Australia has some 8,300 islands, many of them home to threatened species. But humans have introduced rodents and predators such as feral cats and foxes to many of these islands, devastating native wildlife and changing entire island ecosystems. Removing invasive mammals has proven to be a very effective tool for protecting island species.
As a result, the federal government has made it a priority to remove invasive vertebrates from islands where they pose the most severe threats to native plants and animals.
But choosing where to remove those invasives is difficult. We don’t have complete information about the distribution of native species and threats across the nation’s 8,300 islands, and we haven’t been able to predict where eradication will have the most benefit.
However, in a recent study published in Nature Communications, our global team of scientists looked at islands around the world to consider where we can get the biggest bang for our buck.
It costs money to save species
The total cost of the recently completed rat and rabbit eradication on Macquarie Island was A$27 million. The proposed removal of rats from Lord Howe Island off New South Wales is expected to cost A$9 million.
Federal Environment Minister Josh Frydenberg has just announced funding to remove feral cats from five islands: Christmas Island, Dirk Hartog Island and the French Islands in Western Australia; and Bruny and King Islands in Tasmania.
Conservation dollars are limited, so it is important that these pricey interventions be focused on the islands where they will go the furthest toward conserving native island biodiversity.
Conversely, it is essential that we identify places where they won’t provide much benefit, either because a threatened species is likely to go extinct regardless of such interventions, or because the invasive species actually poses little threat.
We analysed the effects of invasive mammals on 1,200 globally threatened species across more than 1,000 islands to develop a model for where eradicating invasive wildlife will provide the greatest benefits to island species.
We estimate nearly half of threatened species populations on islands could disappear without conservation efforts. But targeted eradication could prevent 40-75% of these losses.
We found that just a few types of invasive mammals – rats, cats, pigs, mongooses and weasels – are most strongly associated with the disappearance of native species from islands.
Importantly, our study shows that the impacts of invasive mammals vary widely across the type of native species (native amphibians, birds, reptiles or mammals) and the conditions of the islands on which they live.
For example, we found that removing invasive mammals from small, dry islands could halve the extirpation risk for threatened native birds and mammals, but doing so on large, wet islands would have less benefit.
Australia’s most important islands
Our study included thirty-three Australian islands, home to 17 species of globally threatened birds, mammals and amphibians including the woylie (or brush-tailed bettong), Tasmania devils, black-browed albatross and Cooloola sedgefrog.
Eighteen of these islands are also home to introduced rats, cats or pigs, which potentially threaten native species with extinction.
Traditionally, we might assume that eradicating cats and rats would always reduce bird extinctions. However, our study suggests otherwise.
Rat or cat eradication may have little benefit on some islands. This is either because these invasive species have relatively minor impacts in some island environments, or because the native population is likely to go extinct regardless of conservation interventions.
So our study shows that of these 18 islands, eradicating invasive species on only two would likely prevent extinction of three native species populations. These are the eradication of cats and rats on Groote Eylandt in the Northern Territory, which would avert the extirpation (that is, the island-level extinction) of the northern quoll and northern hopping mouse; and the eradication of cats, rats and pigs on Flinders Island in Tasmania, which would avert the extirpation of the forty-spotted pardalote.
While this sounds like a tiny number, remember we haven’t looked at all of Australia’s islands and the species that live on them. Indeed, we only included species considered threatened at a global level. For the other islands not included in our study, species threatened with extinction at regional or national scales may – or may not – benefit from eradicating invasive species. As more information comes in on these islands, our analysis can suggest which of these we should focus on.
The second day of my ‘Red Centre Holiday 2016’ began early, with a 5.30 am departure from Nyngan. I actually tried to find a geocache out the front of the caravan park in the dark, but had to give up because of the waterlogged conditions. So it was on my way early to my next stop – another geocache along the way. In fact I searched for about a dozen throughout the day, finding most of them. So geocaching broke up the trip a little, getting me out of the car from time to time.
At this point it may not be a bad idea to explain geocaching – that way if you have no idea about what I’m talking about, you soon will have at least a rudimental understanding of it.
My first major stop of the day was at Cobar for breakfast. Following Cobar it was Wilcannia and then on to Broken Hill, where I spent the night at the Broken Hill Tourist Park. I stayed in a cabin again as I was still suffering badly from the flu.
