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Thinking big gives top predators the competitive edge
Dingoes could be the key to controlling red foxes and other invasive predators, but only if we encourage them in large enough numbers over a wide enough area, our research shows.
Interest in re-introducing or restoring top predators, like dingoes and wolves, has been fuelled by recent studies demonstrating their important roles in their ecosystems. They can especially be vital in suppressing the abundance of lower-order competitors or “mesopredators”, like red foxes and possibly feral cats (which can have devastating effects on native species).
But researchers have found top predators aren’t always successful in reducing mesopredator numbers. Until now, such variation has been linked to human presence, land-use changes and environmental factors such as landscape productivity.
However, our research, published yesterday in Nature Communications, found that a key factor for success is high numbers of dingoes and wolves across their natural range.
The density effectIf you look at how species are typically distributed across a landscape – their range – ecological theory predicts there’ll be lower numbers at the outer edges of their range.
If you do need large numbers of top predators to effectively suppress mesopredators, the core of their range is potentially the best place to look.
We tested this idea, looking at the dingo in Australia and the grey wolf in North America and Europe. The mesopredators included the red fox in Australia, the coyote in North America and the golden jackal in Europe.
We looked at three regions in our study. Predator distribution is shown for: a) coyotes (hashed) and grey wolves (orange) in Saskatchewan, North America (present day); b) golden jackals (hashed) and grey wolves (orange) in Bulgaria and Serbia (present day); and c) red foxes (hashed) and dingoes (orange) in Queensland, Australia (in the 1950s). Predator images: Doug McLaughlin; Bobby Tamayo, Harley Kingston/flickr, Larry Lamsa/flickrWe used information from bounty hunting programs, as these provide data on predator numbers across a wide geographical area. In the case of Australia we used historic data from the 1950s, as this is the most recent reliable information about red fox and dingo distribution. The actual population numbers of red foxes and dingoes have changed substantially since then, but the nature of their interactions – which is what we were investigating – has not.
We determined that top predators exist in higher numbers at the core of their ranges in comparison to the edges. We then looked at mesopredator numbers across the range edges of their respective top predator.
Predator bounties and top predator range edges in each continent. The number of bounties (representing the number of animals killed) are given for each hunting unit in North America (collated from 1982 to 2011) and Europe (collated from 2000 to 2009), whereas each square in Australia represents the number of bounties in a 100-by-100km area (collated from 1951 to 1952). Top predators are in a–c. Mesopredators are in d–f. Darker colours within each hunting unit indicate greater bounty return numbers and, by inference, a higher abundance for the respective predator. Dashed black lines indicate top predator range edges. Australia was divided into two sections for the analysis (east and west) as shown.The results, which were consistent across the three continents, suggest that top predators can suppress mesopredators effectively (even completely) but only in the core of their geographic range, where their numbers are highest.
In other words, abundant top predators can exert disproportionate mesopredator control once their numbers increase past a certain point.
Example of the results from Australia (western side of Queensland). The blue lines indicate the abundance of each predator (note that the values on the y-axis are scaled so do not reflect actual numbers). The black dashed line indicates where there is a sharp change in predator abundance (the breakpoint). The red dashed lines indicate 95% confidence intervals (a measure of uncertainty) either side of the breakpoint. Distance values less than zero relate to areas outside the dingoes’ range, while distance values greater than zero relate to areas within the range. In summary, abundances of the red fox decline sharply as you move further into the range of the dingo. The ‘enemy constraint hypothesis’The relationship we uncovered is now formalised as the “Enemy Constraint Hypothesis”. It could apply to other predator dyads, where two animals compete for similar resources – even relationships involving parasites and pathogens.
Our findings are important for understanding species interactions and niches, as well as the ecological role of top predators. It could explain why other studies have found top predators have little influence on mesopredators: they were looking at the edge, not the core, of the top predators’ range.
