Authors: Tim S Doherty, Alistair S Glen, Dale G Nimmo, Euan G Ritchie and Chris R Dickman
Published in:Proceedings of the National Academy of Sciences
Abstract
Invasive species threaten biodiversity globally, and invasive mammalian predators are particularly damaging, having contributed to considerable species decline and extinction. We provide a global meta-analysis of these impacts and reveal their full extent.
Invasive predators are implicated in 87 bird, 45 mammal, and 10 reptile species extinctions — 58% of these groups’ contemporary extinctions worldwide. These figures are likely underestimated because 23 critically endangered species that we assessed are classed as “possibly extinct.”
Invasive mammalian predators endanger a further 596 species at risk of extinction, with cats, rodents, dogs, and pigs threatening the most species overall.
Species most at risk from predators have high evolutionary distinctiveness and inhabit insular environments. Invasive mammalian predators are therefore important drivers of irreversible loss of phylogenetic diversity worldwide.
That most impacted species are insular indicates that management of invasive predators on islands should be a global conservation priority. Understanding and mitigating the impact of invasive mammalian predators is essential for reducing the rate of global biodiversity loss.
Doherty TS, Glen AS, Nimmo DG, Ritchie EG, Dickman CR (2016) Invasive predators and global biodiversity loss. Proceedings of the National Academy of SciencesPDFDOI
Authors: Trisha B Atwood, Rod M Connolly, Euan G Ritchie, Catherine E Lovelock,
Michael R Heithaus, Graeme C Hays, James W Fourqurean and Peter I Macreadie
Published in:Nature Climate Change, September 2015
Tiger sharks in Shark Bay, Western Australia, create a landscape of fear where sea turtles and dugongs preferentially forage in seagrass microhabitats that are lower in predation risk and have allowed Cabon stocks. Image credit Albert Kok via Wikimedia Commons.
Abstract
Predators continue to be harvested unsustainably throughout most of the Earth’s ecosystems.
Recent research demonstrates that the functional loss of predators could have far-reaching consequences on carbon cycling and, by implication, our ability to ameliorate climate change impacts. Yet the influence of predators on carbon accumulation and preservation in vegetated coastal habitats (that is, salt marshes, seagrass meadows and mangroves) is poorly understood, despite these being some of the Earth’s most vulnerable and carbon-rich ecosystems.
Here we discuss potential pathways by which trophic downgrading affects carbon capture, accumulation and preservation in vegetated coastal habitats.
We identify an urgent need for further research on the influence of predators on carbon cycling in vegetated coastal habitats, and ultimately the role that these systems play in climate change mitigation.
There is, however, sufficient evidence to suggest that intact predator populations are critical to maintaining or growing reserves of ‘blue carbon’ (carbon stored in coastal or marine ecosystems), and policy and management need to be improved to reflect these realities.
Atwood TB, Connolly RM, Ritchie EG, Lovelock, CE, Heithaus MR, Hays GC, Fourqurean JM, Macreadie PI (2015) Predators help protect carbon stocks in blue carbon ecosystems, Nature Climate ChangePDFDOI
Cats, rats and foxes have wrought havoc on Australian wildlife and ecosystems. Image credit Paul Hocksenar, Jude, Paul Hocksenar via Flickr.
Cats, rats and foxes have wrought havoc on Australian wildlife and ecosystems. Known as “invasive mammalian predators”, these are species that have established populations outside their native range.
Responsible for numerous extinctions across the globe, this group of species also includes American mink in Europe, stoats and ferrets in New Zealand, and mongooses on many islands.
One common solution is to kill these predators. However, research published this week in the journal Biological Conservation shows it’s much more complicated than that. Killing invasive predators often doesn’t work and is sometimes actually worse for native wildlife.
Killing for conservation
Management of the threats to biodiversity posed by invasive predators has focused on reducing their populations using lethal control. This includes poison baiting, trapping and shooting.
These programs have at times been successful at local scales and on islands. However, they are extremely costly and they often fail to stop declines of native fauna at larger scales.
Such management programs often occur with little regard for how they might interact with other threats that are impacting ecosystems. This has led to unpredictable outcomes of invasive predator control. Sometimes it doesn’t work or, worse, it results in a negative outcome for wildlife.
Key disturbances
We identified six disturbances with strong potential to increase the impacts of invasive predators: fire, grazing by large herbivores, land clearing, altered prey populations, the decline of top predators and resource subsidies from humans (such as increased food or shelter availability).
These disturbances interact with invasive predators in three main ways.
