The Enemy of My Enemy is My Friend: The Case for Native Predator Ecosystem Recovery

The reintroduction of Wolves (Canis lupus) into Yellowstone National Park is regarded as one of the great ecological success stories in modern history: a risky experiment that not only saw the recovery of various native species but a process that literally changed the landscape itself (Ritchie et al, 2012).

Is it now Australia’s turn?

Let’s go back a step

It’s hard to think of an endangered terrestrial vertebrate that isn’t threatened by the feral cat (Felis catus) and European fox (Vulpes vulpes)*. Yet when control of these predators is discussed, even at an asset protection level, researchers and land managers alike begin to naval gaze: no sustainable, practical, long term approach has yet been devised.

Even controls that have limited success, such as poison baiting and shooting/trapping, are rife with complications ranging from high costs to off-target damage. Thus feral mesopredators are given free reign across much of Australia, with the functional absence of Apex predators leading to a cascade of change across the food web. To add insult to injury, the control of one higher level vertebrate predator (such as foxes) can boost the numbers of a lower-level predator (such as cats); a process known as the mesopredator release hypothesis (Fancourt et al, 2015).

To replicate Yellowstone with Dingoes (Canis lupus dingo) would be unfeasible and unpalatable across much of Australia. Dingoes kill livestock, breed with wild dogs and require large home ranges- qualities that do not go well with protected areas that border on farmland and urban dwellings. If only there was another native animal that could act as an ecological surrogate for Dingoes…

Cue Tasmanian Devils (Sarcophilus harrisii)

Tasmanian Devils (heron referred to as Devils) were present on the mainland for thousands of years, but a combination of increased human densities, climate change and the arrival of dingoes around 5000 years ago meant that only populations in Tasmania  survived (Hunter et al, 2015).
Interestingly, you may have noticed that Tasmania is the last refuge for a range of native vertebrates extinct or near extinct on the mainland (Bettongs, Eastern Quolls etc) and it has been suggested that this may partially be because Devils have prevented feral predators from gaining a functional foothold (Figure 1).

Dingo v Fox map

Fig 1. Distribution of foxes is hashed with distribution of dingoes in shades of grey. Note the relative functional absence of both species in Tasmania (M. Letnic et al, 2011)

Thus, it has been proposed that Devils could be reintroduced onto the mainland to help restore trophic balance while also establishing an insurance population free from Devil Facial Tumour Disease: a win-win!
But where to trial the re-wilding? If only there was somewhere close to Tasmania with a similar climate, vegetation and landscape but still large enough for an independent
population…

Fig 2. Wilsons Prom: the most southern point of the Australian mainland and an excellent starting point for Devil reintroduction

 

 

I present Wilson’s Promontory: 50 000 hectares of IUCN category II National Park, rich in forest, threatened wildlife and feral mesopredators, with the luxury of being a peninsular should exclusion fencing be deemed necessary for a large scale trial (Figure 2).

 

 

 

A Point of Clarification (i.e. the Devil’s in the Detail)

If you’re thinking “But Devils are mesopredators, not apex predators…how can they effectively control other predators at, or close to, their trophic level?” you are not alone: the myriad of other journal articles and blogs proposing Devil introduction are often met with the same criticism (Fancourt & Mooney, 2016).

Let’s not pretend for a moment that Devils, which move with all the composure and grace of a salivating, mini tornado**, will be wiping out wily foxes and cunning cats. With the exception of cubs and kittens, it’s unlikely they would even try but the point is moot: it’s not about hunting, it’s about hostility. After all, the key success in Yellowstone was large herbivores avoiding rivers to evade predation, not simply the decline in their numbers i.e. “behaviour can be just as important as abundance” (Ritchie et al, 2012).

