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.
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.
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 July 30 2015.
Tim Doherty is PhD Candidate at Edith Cowan University.
Chris Dickman is Professor in Terrestrial Ecology at University of Sydney.
Dale Nimmo is Lecturer in Ecology at Charles Sturt University.
Euan Ritchie is Senior Lecturer in Ecology, Centre for Integrative Ecology, School of Life & Environmental Sciences at Deakin University.
South Australia is facing the closure of its Northern and Playford B power stations and Leigh Creek coal mine, after Alinta Energy yesterday announced plans to shut them ahead of schedule. It will cost 438 jobs in the coal-mining and coal-fired electricity industries. But this threat to employment could be transformed into an opportunity for creating many new jobs in renewable energy.
The South Australian electricity system could be operated entirely on scaled-up, commercially available, renewable energy sources. This is the conclusion of my forthcoming report (to be published next week) to the Conservation Council of South Australia.
Our modelling at UNSW Australia shows that the SA system could be supplied mainly by a mix of wind power; solar photovoltaic (PV) panels, both on rooftops and in large solar farms; and concentrated solar thermal (CST) power with thermal storage. Gas-fired turbines and demand management via “smart” meters and switches would manage the infrequent small lulls in wind and solar supply.
I estimate this transition would take 15–25 years, during which time the natural gas fuel for the gas turbines would be gradually replaced by biofuels from agricultural residues – thus making the system fully renewable. There would be increased trading of electricity with Victoria and possibly over a new transmission link to New South Wales.
Already a leader… by Australian standards
SA is already the leading Australian state in non-hydro renewable energy, with about 40% of annual electricity consumption now coming from wind and sunshine. SA has already shown that it can operate reliably and stably for hours when the contribution of variable renewable energy reaches two-thirds of demand, and last weekend wind power and gas coped admirably when the coal-fired Northern power station went unexpectedly offline.
In Europe, the idea of a state moving to 100% renewable energy would not be regarded as a controversial proposal. The north German states of Mecklenburg-Vorpommern and Schleswig-Holstein are already operating on 100% net renewable energy, mostly from wind. The “net” indicates trading with each other and their neighbours. Although SA has transmission connections to Victoria only, it has the advantage over northern Europe that it is very sunny as well as windy.
Bye bye baseload
Our calculations show that SA does not need any baseload power stations, such as coal or nuclear. Indeed, the lack of operational flexibility of coal and nuclear makes them poor partners for high penetrations of variable renewable energy. The SA system has already operated reliably for long periods without its coal-fired stations, as last weekend’s incident demonstrated.
Moving fully to renewable energy will deliver environmental, social and economic benefits. The transition would reduce SA’s greenhouse gas emissions, air pollution and associated respiratory diseases. It would cap electricity prices.
SA could create a wide range of new jobs in manufacturing, installation, grid connection, technical support and sales, which could help to compensate for the forthcoming job losses in its coal industry.
As for the nuclear question, the multinational financial analyst Lazard estimates the average costs of subsidized new nuclear energy in the United States in 2017 to be 12.4–13.2 US cents per kilowatt hour (kWh), compared with unsubsidized costs of 3.7–8.1 c/kWh for onshore wind, and 7.2–8.6 c/kWh for large-scale solar PV. For Britain’s proposed new nuclear power station Hinkley C, the UK government is offering a guaranteed price of 9.25 p/kWh (14 US c/kWh) increasing with inflation for 35 years. Thus new nuclear energy prices are roughly double those of onshore wind, and also higher than those for solar farms.
Compared with nuclear power, an appropriate mix of renewable energy sources is just as reliable, less dangerous, cheaper, emits less carbon dioxide overall, offers a wider range of environmental, health and employment benefits, can be implemented much more rapidly, and is more likely to enjoy community support.
What’s more, a nuclear power station (600 megawatts or more) would be too big for the SA grid system, and smaller “modular” reactor designs are not yet commercially available. Renewable energy, in contrast, is technically and economically feasible, and environmentally and socially desirable.