First, disturbances such as fire, grazing and land clearing result in a loss of vegetation cover, which makes prey more vulnerable to predation.
For example, small mammals in the Kimberley region of northern Western Australia experienced more predation by feral cats in an intensely burnt area, compared with patchily burnt and unburnt areas. Grazing by livestock similarly removes protective cover. Research shows that feral cats prefer to hunt in these areas because of the improved hunting success.
Second, increases in food or declines of competing top predators can allow populations of invasive predators to increase, thereby increasing their impact on native species.
For example, introduced prey species, such as rabbits in Australia, can support larger predator populations. This can lead to increased predation pressure on native species – a process termed “hyperpredation”.
The extinction of the Macquarie Island parakeet was attributed to this process. The parakeet co-existed with feral cats for more than 60 years, but declined rapidly to extinction following the introduction of rabbits to the island in 1879. Resource subsidies, such as garbage or hunters’ carcass dumps, can also support larger predator populations, leading to greater predation pressure.
Third, many of these disturbances also have a direct impact on native species, which is exacerbated by invasive predators. For example, habitat fragmentation reduces population sizes of many native species due to habitat loss. Increased predation by invasive predators can therefore make a bad situation much worse.
Getting it right
Our synthesis shows that management of invasive predators is likely to benefit from employing more integrated approaches.
Maintaining habitat complexity and refuges for prey species is one way that invasive predator impacts can be reduced. This includes improved management of fire and grazing. Lower-intensity fires that retain patchiness could reduce the predation-related impacts of fire on native species. Such approaches may be the best option where no effective predator control method exists, such as for cats in northern Australia.
Native top predators such as wolves in Europe and North America or dingoes in Australia can have suppressive effects on invasive predators. “Rewilding” is an option in some places where these species have declined. Where native predators conflict with livestock producers, guardian animals can often protect livestock from predation instead of lethal control.
If lethal control is used, it should be applied with caution. Selectively removing individual pest species from ecosystems can do more harm than good. Multi-species approaches are the best way to avoid such surprises and the order in which species are removed is an important consideration.
Rather than focusing on single processes, conservation managers should consider the multiple disturbances operating in stressed ecosystems and use management actions that address these threats in unison. Such integrated approaches are essential if further extinctions are to be avoided.
Authors: Tim S Doherty, Chris R Dickman, Dale G Nimmo and Euan G Ritchie
Abstract
Invasive species have reshaped the composition of biomes across the globe, and considerable cost is now associated with minimising their ecological, social and economic impacts. Mammalian predators are among the most damaging invaders, having caused numerous species extinctions.
Here, we review evidence of interactions between invasive predators and six key threats that together have strong potential to influence both the impacts of the predators, and their management.
We show that impacts of invasive predators can be classified as either functional or numerical, and that they interact with other threats through both habitat- and community-mediated pathways.
Ecosystem context and invasive predator identity are central in shaping variability in these relationships and their outcomes. Greater recognition of the ecological complexities between major processes that threaten biodiversity, including changing spatial and temporal relationships among species, is required to both advance ecological theory and improve conservation actions and outcomes.
We discuss how novel approaches to conservation management can be used to address interactions between threatening processes and ameliorate invasive predator impacts.
Doherty TS, Dickman CR, Nimmo DG, Ritchie EG (2015) Multiple threats, or multiplying the threats? Interactions between invasive predators and other ecological disturbances, Biological Conservation, 190, 60-68 PDFDOI
Authors: Christopher N Johnson, Mathew S Crowther, Chris R Dickman, Michael I Letnic, Thomas M Newsome, Dale G Nimmo, Euan G Ritchie and Arian D Wallach.
Abstract
There has been much recent debate in Australia over whether lethal control of dingoes incurs environmental costs, particularly by allowing increase of populations of mesopredators such as red foxes and feral cats.
Allen et al. (2013) claim to show in their recent study that suppression of dingo activity by poison baiting does not lead to mesopredator release, because mesopredators are also suppressed by poisoning.
We show that this claim is not supported by the data and analysis reported in Allen et al.’s paper.
The management of dingoes is a highly conflicted and frequently emotional issue in rural Australia. Image by Peripitus [CC-BY-SA-3.0] via Wikimedia Commons. Skull and Crossbones icon by Jens Tärning [CC-BY-SA-2.0] via the Noun Project.Johnson CN, Crowther MS, Dickman CR, Letnic MI, Newsome TM, Nimmo DG, Ritchie EG, Wallach AD (2014) Experiments in no-impact control of dingoes: comment on Allen et al. 2013. Frontiers in Zoology 11:17 PDFDOI
Sharks are critical to keeping environments in balance. Image credit: Terry Goss [CC-BY-SA-3.0] via Wikimedia CommonsWe have good reason to fear sharks and lions.