ABOVE: Taking a Break
So there wasn’t a lot to report on for day 2. It was just another day of moving closer to my destination really – something which would take 5 days to achieve. On this second day I travelled 587 km (1169 km total for the whole trip so far).
ABOVE: On the Road
So once again it was the usual ‘house keeping’ before bed – updating the daily journal, reviewing the holiday budget, checking in on social media, and editing and uploading photos. Then it was off to bed for an early start the next morning.
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Visit the Red Centre Holiday 2016 web page at:
Our EcoCheck series takes the pulse of some of Australia’s most important ecosystems to find out if they’re in good health or on the wane.
Australia’s Top End, Kimberley and Cape York Peninsula evoke images of vast, awe-inspiring and ancient landscapes. Whether on the hunt for a prized barramundi, admiring some of the oldest rock art in the world, or pursuing a spectacular palm cockatoo along a pristine river, hundreds of thousands of people flock to this region each year. But how are our vast northern landscapes faring environmentally, and what challenges are on the horizon?
Above 17° south, bounded by a rough line from Cairns, Queensland, to Derby, Western Australia, are the high-rainfall (more than 1,000mm a year) tropical savannas. These are the largest and most intact ecosystem of their kind on Earth. With the exception of some “smaller” pockets of rainforest (such as Queensland’s Kutini-Payamu (Iron Range) National Park), the vegetation of the region is dominated by mixed Eucalyptus forest and woodland with a grassy understorey.
There is a distinct monsoonal pattern of rainfall. Almost all of it falls during the wet season (December-March), followed by an extended dry (April-November). Wet-season rains drive abundant grass growth, which subsequently dries and fuels regular bushfires – making these landscapes among the most fire-prone on Earth. The dominant land tenures of the region are Indigenous, cattle grazing and conservation.
These savannas are home to a vast array of plant and animal species. The Kimberley supports at least 2,000 native plant species, while the Cape York Peninsula has some 3,000. More than 400 bird and 100 mammal species call the region home, along with invertebrates such as moths, butterflies, ants and termites, and spiders. Many of the latter are still undescribed and poorly studied.
Many species, such as the scaly-tailed possum, are endemic to the region, meaning they are found nowhere else.
The general lack of extensive habitat loss and modification, as compared to the broad-scale land clearing in southern Australia since European arrival, can give a false impression that the tropical savannas and their species are in good health. But research suggests otherwise, and considerable threats exist.
Fire-promoting weeds such as gamba grass, widely sown until very recently as fodder for cattle, are transforming habitats from diverse woodlands to burnt-out, low-diversity grasslands. Indeed, the fires themselves, which are considered too frequent and too late in the dry season at some locations, are now thought to be a primary driver of species loss.
Notable examples of wildlife in trouble include declines of many seed-eating birds, such as the spectacular Gouldian finch, and the catastrophic decline of native mammal species, most prominently in Australia’s largest national park, Kakadu.
Added pressures include bauxite mining, forestry and cattle grazing. The latter activity exerts strong pressures on the characteristically leached, nutrient-poor, tropical soils. Most recently, changes to Queensland’s land-clearing laws have led to virgin savanna woodland being cleared.
It is likely some threats may also combine to make matters worse for certain species. For instance, frequent fires, intensive cattle grazing and the overabundance of introduced species such as feral donkeys and horses all combine to remove vegetation cover. This, together with the presence of feral cats, makes some native animals more vulnerable to predation.
This globally significant ecosystem, already under threat, is facing new challenges too. Proposals to use the region as a food bowl for Asia are associated with calls for the damming of waterways and land clearing for agriculture.
This is against a backdrop of climate change, which among other effects may bring less predictable wet seasons, more frequent and intense storms (cyclones) and fires, and hotter, longer dry seasons. Such changes are not only likely to harm some species, but could also make those much-touted agricultural goals far more difficult to achieve.
Great opportunities do exist in northern Australia, including carbon farming and expanded tourism enterprises. In some cases this might require difficult transitions, as already seen in parts of Cape York Peninsula, where often economically unviable cattle stations have become joint Indigenous and conservation-managed lands.
A key priority for the Great Northern Savannas should be to maintain people on country. It’s often thought that the solution to reducing environmental impacts is removing people from landscapes, but as people disappear so too does their stewardship and ability to manage and care for the land.
Importantly, and finally, we must also learn the historical lessons from southern Australia if we are to avoid making similar mistakes all over again, jeopardising the unique and precious values of the north.