This is a conceptual model of the Enemy Constraint Hypothesis. On the edge of a top predator’s range, mesopredator abundance should decline as top predator numbers increase. The breakpoint for the mesopredator indicates where their population nears zero. The breakpoint for the top predator indicates where their abundance starts to decline sharply on the edge of the range. How many top predators do we need?Dingoes can be vital for reducing red fox and possibly feral cat numbers. In our case studies the ranges of each top predator were limited primarily by human use of the land and intensive shooting, trapping and poisoning.
Killing pack animals like dingoes can fracture social groups, potentially altering their natural behaviour and interactions with other species. Future studies on predator interactions therefore need to consider the extent to which the animals are acting in response to human intervention.
If we want to benefit from the presence of top predators, we need to rethink our approach to management – especially where they are subjected to broad-scale control, as the dingo is in some parts of Australia.
Changing our relationship with top predators would not come without its challenges, but high extinction rates around the world (and especially in Australia) clearly indicate that we urgently need to change something. If this includes restoring top predators, then we need to think big.
Thomas Newsome receives funding from Deakin University, The University of Sydney, the National Geographic Society for Research and Exploration, Seattle City Lights, Washington Department of Fish and Wildlife, and Newmont Tanami Operations. He is Treasurer of the Australasian Wildlife Management Society and a member of the Australian Mammal Society and the Ecological Society of Australia.
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Once a week I record which species are drawn to the light, my first year of contributing data to the Garden Moth Scheme. This became a national project in 2007 and the fluctuations it shows are a valuable indicator of environmental change. The colour-coded Field Guide to the Moths of Great Britain and Ireland by Waring, Townsend and Lewington, covers 896 species, illustrated in their natural resting positions. These are the macro moths – there are a further 1,550 or so micro moths, which sometimes makes identification a challenge.
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The world would be better off if Trump withdraws from the Paris climate deal
The conventional wisdom that the United States should remain under the Paris Agreement is wrong. A US withdrawal would be the best outcome for international climate action.
With Trump set to decide on the matter after this week’s G7 meeting, his aides are split on the issue. Chief strategist Steve Bannon heads the faction pushing for an exit. Secretary of State and former ExxonMobil chief executive Rex Tillerson has argued for the US to retain a “seat at the table”.
It is within the president’s power to withdraw from the Paris Agreement and perhaps even the United Nations Framework Convention on Climate Change (UNFCCC), which has overseen global climate diplomacy for some 25 years.
In a commentary published in Nature Climate Change today, I argue that a US withdrawal would minimise risks and maximise opportunities for the climate community. Simply put: the US and the Trump administration can do more damage inside the agreement than outside it.
There are four key, interconnected risks related to US participation in the Paris Agreement: that the US will miss its emissions target; that it will cut climate finance; that it will cause a “domino” effect among other nations; and that it will impede the UN negotiations.
Money and emissions are all that matterThe first two risks are unaffected by withdrawal. The Paris Agreement doesn’t require the US to meet its current emissions reduction pledge, or to provide further climate finance to developing countries. The agreement is procedural, rather than binding; it requires a new, tougher climate pledge every five years, but actually hitting these targets isn’t mandatory.
The US will probably miss its climate target regardless. It would need more than just Obama’s Clean Power Plan to hit its goal of reducing emissions by 26-28% on 2005 levels by 2025. And now that Trump has decided to roll back those policies too, US emissions are set to increase through to 2025, rather than decrease.
The same goes for international climate funding, which will be cut under the “America First” budget plan. That includes funds previously earmarked for the Green Climate Fund, which has so far raised US$10 billion in climate aid. The US was to provide US$3 billion but has donated just US$1 billion so far. The remaining money is almost certainly not coming.
Domino effect?The third risk is the domino effect: that US actions could inspire others to delay climate action, renege on their targets, or withdraw. But there is little evidence to suggest that the US dropping out will trigger other nations to follow suit.
The closest historical parallel is the Kyoto Protocol, which the US signed but never ratified. When President George W. Bush announced that the US would not ratify the treaty, others rallied to the protocol’s aid and pushed through the Marrakech Accords in 2001, to strengthen Kyoto’s rules.