None of us wants to be an animal’s next meal.
And a number of recent fatal shark attacks in Western Australia have intensified the issue of human-predator conflict.
In response, the WA Government has introduced a shark cull to create “safe zones” for beachgoers – with the first killing on the weekend.
Thousands of people, including surfers, have since rallied against the move.
So what are the broader consequences of losing sharks and other large predators?
Landmark research in the international journal Science this month reviewed the conservation status and ecological roles of the world’s 31 largest carnivores.
Our study suggests that we should be greatly concerned about the ongoing loss of predators.
We studied lions, tigers, African wild dogs, leopards, cheetahs, wolves, lynx, otters, bears, hyenas and dingoes. The study spans all continents except Antarctica.
Alarmingly, roughly 75 per cent of all predators are declining and headed towards extinction.
So unless genuine and urgent efforts are made to conserve these animals, many of them could be gone for ever.
What happens when predators decline or, worse, disappear? In short, wherever we looked, we saw major environmental problems.
Research on Australia’s top predator, the dingo, tells a compelling story.
Over much of the continent, this native predator is shot and poisoned to protect livestock.
But science has now shown that by killing dingoes we make life easier for introduced foxes, cats, goats and pigs, as well as native kangaroos.
This has many impacts: most importantly the net loss of our native animals.
And in many cases, we actually lose more stock after killing dingoes. More sophisticated solutions to managing dingoes are available, like the use of livestock guardian dogs.
Globally, when top predators are lost, the number of mammals grazing on vegetation goes up, causing soil erosion, lower carbon sequestration and loss of habitat for native animals. Predators can also prevent the spread of disease.
In Africa, we are also seeing children forgoing an education to stay home and help their families protect crops from raids by rising numbers of Olive baboons, once kept in check by leopards and lions.
So what about sharks?
Like other top predators, they are critical to keeping environments in balance.
When large sharks are culled, numbers of rays and smaller fish species increase dramatically. Because these smaller species feed on commercially valuable fish, the economic impacts can be huge.
If endangered and legally protected species such as great white sharks are targeted and killed under government orders, we are surely within our rights to request a full cost-benefit analysis.
We need to make sure millions of taxpayer-funded dollars are not being wasted or even making things worse.
Persecuting sharks is not the answer. The management of any wildlife should be based on sound scientific evidence, not political rhetoric.
Clearly, predators have far-reaching ecological, economic and social benefits that are grossly underappreciated.
There is no doubt predators pose challenges, such as wolves attacking livestock and sharks attacking humans. But education and new management practices offer alternatives to culling.
When sharks were culled in Hawaii there was no long-term benefit because shark attacks occurred immediately after.
This is because many species of shark are migratory – some travelling thousands of kilometres. This means killing sharks in a local area only is doomed to fail.
Public education programs about sharks and installing shark exclusion nets is more sensible.
It is telling that many recent victims of shark attacks have come out to protest against the planned shark cull in WA.
Clearly, many people, including those most deeply affected, want smarter solutions to coexisting.
With all of this in mind, governments must find and encourage better ways for people and predators to live together. Failure to do so places us all at risk.
A live chat with Science journal associate editor, Sacha Vignieri.
In this 48-minute Google+ Hangout, we ask: what is it about large predators that makes them so important in ecosystems? How can we ensure their continued survival in a world with increasing human encroachment? And what would a world without predators look like if we fail?
ABC News’ Kate Brownlie-Smith speaks with Dr Mike Letnic about the survival of the world’s top carnivores and why it’s crucial for ecosystems they maintain.
NPR’s Christopher Joyce speaks to Michigan Technological University Research Professor and internationally renowned wolf expert Rolf Peterson and Science review lead author William Ripple about the interconnectedness of big predators in nature.
Without tigers, our ecosystems will suffer. Image credit: Sascha Kohlmann via FlickrHumans have an innate fear of large predators, and with good reason. Nobody wants to be a shark or a lion’s next meal.
But new research in the journal Science shows that our inability to live with these animals is putting their survival in great danger, and doing untold damage to the environment.
Through modifying the habitats of large predators or killing predators more directly, we are greatly compromising the ecosystems that they help to keep in balance — free of charge. In turn this environmental degradation creates many problems that have severe consequences for humans.