So could Devils have this same avoidance impact on vertebrate pests? Perhaps so: research from the University of Tasmania (2015) shows that in areas with Devils, feral cats, who are normally a nocturnal predator, hunt during the day instead to avoid disruption from Devils (Figure 3). Furthermore, modelling (using Fuzzy Cognitive Mapping) suggests that in areas like Wilsons Promontory, Devil reintroduction “would have cascading effects similar to but weaker than dingoes…[leading to] lower abundances of introduced mesopredators” (Figure 4).

screen-shot-2016-10-02-at-4-33-30-pm

Fig 3. Cat activity times (blue line) compared with spotlight survey times (grey shading). Nocturnal detection rates increase in areas with longer presence of Devil Facial Tumour Disease              (Fancourt, 2015)

screen-shot-2016-10-02-at-9-46-32-pm

Fig 4. a. Species distribution model of potential Devil distribution on the mainland under the current climate scenario; b. distribution of the Dingo and hybrids (Hunter et al, 2015)

Whether it’s through direct predation, avoidance behaviour or simply resource competition, Devils are bad news for feral mesopredators. If the results from Tasmania could be replicated in Wilsons Promontory in addition to traditional vertebrate pest control it could provide a colossal relief to threatened species, particularly nocturnal vertebrates and surface nesting/ roosting birds.

But let’s not oversimplify. Correlation does not equal causation- predator interaction is incredibly complex and there is a risk that adding another predator to an already stressed food web could have a negative effect on threatened species (Figure 5). These issues are not show-stoppers, they simply highlight the need for experiments and trials.

Fig 5. Complex food webs already strained by introduced predators may be further distrupted by an additional native predator (Robley et al, 2004)

Time for a Paradigm Shift

It is exceptionally rare that a re-wilding opportunity presents itself with the potential to boost the dwindling population of the reintroduced species while also assisting with the conservation of native biota in the release area- that’s why the case for the reintroduction of Devils should be seriously considered. Let’s look at the big picture too: there is significant potential to promote ecosystem recovery through the re-wilding of other apex predators, including Dingoes, Komodo Dragons and Raptors (Hutchinson, 2014).

Yes, native predator competition is not a silver bullet but rather a gentle tipping of the scales in our favour. And yes, these are likely to be risky and expensive exercises conducted in risk averse, competitively fiscal environments. But in a world of scarce funding for threatened species protection, surely merit should be given to projects with long term benefits for multiple threatened species?

To the advocates, let’s be realistic and proceed with caution: the complexity, unknowns and risks mean that treading carefully is imperative.

To the nay-sayers, I’ll remind you that reintroducing Wolves into Yellowstone was once just a day-dream too.

 

Nicholas Daines, u4423873

*well, yes, except Cassowaries…for obvious reasons

**Looney Tunes reference for any confused readers https://www.youtube.com/watch?v=c54SvkgQ04A

 

References

Fancourt, B., Hawkins, C., Cameron, E., Jones, M. & Nicol, S. (2015). Devil Declines and Catastrophic Cascades: Is Mesopredator Release of Feral Cats Inhibiting Recovery of the Eastern Quoll? PLoS ONE, 10, e0119303.

Fancourt, B. & Mooney, N. (2016). Tasmanian devils are likely a blunt instrument: a comment on Hunter et al. Biological Conservation, 27, pp50-55.

Hunter, D.O., Britz, T., Jones, M. & Letnic, M. (2015). Reintroduction of Tasmanian devils to mainland Australia can restore top-down control in ecosystems where dingoes have been extirpated. Biological Conservation, 191, pp428–435.

Hutchinson, N. (2014). “Rewilding fragile ecosystems.” Geodate 27.2: 8.

Letnic, M., Greenville, A., Denny, E., Dickman, C., Tischler, M., Gordon, C. & Koch, F. (2011). Does a top predator suppress the abundance of an invasive mesopredator at a continental scale? Global Ecology and Biogeography, 20, pp343–353.

Ritchie, E.G.Elmhagen, B.Glen, A.S.Letnic, M.Ludwig, G. & McDonald, R.A. (2012). Ecosystem restoration with teeth: what role for predators? Trends in Ecology & Evolution27, pp265271.

Robley, A., Reddiex, B., Arthur, T., Pech, R. & Forsyth, D. (2004). Interactions between Feral Cats, Foxes, Native Carnivores, and Rabbits in Australia. Melbourne: Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, pp1-34.

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About Biodiversity Conservation Blog

I am an Associate Professor at The Australian National University and convene a (very awesome) course called Biodiversity Conservation. Myself and students in the course contribute to this blog.
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One Response to The Enemy of My Enemy is My Friend: The Case for Native Predator Ecosystem Recovery

  1. Really interesting Nick. I wonder if this might work in the ACT to enhance survival of the eastern bettong beyond the fence at Mulligans? Phil

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