Image: monoculture of buffel grass (non-native) and red gum (native), by A. Wallach.

Eleventh on our Black Dog Series is dedicated to all plants on the move, and how the conservation of apex predators helps promote diverse plant communities. Plants do sometimes form monocultures. Some of these may be flammable, irritating and thorny. Monocultures are formed because many of the local plants are unable to flourish under the extreme disturbances to the area. 

Introduced plants rarely ‘outcompete’ native plants. When we overgraze with livestock, kill predators, burn and clear, fewer plant species may survive. Those that do well have special adaptations to high disturbance regimes. High grazing pressure may facilitate communities dominated by less palatable plants, some of which are introduced. 

Plant diversity forms a ‘biotic resistance’ that limits competitive dominance by any one species. Even in systems in which introduced plants are competitively superior, coexistence can develop through the complexity of interactions that form ecosystems. Large predators can help restore a more diverse plant community in which monocultures are less likely to form. 

Weeding does not help promote native plants, but weeds do. There are many examples of native plants and animals forming dependencies on introduced plants. For instance, across its introduced range the lantana shrub (Lantana camara) provides a broad variety of benefits by promoting the regeneration of some native plant species, improving soil retention, and providing habitat for native animals, along with a range of medical uses and opportunities for local economies. 

What have the weeds ever done for us? 

Apart from increasing primary productivity… sequestering carbon… feeding livestock… feeding wild herbivores… sheltering small animals… sheltering large animals… providing food, medicine and employment to humans… stabilising, aerating and improving soil… promoting native plants… and improving overall biodiversity…..?

By Arian Wallach

Image: Hidden beauty of cane toads from news.com.au

Tenth on our Black Dog Series is the most honourable and distinguished of ferals – the cane toad (Bufo marinus). Blamed for far too much, and hailed for far too little, these amphibians are now an integral part of Australia’s beauty. 

Their gland secretions are toxic to many predators, and some naïve populations have locally declined. They have never caused extinctions however, and although declines can be sharp, they tend to be temporary.

Life is remarkably adaptable, and toads have become an engine of evolution. Some native snakes have undergone rapid adaptation to cane toads, reducing the size of their mouths relative to the size of their bodies, so that they are now able to tolerate the amount of toxin ingested. Other species, including several native birds, have learned how to hunt cane toads successfully by avoiding the toxic glands and eating the rest. And yet others simply learn to avoid them, and hunt someone else. These extraordinary examples of rapid evolution have resulted in the recovery of native predator populations from initial declines. Human efforts to control toads have not been helpful.

Toads are opportunistic predators that can help regulate potentially irruptive invertebrates and small vertebrates. As prey, they benefit a range of predators once the adaptation to their toxin occurs. But like any species, ecological benefits come from sustainable densities, and thus biodiversity increases when the predators of cane toads are abundant. And this is where the dingo can help. 

Large predators regulate species both directly by hunting them, and indirectly by promoting the diversity of their predators and competitors. When dingoes suppress mesopredators (e.g. foxes and cats) and herbivores (e.g. rabbits and kangaroos), they indirectly benefit the populations of a variety of other species. Some of which are toad predators. 

By Arian Wallach

Image: sambar deer from http://austdeer.com.au

Eighth on our Black Dog Series are six species of deer that have established in Australia. Three of Australia’s deer species are threatened with extinction in their native ranges: sambar (Rusa unicolor), Javan rusa (Rusa timorensis) and hog deer (Hyelaphus porcinus). 

All six deer species have coevolved with large carnivores that prey on them, and their ecological roles are strongly influenced by the presence (or absence) of apex predators. Human hunting can have suppressive effects on some deer species in some situations, but these effects do not mimic those generated by apex predators. Apex predators do more than kill deer, they communicate with them. Deer respond to predators through stress responses that affect their reproduction, increased vigilance that affects their nutrition, and by moving into areas that provide safe havens. The effects of dingoes on deer are likely to be similarly substantive, but these have yet to be studied.

Unlike most introduced species, deer are provided with some legal protection thanks to hunting organizations that advocate for their management as a resource (‘game animals’) rather than as a pest. While this provides many benefits (including improved deer welfare), we argue that deer should also be regarded for their intrinsic and ecological values. Importantly, hunting organizations overseas are often powerful lobby groups, alongside farmers, advocating for predator control. Australian hunters have the opportunity to develop an evolved ethic for the treatment of deer and their predators. 

As ecologists, we call for a greater consideration of the ecological roles deer now play in Australia’s modern ecosystems, and the trophic effects of dingoes on their populations. For example, one study found that hog deer provide a major ecological service as seed dispersers for both native and exotic plants in Australia. 

As conservationists, we call for caution at trying to eradicate species from their introduced ranges when their native ranges are jeopardized. In particular since deer eradication programs have not provided the anticipated benefits to native species. 