We ain’t lion, this predator stuff is a big deal. Image credit: Derek Keats via Flickr
Top dogs (and cats) under threat
For the first time, a team of researchers from the United States, Australia, Italy, and Sweden, and led by Professor Bill Ripple at Oregon State University, have analysed the effects of threats such as habitat loss, human persecution and reduced prey on the world’s 31 largest mammalian carnivores.
The species studied include lions, tigers, African wild dogs, leopards, cheetahs, wolves, lynx, otters, bears, hyenas and dingoes. Together they span all continents except Antarctica.
Alarmingly, more than three quarters of the 31 large carnivores are in decline, and 17 species occupy less than half of their historical distributions. The Red Wolf in the southeastern United States is now found in less than 1% of its historical range, and the Ethiopian Wolf in just 2%.
Hotspots of carnivore decline are southeast Asia, southern and East Africa, and the Amazon, where several large carnivores are declining. And in the developed world there are now few places where large carnivores remain.
In Australia, dingoes help keep introduced predators at bay. Image credit: Ars Electronica via FlickrAside from the intrinsic tragedy of losing any species, what should perhaps concern us even more is that we are only just beginning to understand and appreciate just how important large predators are to maintaining healthy ecosystems, and our dependence on the ecosystem services they deliver.
Ripple effect
Seven carnivore species in particular have been shown to have profound effects on the environment and cause what is known as “trophic cascades”. A trophic cascade is a ripple effect, where one species’ influence spreads through multiple levels of a food web.
Species for which this effect is most well-known are African lions, leopards, Eurasian lynx, cougars, gray wolves, sea otters and dingoes.
It’s hard being a VIP (very important predator). Image credit: Mike Baird via FlickrIn Australia dingoes greatly reduce kangaroo and red fox numbers, which in turn reduces grazing of vegetation and predation of native animals, helping to conserve and protect biodiversity.
In coastal North America, sea otters keep sea urchin numbers in check, which helps maintain kelp forests and benefits other marine species dependent on this habitat. But in this case otters might also offer a defence against climate change, as healthy kelp forests can grow rapidly and store large amounts of carbon.
And in Africa, a decrease in lions and leopards has coincided with a dramatic increase in Olive Baboons, which threaten farm crops and livestock, and spread intestinal worms. Baboons even impact education, as children have to stay home to defend their farms from raids.
Without lions and leopards, there’s no telling what baboons will do. Image credit: Justin Jensen via FlickrClearly predators have far-reaching ecological, economic and social benefits that are grossly underappreciated. There is no doubt predators pose challenges too, such as wolves attacking livestock. But education and new management practices offer ways forward. For instance, we could use guardian animals to protect livestock from predators.
Together we call on governments to end policies and management practices that are responsible for the ongoing persecution and loss of predators from our planet. Western Australia’s new shark plan is an example of management that fails to account for the science of big predators. Instead we need an international initiative that aims to conserve large predators and promote their coexistence with people.
I’ve just returned from a glorious two-week family holiday in sunny north Queensland. How I’ve missed the place, so much cool wildlife everywhere! Among the highlights were spotting a male cassowary with three chicks (my son is currently obsessed with these oversized birds), watching platypus swim from our front veranda on the Atherton Tablelands — if you’re looking for a biologist’s paradise you can’t go wrong here — and taking the kids spotlighting for NQ’s arboreal mammals. We missed out on tree kangaroos, alas, but we did see green ringtail, lemuroid, and Herbert River ringtail possums, coppery brushtail possums and long-nosed bandicoots. And at age five, Rohan seems to be well on his way to a successful career in field ecology, spotting the eye-shine of many possums himself.
But enough on holidays; what I’d like to update everyone on is the first results to roll in from our Big Desert work. As I’ve written previously, this is an incredibly remote and largely unstudied region, so there’s much to be discovered and learned. What have we found so far? Well, I’ll let the video, below, do most of the talking, but what’s most exciting is that we’ve confirmed there is a dog population in the park, and some individuals appear to look very much like dingoes. We always suspected this, but it’s nice to have positive confirmation. Another interesting result is that goats were not recorded on any of the cameras so far, as compared to the Murray Sunset National Park, to the north, where goats are very abundant, but dogs/dingoes are absent. It’s early days, the habitats of Murray Sunset and the Big Desert / Wyperfeld region are somewhat different, and I’m sure we’ll find some goats in the region soon enough, as they’ve been recorded there. But, it does suggest dingoes may be playing a role in keeping goat numbers down, as we know they do from other studies conducted in other parts of Australia .
