The Extinction and Conservation of Australia’s Biodiversity

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Words | Jodie Ramodien

Grapeshot interviews Jaco Le Loux, Associate Professor in the department of Biological Sciences at Macquarie University and Dr. Sandy Ingleby, the Mammal Collections Manager at the Australian Museum.

In conversation with Jaco Le Loux:

What are some of the major threats posed to Australian wildlife?

Like elsewhere in the world, the main culprits are human-mediated climate change, habitat destruction, and invasion by exotic species. Australia is special in that the continent has been isolated for tens of millions of years and has therefore exchanged very little biota with other continents historically. This, in part, resulted in the evolution of very remarkable animals and plants, found nowhere else on Earth, that may be particularly vulnerable to novel threats.

How has climate change affected biodiversity in Australia?

There is no doubt that climate change negatively impacts most species, especially those with small population sizes and limited dispersal opportunities, like threatened plants. Climate and its interactions with other abiotic conditions, as well as with organisms themselves, are complex. Therefore, ascribing the extinction of a particular species to climate change per se is difficult. Yet, the impacts of climate change on biodiversity is undeniable. For example, sea surface temperatures were largely responsible for the low rainfall and humidity that Australia experienced in 2019 which, in turn, contributed to the devastating 2019-2020 Black Summer fires. Some scientists have estimated that more than 800 million animals may have perished in NSW alone during these fires. We also know that large parts of the natural habitats of many native species were burned down. The recent Bureau of Meteorology (BOM) “State of the Climate 2020” report suggests that Australia will experience even warmer temperatures, drier periods, and more extreme events in the future, spelling disaster for our unique biodiversity.

What is the impact of invasive species on extinction rates among Australian flora and fauna?

The impacts of invasive species on native Australian biodiversity are massive. Let’s consider mammal extinctions. In other parts of the world the primary drivers of mammal extinctions are habitat loss and hunting, but in Australia only two (!) invasive species (cats and European red foxes) have been responsible for the extinction of most of the 30 or so extinct native mammals. Some have argued that Australia’s historical isolation may underlie these devastating impacts, as many native Australian species lack evolutionary experience to mesopredators like cats and foxes. Similarly, native plants with little or no evolutionary experience with invasive animals like camels and brumbies (Australia has no native hoofed animals) have been severely impacted through trampling and grazing.

Have we been able to improve the status of threatened species through conservation practices?

There is a lot going on in the conservation arena in Australia, with numerous initiatives at both state and national levels. Biosecurity in Australia is arguably one of the most significant initiatives. While biosecurity is primarily focussed on safeguarding the country from unwanted pests and diseases of agricultural crops, there is no doubt that native biodiversity is benefitting from the stringent measures that are in place at all major ports of entry to the country. Excellent programs also exist at state level. For example, the NSW Saving our Species program is one of the biggest commitments ever undertaken by any state to conserve native biodiversity. The program involves various expert and stakeholder groups and aims to secure the future of threatened species in the wild and to control/manage the key threats they face. For example, as a ‘climate-ready’ strategy, Saving our Species coordinates the translocation of threatened plants to areas outside their current distributions that will have suitable climate conditions in the future. Similar programs have saved many of Australia’s mammals from certain extinction through captive breeding programs and translocations to predator-free islands.

What are some of the insights you have gained as a result of your research?

My own research is focussed on invasive species biology and plant ecology. I have learned that the impacts of invasive species can be highly complex and, importantly, context-dependent. This means that, while negative impacts on biodiversity by invasive species will always be evident, it is almost impossible to predict the types of impacts that will manifest. My research has also found current rates of plant extinction to conform to the so-called ‘sixth mass extinction,’ akin to the sudden disappearance of dinosaurs. While extinction has occurred throughout Earth’s history, we showed that, over the last 300 years, plants have been going extinct up to 350 times faster than historical rates. These estimates are likely to be gross underestimates and I am certain that we will witness the loss of a significant number of plant species in the near future.

Is there anything you would like to add or that you would like readers to know in regards to this issue’s theme of Extinction?

Be amazed by the variety and splendour of all things living. Without this biodiversity humanity cannot exist. The air that we breathe, the water we drink and the food that we eat, all depend on healthy ecosystems, and therefore biodiversity.

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In conversation with Dr. Sandy Ingleby:

What is Australia’s track record like when it comes to mammal extinctions?

Australia has an extremely poor record when it comes to mammal extinction. Over 30 mammal species have become extinct since European settlement in Australia and many more have vanished from large parts of their former range on the mainland. This represents nearly one third of all mammal extinctions worldwide over the last 500 years—quite a record when you think about it. This is even more significant when you consider that nearly all these species were only found in Australia—so extinction here means extinction everywhere.

Why is this? Why have Australian mammals fared so badly compared to those in other parts of the world?

Australia has a unique suite of mammals-egg laying mammals such as the platypus and the echidna, marsupials like wombats, koalas and, kangaroos, and a diverse range of native rodents and bats. Most mammals here are what we call ‘endemic’ in that they occur nowhere else on earth. Being an island continent, most mammals have evolved in isolation from the fauna of other regions of the world. Most notably exotic predators such as foxes and cats. So, when these two highly effective predators arrived with Europeans they wreaked havoc on the native mammals and are still doing so today—over large parts of the continent. Other factors such as habitat loss are also major contributors but certainly cats and foxes had a huge impact very early on.

What are some of the mammals that have become extinct since European settlement? 

The most well-known Australian mammal to go extinct in recent rimes is undoubtedly the Thylacine or Tasmanian Tiger as it was also known. This beautiful animal was the largest marsupial carnivore to make it to modern times but the last known individual tragically died in a Hobart zoo in 1936 and no confirmed sightings have occurred since then. The Thylacine was unusual in that it was quite large – around the size of a Labrador. Most mammal extinctions since the mid-1800s have been of so-called medium sized mammals – those ranging in size from a large mouse to a small kangaroo. Most vanished without much being known about them—except of course by First Nations people who would have had a detailed knowledge of many aspects of their biology. Most mammals that disappeared were either small wallabies like the eastern hare-wallaby, crescent nailtail wallaby, and broad-faced potoroo, bandicoots or bilbies such as the pig-footed bandicoot and lesser bilby or native rodents such as the lesser stick-nest rat or long-tailed hopping mouse. Species that were an important part of our biodiversity and that now exist only as specimens in museum collections or old photographs and drawings.

Have any mammals recently become extinct?

Just last year, in February 2019, the bramble cay melomys, a small native rodent that lived on a tiny sand island in the Torres Strait was declared extinct. In another first for Australia it was the first mammal to have gone extinct as a direct result of climate change—its island home was simply washed away by increased storm activity due to climate change. Prior to that, in September 2017, a small insectivorous bat found only on Christmas Island, the Christmas Island pipistrelle, was also declared extinct. So that’s two mammals in yours and my lifetime.

What are we doing to stop the decline of Australia’s mammal biodiversity?

Many mammal species have been put on the threatened species list in recognition of their plight but this is just the first step. Where certain mammal species have disappeared from parts of their former range but survived in other areas such as on predator free islands those animals are being used in captive-breeding programs. These captive bred animals are then released into predator free areas or enclosures in efforts to “rewild” or repopulate those areas. Museum collections like the one at the Australian Museum play an important role here as we are the custodians of specimens from these extinct populations and these can be used to help choose the most appropriate genetic stock to be used for the introductions. These reintroductions have been successful in some cases but they rely on ongoing control of fox and cat numbers. However, at the same time we are continuing to impact important habitats of many threatened species and further fragment existing habitats and that can only end badly.