Tag Archives: predators

Invasive predators and global biodiversity loss

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


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 Sciences PDF DOI


Predators help protect carbon stocks in blue carbon ecosystems

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 Shark

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.


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 Change PDF DOI

The Conversation: Killing cats, rats and foxes is no silver bullet for saving wildlife

By Tim Doherty (Edith Cowan University), Chris Dickman (University of Sydney), Dale Nimmo (Charles Sturt University) and Euan Ritchie (Deakin University). 

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.

Reducing resource subsidies is a simple way of reducing food resources for invasive predator populations.

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.

The paper is free to download until 30 July 2015.The Conversation

This article was originally published on The Conversation. Read the original article online, including reader comments.

The Conversation


Multiple threats, or multiplying the threats? Interactions between invasive predators and other ecological disturbances

Authors: Tim S Doherty, Chris R Dickman, Dale G Nimmo and Euan G Ritchie


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 PDF DOI

Experiments in no-impact control of dingoes: comment on Allen et al. 2013

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.


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 PDF DOI

Herald Sun: Predators such as sharks essential for world’s health

Sharks are critical to keeping environments in balance. Image credit: Terry Goss [CC-BY-SA-3.0] via Wikimedia Commons

Sharks are critical to keeping environments in balance. Image credit: Terry Goss [CC-BY-SA-3.0] via Wikimedia Commons

We 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.

This post was originally published in the Herald Sun. Click here to read the original article, including reader comments