Editor’s Choice 56:12 – Do introduced apex predators suppress introduced mesopredators? The debate continues

Our December Editor’s Choice by Fancourt et al. indicates that the presence of dingoes in Australia is unlikely to suppress introduced feral cats. Associate Editor, Michael Bode, looks at the evidence in this new research and explains why he feels the debate around this topic is far from over.

In recent times, Australia has had one of the worst records of extinction in the world. Since the arrival of European colonists in 1788, at least 10% of its endemic mammalian fauna (34 species) has become extinct. Much of this loss can be attributed to the depredations of invasive cats and foxes, which continue to threaten with extinction 134 other species of mammals, as well as numerous birds, reptiles and amphibians.

Controlling the abundance of cats and foxes is not impossible, but it is very expensive. Despite its wealth of unique biodiversity, Australia has spent less on threatened species than comparable countries like the USA, and much less than would be needed to halt the current extinction crisis. If we want to reduce the effects of invasive predators on Australia’s native wildlife, we need to find a way to do it ‘on the cheap’. A vocal cohort of conservation scientists suggest that dingoes are one way to achieve this.

feral cat d61_2_0158 - Joe Scanlan
Feral cat by Joe Scanlan

Dingoes are a species of native Australian dog and have lived on the continent for at least 3,500 years. Because they are an apex predator, pro-dingo conservation scientists argue that the species can mitigate the impacts of cats and foxes (so-called ‘mesopredators’) on native wildlife. The argument is theoretically compelling – dingoes are known to harass and kill both foxes and cats, and their presence could therefore affect the activities and reduce the abundance of invasive predators. Substantial conservation gains could be achieved, these scientists argue, if we simply stopped lethal control of dingoes across Australia’s farm and rangelands. A host of scientific publications support this hypothesis, justifying the benefits theoretically, and measuring them empirically.

However, a counter-host of scientific publications cast doubt on the mesopredator suppression hypothesis. Using different approaches, assumptions, and datasets, these papers draw the opposite conclusion: despite evidence of dingo predation and interference, the presence of this apex predator has no significant negative effect on cats and foxes, and no significant positive effect on the abundance of the small marsupials. These counter-culturalists have their own, equally-plausible theoretical arguments: dingoes are predators, and so their indirect benefits for native marsupials (through mesopredator suppression) are just as likely to be out-weighed by their direct negative impacts on those native species. This Editor’s Choice by Fancourt and colleagues adds to this evidence base. The authors analyse intensive camera-trapping data from sites in central Queensland and conclude that there is no evidence that dingoes suppress the abundance, or alter the behaviour of cats. However, despite its methodological rigour and multifaceted analyses (the paper investigates the effects of dingoes on cat abundance, as well as on the spatiotemporal distribution of cats), I believe this publication will not definitively end the debate. Instead, it adds one more quantum of evidence to the counter-argument.

3D7A0723 - Ben Allen
Dingo by Ben Allen


It is unlikely that the debate about the net effects of dingoes on threatened Australian marsupials will be resolved soon. The ongoing online discussion of Fancourt and colleagues’ article (see, for example, Twitter threads here and here) quickly reveals the key factors that challenge consensus. First, although the evidence contained in this paper is empirically strong, the results are from one location in central Queensland, and applied ecology can be highly context-specific. Perhaps both sides of the debate are correct, just in different locations? Moreover, the response variables at the heart of this question – the spatiotemporal distribution of mesopredators – are incredibly difficult to measure accurately, particularly using methods like camera traps. Significant differences between sites with and without dingoes can therefore be very difficult to identify, even when they exist. Finally, the dingo-mesopredator-marsupial ecosystem is a web of indirect and direct interactions, where causality is hard to attribute and it is very difficult to predict the consequences of an intervention.

In observing the debate that followed the publication of this thought-provoking article, it occurs to me that, despite the evidence it presents, we are no closer to consensus than we were before, and existing opinions may still prevail. The role of dingoes in the suppression of mesopredators will continue to be hotly contested because – in the short-term at least – the question goes beyond the strictly scientific.

In an ideal world, scientific progress is a process of evidence accumulation and persuasion. Scientists conditionally support the theories that have the strongest empirical support but change their minds when the weight of evidence falsifies an existing hypothesis, or suggests a superior explanation. In the real world, things are more complicated. There’s an old saying in physics that’s been variously attributed to Max Planck, Richard Feynman, and Albert Einstein – basically every famous physicist from the early quantum era: ‘Theories aren’t disproved; old theorists die’.

Science is a human endeavour. When two theories are in conflict, scientists make up their minds on the basis of the evidence presented to them. However, their decision is also influenced by their preconceptions, their vested interests, their value systems, and their tribal allegiances. These factors make it hard for individuals to change their positions and encouraging them to do so is not necessarily as straightforward as the publication of a paper.

The effects and influence of Fancourt et al., as a consequence, will likely not be felt among all of today’s conservation scientists. Having spent the past few weeks reading journal articles, opinion pieces, and Twitter posts on both sides of the debate, it’s not clear to me that either faction will be persuaded by another experimental study. But that’s OK, because I think the impacts of these experiments will be apparent in the next generation of applied ecologists. When this new cohort comes to form their applied ecological opinions, they will consider anew the weight of evidence on both sides of the debate. In doing so they will find this paper to be a strong voice against the instrumental value of apex predation in ecosystem management.

The full Editor’s Choice article, Do introduced apex predators suppress introduced mesopredators? A multiscale spatiotemporal study of dingoes and feral cats in Australia suggests not, is free to read for a limited time in Journal of Applied Ecology.

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