Finally, as people who also value the welfare of individuals, we call for compassion for deer that call Australia home.

By Arian Wallach

Image: wild goat in the northern Flinders Ranges, South Australia, by A. Wallach

Goats (Capra aegagrus) are rewilding across Australia, embedding themselves into the ecology of cliffs and gorges, and by doing so are recovering their ancestral population that are threatened with extinction. The seventh in our Black Dog Series plays an ecological function as a browser - a consumer of tree and shrub vegetation. Browsers provide important ecological services by opening up thickets that otherwise become impenetrable. At sustainable densities they help create mosaics of open and closed vegetation. The open patches they create provide the conditions needed for grasses and forbs to thrive, which in turn benefit a multitude of other (native) species. 

Like any other herbivore, their beneficial browsing can turn into overgrazing damage when their populations irrupt. One of the most obvious signs of dingo persecution is a tree line, in which the trees are grazed up to the highest point that the goats can reach. It is under such conditions that wild goats are typically studied. 

We conducted research on Aboriginal land in the northern Flinders Ranges, South Australia, where dingoes had been left unharmed for a few years. Within one of the gorges was a hidden spring where wild goats and other water-dependent animals came to drink. This was the prime hunting ground for dingoes, evident by over fifty dingo kills - and in turn - lush green vegetation at the water. At night we heard the dingoes howl. We returned to the same site a year later following a poison-baiting campaign. We could feel the difference in the dust. The hidden spring was bare and trampled, goat droppings covered everything, and the nights were silent.

Freeing dingoes from persecution would drive the wild goats to the cliffs, not to extinction. And under these conditions wild goats are a sight to behold.

Image: wild bull in the Simpson Desert, by A. Wallach

If you want to see rewilding in action, come to Australia where the wild cattle (Bos taurus) roam, the fifth species on our Black Dog Series. The ancestor of cattle, the auroch (B. primigenius), is sadly extinct, but is reincarnating in the form of wild (feral) cattle. Although domestic and wild cattle are the same species, there are many differences between them.

The difference lies in demography and management. Because humans do not manage wild cattle, their populations contain 50% males, all males are bulls, and the age structure is not geared towards the most reproductively active part of a cow’s life. In such a herd, every calf is precious. Every calf lost a tragedy. The effects of dingoes are therefore likely to differ significantly between cattle managed for maximum reproduction and those that are wild.

In our previous post on wild camels, we discussed how the dingo, a relatively small apex predator, could influence megaherbivore. The same goes for wild cattle. For example, the wild cattle gracing our Simpson Desert study site, behave very differently to the domestic cattle we managed on Evelyn Downs, a predator-friendly cattle station.  

The wild cattle were never observed hanging around water, although on some nights the bulls congregated at the water for a few hours to roar and proclaim their territorial might. Some nights the bull-roars were louder than the dingo-howls. By contrast, the cows and calves were always shy: coming in to drink at night and leaving quickly moving, back out into the sand dunes as far as 40 km from water. Who were they afraid of? Humans? Dingoes? Fighting bulls? Perhaps all three. Whatever the reason, our experimental water has thus far remained lush with vegetation even though the nearest water is over 50 km away and the summers are ruthlessly hot. 

We have been studying dingo-wild cattle interactions for five years thus far. The investigation continues! Stay tuned.

By Arian Wallach

Image: wild boar mother with piglet by Laurent Geslin, from arkive.org

Wild boar (Sus scrofa), sixth in our Black Dog Series, is a keystone ecosystem engineer that can influence a variety of ecological properties through rooting activity and as predators and prey. Wild boar primarily eat plants and share much in common with the ecological role of bears. They help disperse seeds, affect nutrient cycles that benefit trees, and can increase plant species and habitat richness when their densities are sustainable. Wild boar are also effective predators on a variety of prey – from earthworms to fawns – although their influence on prey populations is not well understood.

As they spread across the globe (both independently and with human assistance), they have formed symbiotic relationships with a variety of native species. For example, naturalised wild boar have formed symbiotic feeding-cleaning relationships with native birds that consume their ectoparasites. Boar-human symbiosis has a history dating back thousands of years, with evidence of domesticated boar (pigs) in Oceania, including Papua New Guinea, appearing between 10,000 and 3,000 years ago.

There is little known difference between the ecologies of wild boar in their native and introduced ranges, and their populations can irrupt in both locales in the absence of large predators. In their native range of Eurasia, wolves and tigers are important predators. In North America where they were introduced, wolves, cougars, black bears, coyotes and bobcats are boar predators, and in Australia dingoes limit their densities. 

Wild boar quickly form complex interactions across the food web, forming ecological links with an immense variety of organisms from invertebrates, forbs, trees, small mammals, birds, reptiles, soil chemistry and to large predators. Activities aimed at boar control and eradication may therefore backfire with unintended consequences. A better option is to allow the predators of wild boar, such as dingoes, to thrive.

