September 7 is National Threatened Species Day in Australia. The date commemorates the death of the last known thylacine (or Tasmanian tiger, Thylacinus cynocephalus) in 1936. It is believed to have died from the cold after being locked out of its sleeping quarters in Hobart Zoo. Although neglect killed the last individual, the species had already received its death sentence despite being common in Tasmania before European settlement in 1803. Thylacines are believed to have been driven to extinction predominantly by hunting, with habitat destruction and disease also believed to have played a role. Since 1936, other species have followed the Tassie tiger down the extinction path; National Threatened Species Day encourages us to reflect on this, and think about how to protect our unique Australian fauna and flora into the future.
Australia’s fauna and flora
Australia has over half a million native species of fauna and flora, many of which are unique to our country (endemic). Endemic species include iconic mammal groups such as the monotremes (platypus and echidna); marsupials (which includes animals such as the koala, Tasmanian devil and kangaroos and wallabies); and of course the many species of eucalypts, wattles and other native plants.
Extinction in Australia is not just confined to mammals (birds, amphibians, reptiles, invertebrates and plants are also suffering from extinction or decline), but mammals are a useful group to focus on simply because people are more likely to notice when a mammal species disappears. This is in contrast to groups such as plants and insects, where new species are still being identified, sometimes just as they are going extinct, making it more difficult to determine when a species disappears and how the group as a whole is faring. However, given the number of mammal extinctions recorded in Australia, it is also possible that our mammals have actually had a higher rate of extinctions than other groups such as birds.
Australia is one of the world’s leaders in mammal extinctions. Since European settlement, approximately 10% of our 273 endemic terrestrial mammals have gone extinct. The exact number varies depending on source, as it is hard to define exactly when something has gone extinct. However, at least 27 endemic mammal species have gone extinct, with some sources recognising 29 extinct species. Many more endemic mammal species are also threatened with extinction. For comparison, North America has only had one terrestrial mammal species go extinct since its European settlement.
Why are our native mammals declining?
Australia’s native mammals are subject to many synergistic threats, including habitat loss, introduced species and climate change. Similar to other continents, species are losing habitat due to human development. The overall loss of habitat reduces the number of individuals that are able to survive due to the reduction in appropriate resources. The remaining appropriate habitat is often fragmented, meaning that populations can become more isolated, eventually reducing genetic diversity and increasing the chance of problems due to inbreeding. Individuals are also more likely to be killed while moving from one fragmented area to another to find a mate or new food source, as they are more likely to be hit by traffic or attacked by predators.
One of the main factors believed to be driving Australia’s endemic mammals extinct is introduced species. The newcomers may be predators, competitors or simply contribute to environmental degradation. Predation from cats and red foxes has driven the large number of extinctions of small to mid-sized mammals which mainly live or feed on the ground. Black rats can outcompete our native rodents, reducing population densities of the natives. Herbivores introduced for agriculture, such as cows and sheep, can reduce the number of types of native mammals in an area through habitat degradation and competition for resources. The environmental degradation, in turn, makes the native species more vulnerable to predation as there is less protection in the habitat for them. Changed fire regimes have also been implicated in the decline of Australia mammals, as the increase in hotter fires in some areas, and decline in fires in other areas, has changed the environment. The fires can also reduce the habitat protection from predators.
A more recent threat is climate change, which is increasing the risk of extinction for species globally. This is because many species are likely to have difficulties moving their geographic range to meet their environmental requirements as climatic changes occur. Climate change can also cause habitat loss (such as from rising sea levels) and adversely affect food sources, reproduction and migration. Unfortunately, Australia is not immune to this and effects from climate change are already occurring; the Bramble Cay melomys (Melomys rubicola), a native rat which lived on Bramble Cay in the Torres Strait, is believed to be the first mammal species globally driven to extinction by anthropogenic climate change.
How the Government is fighting decline
Australia’s main piece of environmental legislation, the Environment Protection and Biodiversity Conservation Act 1999, conserves biodiversity by providing ‘a legal framework to protect and manage nationally and internationally important flora, fauna, ecological communities and heritage places’. This includes species listed as threatened under the Act. Through the Threatened species strategy, the Government has committed to a conservation approach of ‘science, practical action and working in partnership’ with stakeholders including state governments and Indigenous groups. The Government is also financially supporting conservation through, for example, the Threatened Species Recovery Fund (as part of the Threatened species strategy) and by supporting relevant research through bodies such as the Australian Research Council. Hopefully, these initiatives will help slow the decline of our native species.