What's happening to Australia's biodiversity?

Some scientists believe that we are now witnessing the sixth mass extinction, the only mass extinction caused by a single species - humans.

Did megafauna that used to roam Australia become extinct because of climate change or because of hunting? How have population growth, habitat change and introduction of new species affected Australia's biodiversity?

Extinction over millions of years

Extinctions of species have been occurring since the first life forms evolved. It is estimated that about 30 billion species have lived since multicellular life evolved, but only about 0.01% of that number live on Earth today. There have been periods in the Earth's long history when mass extinctions have occurred. Some scientists believe that we are now witnessing the sixth mass extinction, the only mass extinction to be caused by a single species - humans.

Environmental change over thousands of years

Indigenous people have been interacting with Australia's natural environment for tens of thousands of years. During this time they undoubtedly influenced the course of evolution. Whatever the level of impact created by Australia's Indigenous people, they adapted their own lifestyles and survived in all parts of the continent for many thousands of years.

There is much debate about the kind of impact Indigenous people have had on this land. They used fire as a land management tool long before the arrival of Europeans, and this is thought to have affected vegetation patterns. Their hunting practices may have affected population levels of some animals, and the building of fish traps in coastal and inland rivers may also have had environmental effects.

While there have certainly been extinctions in Australia during the past 40,000 to 50,000 years, scientists are unsure about which, if any, were caused by Indigenous people. Did megafauna, such as Procoptodon (the giant short-faced kangaroo) or Diprotodon (the giant wombat-like marsupial), that used to roam Australia, become extinct because of climate change or because of hunting?

Environmental change over the last few hundred years

Since the arrival of Europeans in Australia, just over 200 years ago, there has been an extraordinary increase in the rate of environmental change and in the loss of biodiversity.

The main factor in the loss of biodiversity is the increased rate of population growth. This has led to habitat change through land clearing and urbanisation, hunting and exploitation. The introduction of new species is also a threat to Australia's biodiversity.

The greatest threat to biodiversity is human impact. Every day, more people need more space, consume and exploit more resources and generate more waste as populations continue to grow.

Human impacts reduce biodiversity in the following ways:

• We cause habitat change through agricultural, urban and industrial development, and the exploitation of natural resources.
• We pollute soil, water and air.
• We overharvest resources which reduces both population sizes and genetic diversity of commercial species, such as fish.
• We introduce invasive species which can damage land and water resources and sometimes bring diseases with them. In addition, they may compete with native plants and animals for food and shelter. Some animals, such as cats and foxes, directly destroy native species.
• We cause climate change by releasing carbon dioxide and other gases into the atmosphere, which alter the nature of ecosystems everywhere. One of the causes of increased levels of carbon dioxide is the burning of carbon-based fuels such as coal, oil and gas.

Many ecosystems have been lost during the past 200 years.

Some of these ecosystems include:

• 75% of rainforests and nearly 50% of all forests;
• over 60% of coastal wetlands in southern and eastern Australia;
• nearly 90% of temperate woodlands and mallee;
• more than 99% of south-eastern Australia's temperate lowland grasslands;
• over 83% of Tasmania's lowland grasslands and grassy woodlands;
• about 95% of brigalow scrub that originally grew in Queensland;
• over 90% of Victoria's grasslands.

Loss of species is a major threat to biodiversity in Australia. Species of animals and plants under threat may be listed in one of the following categories:

• Extinct
• Extinct in the wild
• Critically endangered
• Endangered
• Vulnerable
• Conservation dependent