because it's so big. And it's cheating a bit, because obviously the more area you have, the more species you're bound to have. Some of the other most biologically richest countries are also the biggest; Indonesia, Brazil, India, the U.S.A. As a country, Australia is the sixth biggest in the world (after Russia, Canada, China, India and the U.S.A.). It covers over 7.5 million square kilometres (Nicholson 1997), and is roughly the size of the continental United States, without the state of Alaska. If you look at the figure below, you can see that like the U.S.A, it is longer than it is tall, but unlike that country (which misses out on the tropic of cancer).
The two countries are fairly similar in terms of numbers of species of larger animals, such as birds and mammals, but the large tropical portion of Australia means there's a higher diversity of smaller organisms, such as lizards, frogs and insects.
But the real biodiversity of Australia resides in it's endemics.
Australia is referred to as the 'island continent'. It's often thought of as the biggest island in the world. But biologically, it's better to think of it as the smallest continent, as it has it has it's own distinct flora and fauna that defines it as a very distinct biogeographical realm that easily distinguishes itself from the Earth's other great biological regions, which roughly correlate with the other continents. And it's this distinct flora and fauna that is the most important and celebrated part of Australia's biodiversity.
Most Australians think of their own country as 'the bush'; grasses, eucalypt trees, and fires. The 'bush' refers generally to the great open forests and woodlands that cover so much of the east coast, the top third, and the southern parts of the country. the tropical version of the bush, known as 'tropical open forest, and woodlands'. It's also known locally as the 'savannah', and indeed it is similar in many ways to the savannas or grasslands of Africa, although strictly speaking, we do have our savannas, more in the gulf country. But it's a nice evocative colloquial term, just as 'jungle' is for the 'tropical rainforest'. These great open forests and woodlands extend into the tropics and cover the entire top third of the continent. What you'll see between Kuranda and Mareeba, and in the wetlands, extends all the way across and looks pretty much the same the whole way. It's the landscape of Cape York, of much of the Kimberly region in the north west, and of Australia's largest national park, Kakadu. The dominant life form of the open woodlands are the grasses. This family is of course one of the most important, and biggest, of families or any organism in the world. Grasses are biodiversity. But one of the most important components of these tropical woodlands, as with many ecosystems around Australia, are Eucalyptus.
Eucalyptus is not even the most common genus of plants, that record belongs to the Acacia, but Eucalyptus symbolises Australia's vegetation and ecology and national identity in so many ways. There are hundreds and hundreds of species, in fact nobody really knows how many species there are, and if you read different sources, you'll get different answers, ranging anywhere from 400 to 900 species. They represent biodiversity in every sense of the world, for they also exhibit broad genetic diversity within the species, with some of the wider ranging species, like the 'Coolibah', which you might recognise from the song 'Waltzing Matilda', and is found along dry river beds in the drier parts of the country and looks very different. Some species intergrade with other species and naturally produce hybrids in different areas. They range in size from the bush like multi-stemmed mallees, to the giant Mountain Ash pictured here, which is the tallest flowering plant in the world. They nearly always have those drooping olive leaves but not always, some are slightly deciduous, some have bright green leaves.
Australia has many birds that are found elsewhere in the world, and when you hear about Australian egrets, cranes, storks, ducks, geese, swans, jacanas, terns, gulls, sandpipers, plovers, owls, kingfishers, pigeons, parrots, and cuckoos, they are related to the ones you know and love. However, they will have different types,
The kingfishers of course have the giant laughing, cackling kookaburras, there are fat rainbow coloured fruit pigeons that live high in the rain forest canopy, and a great range and diversity of parrots, like this sulfur crested cockatoo.
But again, Australia's biodiversity lies in those species that are found nowhere else. We have over 750 birds recorded living in or visiting it's shores, but we have more endemic species than any other country in the world. That is, 300 of our species are found nowhere else on Earth.