Are you a researcher who studies an iconic Australian ecosystem and would like to give it an EcoCheck? Get in touch.
A group of killer whales are on the hunt. They work together to submerge and drown a whale calf. But then more whales appear.
The newly arrived humpbacks bellow a trumpet-like call, and wield their five-metre-long pectoral flippers like swords against the prowling killer whales.
The killer whales are driven away from the calf, and the humpbacks also move away. As they do, the killer whales turn back and descend on the calf once more. In response, the humpbacks swing around and return to the calf’s defence.
The humpbacks position themselves close to the calf, between it and the killer whales, potentially putting themselves in harm’s way.
This process continues and repeats for many hours, but it is not a calf of their own species, it is a grey whale calf.
This is not an isolated case. Robert Pitman, from the National Oceanic and Atmospheric Administration in the US, and his colleagues report more than 100 incidents where humpback whales have approached or actively intervened in killer whale hunting attempts.
Surprisingly, most of these have been predation attempts on other species, such as seals, other whales or even fish.
The question is: why would these humpback whales place themselves in danger by interposing themselves between one of their few predators – killer whales – and an individual of an entirely different species?
You scratch my back…
Altruistic behaviour is some of the most difficult to explain in evolutionary terms. In a biological context, altruism refers to cases where one individual’s behaviour provides a benefit to another individual at a cost to itself.
It doesn’t need to be as dramatic as throwing themselves on a grenade, but even placing themselves at a small disadvantage could jeopardise their chances of surviving and reproducing.
And if they don’t reproduce, then neither do the genes that encouraged the individual to be altruistic. This is why – all else being equal – you would expect altruistic genes to slowly disappear from a population over multiple generations.
But there are cases of altruistic behaviour in nature, particularly among closely related groups. One example is an individual meerkat who calls to alert its group to the presence of a predator, particularly as that call could make the predator more likely to notice the vigilant meerkat.
This kind of behaviour can evolve and remain stable in a population due to a process called kin selection. This is because the meerkat is closely related to the other members of its group, so it shares many genes with them. Even if it does end up sacrificing itself, if it helps its relatives survive, they may also be carrying the genes that encourage altruism.
Other cases of altruism in nature are supported by recriprocation: you scratch my back and I’ll scratch yours.
An example would be vampire bats that share blood meals. They do so on the assumption that their friend will return the favour at some later date.
However, for kin selection or reciprocal altruism to evolve, there needs to be a high level of social cohesion within the group.
For example, individuals need to be able to recognise who is a relative or a friend, and who is not. Presumably, you are less likely to put your neck on the line for a distant relative or for someone who is not likely to repay the favour.
So it might not be surprising that a humpback mother would vigorously defend her own calf from attacking killer whales. But why would a humpback approach and position itself between attacking killer whales and another whale’s calf?
As mentioned above, if an individual is prone to behave in a way that reduces their chance of surviving and reproducing, we would expect the genes that promote that behaviour to dwindle over generations and eventually vanish from the population. And even if an adult humpback puts itself at minimal risk by interfering with killer whales, minimal risk is more than zero risk by avoiding them altogether.
Pitman and his colleagues think there might be more social cohesion among humpbacks than we previously thought, and kin selection and/or reciprocal altruism could be playing a part.
Individual humpback whales return to the same region to breed. This means that there is a good possibility that humpbacks are related to their immediate neighbours. Pitman suggests this means it may be worth a humpback helping other humpbacks to protect their calves from killer whale attacks.
However, it is trickier to explain apparent altruism directed towards other species. Pitman and his colleagues explain that for the humpback whale, this intervention on behalf of other species is a “spillover” behaviour. They suggest it is an extension of the humpback whales’ “drive” to protect their own calves.
Humpbacks may have learned to respond to vocalisations of attacking killer whales, which trigger them to drive the killer whales away, regardless of the species being attacked.
If this tendency to drive away killer whales whenever they are attacking has helped humpbacks to protect their own calves, then the genes that promote it could be maintained in the population, even if other species benefit at times.
This interspecies altruistic behaviour may be “inadvertent” altruism – it can be altruism in the individual case but it is ultimately driven by self-interest.