Some may remember the Victorian Government recently reviewed the evidence for the existence of big cats; the legendary Black Panther. Well, we may just have found it ourselves! (second-last clip in the video). On a serious note though, cats appear to be relatively common, and great variation exists in their morphology (as seen on the videos). Cats are known to be a major factor behind the extinction of many native species, and new research also shows how they have large impacts on wildlife through the spread of toxoplasmosis. We’re keen to understand more about the role of foxes and dingoes in suppressing cats and therefore disease transmission, but more on that later…
No rest for the wicked. I’m off to Belfast next week to attend the 11th International Mammalogical Congress. I’ll be speaking about the dingo barrier fence and co-chairing a symposium on trophic cascades, ecological restoration and conservation of mammals. I’m really looking forward to a week of listening to mammal research from around the world, and perhaps just a wee Guinness or two as well.
In this interview with The Science Show’s Robyn Williams, I discuss encouraging dingoes as a top predator to help control lower predators such as a cats and foxes.
Authors: Leila A Brook, Christopher N Johnson and Euan G Ritchie
Abstract
Apex predators can benefit ecosystems through top–down control of mesopredators and herbivores. However, apex predators are often subject to lethal control aimed at minimizing attacks on livestock. Lethal control can affect both the abundance and behaviour of apex predators. These changes could in turn influence the abundance and behaviour of mesopredators.
The Australian dingo, Canis lupus dingo. Image: Angus McNab.
We used remote camera surveys at nine pairs of large Australian rangeland properties, comparing properties that controlled dingoes Canis lupus dingo with properties that did not, to test the effects of predator control on dingo activity and to evaluate the responses of a mesopredator, the feral cat Felis catus.
Indices of dingo abundance were generally reduced on properties that practiced dingo control, in comparison with paired properties that did not, although the effect size of control was variable. Dingoes in uncontrolled populations were crepuscular, similar to major prey. In populations subject to control, dingoes became less active around dusk, and activity was concentrated in the period shortly before dawn.
Shifts in feral cat abundance indices between properties with and without dingo control were inversely related to corresponding shifts in indices of dingo abundance. There was also a negative relationship between predator visitation rates at individual camera stations, suggesting cats avoided areas where dingoes were locally common. Reduced activity by dingoes at dusk was associated with higher activity of cats at dusk.
Our results suggest that effective dingo control not only leads to higher abundance of feral cats, but allows them to optimize hunting behaviour when dingoes are less active. This double effect could amplify the impacts of dingo control on prey species selected by cats. In areas managed for conservation, stable dingo populations may thus contribute to management objectives by restricting feral cat access to prey populations.
Brook L A, Johnson C N, Ritchie E G (2012) Effects of predator control on behaviour of an apex predator and indirect consequences for mesopredator suppression. Journal of Applied Ecology, 49: 1278–1286. doi: 10.1111/j.1365-2664.2012.02207.x
![Sharks are critical to keeping environments in balance. Image credit: Terry Goss [CC-BY-SA-3.0] via Wikimedia Commons](http://upload.wikimedia.org/wikipedia/commons/5/56/White_shark.jpg)
![Without tigers, our ecosystems will suffer. Image by Sascha Kohlmann [CC-BY-SA 2.0] via Flickr](https://euanritchie.files.wordpress.com/2014/01/tiger-flickr-sasha-kohlmann-1248x772px.jpg)
![We ain’t lion, this predator stuff is a big deal. Image by Derek Keats via Flickr [CC BY 2.0] via Flickr](https://euanritchie.files.wordpress.com/2014/01/lion-derek-keats-flickr-1248x772px.jpg)
![In Australia, dingoes help keep introduced predators at bay. Image credit: Ars Electronica [CC BY-NC-ND 2.0] via Flickr](https://euanritchie.files.wordpress.com/2014/01/dingo-ars-electronica-via-flickr-1248x772px.jpg)
![It’s hard being a VIP (very important predator). Image credit: Mike Baird [CC BY 2.0] via Flickr](https://euanritchie.files.wordpress.com/2014/01/sea-otter-mike-baird-via-flickr-1248x772px.jpg)
![Without lions and leopards, there’s no telling what baboons will do. Image credit: Justin Jensen [CC BY 2.0] via Flickr](https://euanritchie.files.wordpress.com/2014/01/baboon-justinjensen-via-flickr-1248x772px.jpg)
Applied ecology and conservation research group 