Further, genetic testing over the last few decades has revealed that most Australian birds are not at all closely related to those overseas, even though they may superficially resemble them. And so, we have robins that are not robins, flycatchers that are not flycatchers, magpies that are not magpies, magpie larks that are not magpies nor larks, cuckoo-shrikes that are not cuckoos nor shrikes,
Probably the most important of these endemic birds are the `Honeyeaters'. This is the biggest family of birds in Australia. In a typical survey they can account for more than half the birds living in any given area (Simpson et al 1996).
They should look familiar because they are in many ways the ecological equivalent of the American Hummingbirds. Like them, they're nectar feeders, and thus vital pollinators for many Australian plants. However, most honeyeaters are much bigger than the overseas nectar feeders, and most are not delicate enough to hover. And Australian flowers have probably co-evolved with these giant hummingbirds; our flowers are huge and gaudy, and often dripping with nectar. They range in size from this tiny, hummingbird-like fella called an 'eastern spinebill' (above) to 'friarbirds' the size of pigeons, that resemble small vultures.
But I guess it's not the birds most overseas visitors think of when they hear of Australia, it is of course the mammals...
I guess we all know what a mammals is; they make up a group that is united by a combination of features including body hair, feeding the young with milk from glands, and being warm-blooded (Strahan 1998). But they're further divided into three subclasses; the monotremes, the marsupials, and the placentals. The 'monotremes' include only three mammals, the Platypus and two species of Echidna, and are found only in Australia and/or New Guinea, and they are the only mammals to lay eggs. The Platypus is probably the most interesting mammal in the world. Marsupials are of course the koalas, the kangaroos, the wombats, numbats, quolls, quokkas, antechinus and thylacines. And the placentals are the rest of the mammals, cats, dogs, cows, sheep, monkeys and people.
And once again, Australia's biodiversity lies in it's species that are found nowhere else on Earth. Australia is the only continent to have all three types of mammals; the egg layers, the marsupials, and the placentals.
We have about 300 species of mammals in total, and many visitors and residents of the continent assume that most Australian mammals are marsupials. However, this is not at all accurate, for only about half of the continents native mammals are marsupial. The rest are dominated by two very familiar groups; the rats and mice, and the bats.
In fact, it is often useful to distinguish Australia not on what unusual mammals it does have, but on what mammals it lacks. Squirrels, primates, cats, dogs and hoofed animals (antelope, cattle, pig or deer) have representatives on practically every habitable continent, but none are truly native to Australia.
But lets not deny it, it's most famous for it's marsupials. This group includes many members in South and Central America, and even one species in North America. However, it is in Australia and surrounding islands where the marsupials have really evolved to such a spectacular effect. And they have exploded into a diverse array of forms, to fill in the niches that are filled elsewhere by other mammals. Thus the monkeys and squirrels are replaced by possums, the carnivores are replaced by tiger cats or quolls and others, and the deer and antelope are replaced with kangaroos and wallabies.
And if there is one type of mammal that most typifies the Australian continent, it is these kangaroos. Below is an Eastern Gray Kangaroos', probably the most familiar of all kangaroos.
It's a typical kangaroo, but it's just one species. Now, a lot of first time visitors to Australia from other countries knows there's kangaroos in Australia, but they often think there is only one type. And, indeed, there is one common body plan to the kangaroos, cute little shorter front legs or paws, and elongated back legs that have very long stretched out toes, and long tails. But there is in fact over 60 species of different types of kangaroos. There are big red kangaroos, gray kangaroos, wallabies, rock wallabies, tree kangaroos, wallaroos, pademelons and quokkas. There are kangaroos that live in the desert, kangaroos that live in the woodlands, kangaroos that live within boulders, and kangaroos that live in the rainforest. When we think of kangaroos, we don't normally think of them living in the jungle, but in the rain forest here in the wet tropics, there are several different types. There are small rainforest wallabies called 'pademelons', a tiny bunny rabbit sized kangaroo called a 'musky rat kangaroo', and kangaroos that live in the canopy, called 'tree kangaroos'.