When it comes to conserving the world’s oceans, bigger isn’t necessarily better. Globally, there has been an increasing trend towards placing very large marine reserves in remote regions. While these reserves help to meet some conservation targets, we don’t know if they are achieving their ultimate goal of protecting the diversity of life.
In 2002, the Convention on Biological Diversity called for at least 10% of each of the world’s land and marine habitats to be effectively conserved by 2010. Protected areas currently cover 14% of the land, but less than 3.4% of the marine environment.
Australia’s marine reserve system covers more than a third of our oceans. This system was based on the best available information and a commitment to minimising the effects of the new protected areas on existing users. However, since its release the system has been strongly criticised for doing little to protect biodiversity, and it is currently under review.
In a new study published in Scientific Reports, we looked at the current and proposed marine reserves off northwest Australia – an area that is also home to significant oil and gas resources. Our findings show how conservation objectives could be met more efficiently. Using technical advances, including the latest spatial modelling software, we were able to fill major gaps in biodiversity representation, with minimal losses to industry.
A delicate balance
Australia’s northwest supports important habitats such as mangrove forests, seagrass beds, coral reefs and sponge gardens. These environments support exceptionally diverse marine communities and provide important habitat for many vulnerable and threatened species, including dugongs, turtles and whale sharks.
This region also supports valuable industrial resources, including the majority of Australia’s conventional gas reserves.
A 2013 global analysis found that regions featuring both high numbers of species and large fossil fuel reserves have the greatest need for industry regulation, monitoring and conservation.
Not all protected areas contribute equally to conserving species and habitats. The level of protection can range from no-take zones (which usually don’t allow any human exploitation), to areas allowing different types and levels of activities such tourism, fishing and petroleum and mineral extraction.
A recent review of 87 marine reserves across the globe revealed that no-take areas, when well enforced, old, large and isolated, provided the greatest benefits for species and habitats. It is estimated that no-take areas cover less than 0.3% of the world’s oceans.
In Australia’s northwest, no-take zones cover 10.2% of the area, which is excellent by world standards in terms of size. However, an analysis of gaps in the network reveal opportunities to better meet the Convention on Biological Diversity’s recommended minimum target level of representation across all species and features of conservation interest.
We provided the most comprehensive description of the species present across the region enabling us to examine how well local species are represented within the current marine reserves. Of the 674 species examined, 98.2% had less than 10% of their habitat included within the no-take areas, while more than a third of these (227 species) had less than 2% of their habitat included.
Into the abyss
Few industries in this region operate in depths greater than 200 metres. Therefore, the habitats and biodiversity most at risk are those exposed to human activity on the continental shelf, at these shallower depths.
However, the research also found that three-quarters of the no-take marine reserves are sited over a deep abyssal plain and continental rise within the Argo-Rowley Terrace (3,000-6,000m deep). These habitats are unnecessarily over-represented (85% of the abyss is protected), as their remoteness and extreme depth make them logistically and financially unattractive for petroleum or mineral extraction anyway.
Proposed multiple-use zones in Commonwealth waters provide some much-needed extra representation of the continental shelf (0-200m depth). However, all mining activities and most commercial fishing activities are permissible pending approval. This means that the management of these multiple-use zones will require some serious consideration to ensure they are effective.
A win for conservation and industry
An imbalance in marine reserve representation can be driven by governments wanting to minimise socio-economic costs. But it doesn’t have to be one or the other.
Our research has shown that better zoning options can maximise the number of species while still keeping losses to industry very low. Our results show that the 10% biodiversity conservation targets could be met with estimated losses of only 4.9% of area valuable to the petroleum industry and 7.2% loss to the fishing industry (in terms of total catch in kg).
Management plans for the Commonwealth marine reserves are under review and changes that deliver win-win outcomes, like the ones we have found, should be considered.
We have shown how no-take areas in northwest Australia could either be extended or redesigned to ensure the region’s biodiversity is adequately represented. The cost-benefit analysis used is flexible and provides several alternative reserve designs. This allows for open and transparent discussions to ensure we find the best balance between conservation and industry.
Cordelia Moore, Research Associate, Curtin University; Ben Radford, Research scientist, Australian Institute of Marine Science; Clay Bryce, Senior Project Manager; Hugh Possingham, Director ARC Centre of Excellence for Environmental Decisions, The University of Queensland; Oliver Berry, Senior Research Scientist, CSIRO, and Romola Stewart, Adjunct Research Fellow, The University of Queensland