What’s more likely to cause a domino effect is US domestic behaviour, rather than any potential withdrawal from the Paris deal. Other countries are more likely to delay or free-ride on their pledges if they see the US miss its target, revealing how weak the Paris Agreement really is.
Paris has little aside from inspiring public pressure and long-term low-carbon investment patterns. Neither pressure nor the “investment signal” is likely to work if a renegade US shows that Paris is an empty global show-and-tell regime. Investors and the public are likely to lose faith in an agreement that can visibly do nothing to constrain a climate laggard.
The fourth risk is that the US will act as a spoiler in international climate talks. This requires membership. If the US remains in the agreement it will retain a veto in the negotiations.
The negotiations are at a crucial juncture. The so-called “Paris Rulebook”, which details how exactly the agreement will be fulfilled, is being negotiated, with plans for it to be adopted in 2018.
The US could use its voice and veto to water down the rules. It might even stall and overload negotiations by demanding amendments to the Paris Agreement, as Energy Secretary Rick Perry has suggested. A US that has credibly threatened to withdraw may have even more diplomatic clout going forward.
Considered in this light, giving the former head of ExxonMobil a “seat at the table” is a terrible idea.
New opportunitiesA US withdrawal, on the other hand, could create new opportunities, such as renewed European and Chinese leadership. In the wake of the 2016 US election, former French presidential nominee Nicholas Sarkozy raised the idea of applying a carbon tax of 1-3% on US imports. In a time of rising protectionist policies, particularly in the US, carbon border tariffs may become more politically palatable.
A US dropout would also be an ideal opportunity for a rising China to stamp its mark on an international issue. It would give both China and the European Union a chance to jump even further ahead of the US in the renewable energy markets of the future.
The EU previously showed leadership in the absence of the US to revive the Kyoto Protocol and forge ahead with renewable energy. This time Europe could do so with the support of another great power.
Such cooperation could take numerous forms. One simple way would be for the two to put forward a stronger joint climate pledge. This could be strengthened by uniting their respective carbon trading schemes and applying a common border carbon tariff.
Trade measures and an EU-China climate bloc will be far more effective than Paris ever could have been. Yet none of these possibilities is likely to become reality without the diplomatically drastic move of US withdrawal. On balance, it is clear that a US climate exit is preferable to remaining.
It is worth stressing here the difference between pulling out of the Paris Agreement and withdrawing from the UNFCCC. The latter is far more dramatic, and more likely to trigger a domino effect. It would also mean the US would no longer be legally bound to report on its emissions and actions to the international community. It would become a complete climate pariah.
A future president could easily rejoin Paris through an executive agreement. In contrast, re-ratifying the UNFCCC might require a vote in the US Senate, which has become more partisan and divided since the convention was first ratified in 1992. However, withdrawal from the UNFCCC would lessen the threat of US obstruction, as it would lose its veto in the wider negotiations and be even more politically ostracised.
Despite this, the same basic risk-opportunity calculus applies. The domino effect may be more likely, but overall a withdrawal is still preferable.
Participation is a red herringWanting the US to remain is a short-sighted, knee-jerk reaction. The international community should be much more worried about the real domestic actions of the US, rather than whether it is symbolically cooperating internationally.
The international community appears to be mortally afraid that the US will make the largely symbolic gesture of quitting Paris. Yet there was less concern when Trump rolled back domestic climate measures.
EU Climate Commissioner Miguel Arias Cañete recently stated that Paris allows for the continued use of fossil fuels and provides the flexibility for a “new US administration to chart its own path”.
Is this really a worthwhile message to send to the White House: that blatantly violating the purpose and spirit of the Paris Agreement is fine, as long as you are still cooperating on paper? It is disturbing that symbolism has apparently become more important than action.
Policy, not participation, needs to be the focus of criticism. Otherwise Paris will prove itself to be nothing more than a diplomatic fig leaf.
While Paris may be weak, international climate action can still be strong. The shock of Trump’s withdrawal could make international action stronger by allowing emboldened leadership to blossom elsewhere.
Luke Kemp has received research funding from the Australian and German governments.