By Arian Wallach

Image: Simpson Desert camels, by A. Wallach

Fourth on our Black Dog Series is the largest, but least known, of Australia’s naturalised species – the dromedary camel (Camelus dromedarius). Species must often shift their range when the environment changes, and it seems clear that the camel does not have a home to go back to. Dromedaries are now extinct in their native range. 

But where exactly is their native range? 
Where, as Ken Thompson writes, do camels belong?

The camel family (Camelids) evolved in North America 40 millions years ago and only much later spread to South America and to Asia. They survived in North America until they went extinct only 8,000 years ago. Should we then send the camels back to their evolutionary roots in the US? Or how about South America, which retains the highest diversity of camelids (e.g. llama)? Or we could sell them into 'slavery' in the Middle East. Alternatively we could ship them off to Mongolia to join what is left of their cousins, a tiny herd of critically endangered Bactrian camels (C. bactrianus)? 

Our preference is to embrace our new ecology and rejoice that wild dromedaries have survived – wild and free – in the deserts of Australia. 

Australia lost much of its megafauna during the Pleistocene (past 50,000 years). It is plausible that the camel is now assuming some of the missing ecological functions of these lost giants. Like all species, limiting population density can be the key difference between harm and asset. We are now testing whether providing protection for dingoes can help regulate camels.

How can a predator the size of a dingo possibly affect a herbivore the size of a camel? Apex predators affect their prey not only by killing them but also by scaring them away from certain areas. Dingoes are a threat to baby camels and so the mothers have to keep them safe from dingoes until they are large enough. And this can make all the difference.

By Arian Wallach

Australia has helped rescue an endangered species from possible extinction, albeit unintentionally. That species, the third on our Black Dog Series, is the European rabbit (Oryctolagus cuniculus), listed as Near Threatened by the IUCN. 

Reviled by too many for too long, for causing "land degradation", rabbits form an integral part of Australia’s modern ecology. When humans kill their predators, rabbit numbers can increase and plant cover can decrease. But when their predators, particularly dingoes and foxes, are left alone, rabbit densities are contained and they perform important ecological functions as prey, herbivore and ecological engineer.

Everybody loves to eat rabbits. Dingoes, foxes, cats, raptures, monitor lizards and other predators (including humans) feast on them. If wedge-tailed eagles were asked whether they want Australia free of rabbits, they would undoubtedly vote “no”! A variety of species find shade and safety in rabbit burrows, and seeds get trapped in their diggings. When their densities are moderated they benefit plants by symbiotic plant-herbivore interactions such as spreading seeds, soil fertilisation and aeration, and pruning. 

Eradicating rabbits is thankfully impossible on Australia’s mainland but sadly has been done on some offshore islands. The ecological costs of rabbit eradication was most strikingly demonstrated in Britain where they were introduced and considered a "pest" (European rabbits are native to the Iberian Peninsula, not to Britain). The spread of myxomatosis into Britain hit the rabbits hard, with unexpected consequences including the extinction of the large blue butterfly (Maculinea arion). 

Australia too can be grateful for the rabbit.

By Arian Wallach

Image: Australian wildcat in the desert of southern Lake Eyre, by A. Wallach

The Australian wildcat (Felis catus) is second on our Black Dog Series. Like foxes, cats can drive population declines and even extinctions of their prey in some – but certainly not all – circumstances. 

The ecological contexts that drive hyper-predation by cats are primarily 
(1) dingo persecution, (2) absence of permanent water, and (3) intense fire and grazing pressure.  

Cats avoid dingoes in both time and space. In the presence of dingoes cats will avoid hunting at dawn, because that is when dingoes are active. Cats also avoid areas frequented by dingoes, such as water points. Shutting down artificial water points therefore indirectly benefits cats. Loss of vegetation cover (through fire and grazing) exposes small mammals to cat predation and compounds their effects. 

Cats do provide important benefits to biodiversity, and this was most clearly demonstrated on Macquarie Island following a cat eradication program that severely backfired. Once cats were removed, rabbits irrupted, causing large-scale vegetation loss and erosion. Both native and introduced rodents will similarly irrupt and cause harm when mesopredators, such as cats, are absent. 

To help native prey coexist with cats we need to stop killing dingoes, reduce livestock grazing pressure and reduce intense wildfires. 

By Arian Wallach

Image: Red fox in South Australia, courtesy of Les Peters

First on the Black Dog Series is by far the Most Wanted of non-native species: the red fox (Vulpes vulpes). Foxes are considered the major drivers of Australia’s mammalian extinction crisis, but do they really deserve such a harsh reputation? Not really. 

The ecological influence of foxes is context dependent. Dingo persecution, fire, land clearing, habitat fragmentation and grazing all pave the way for fox population irruptions and to conditions that make small mammals vulnerable to predation. Dingoes, in particular, are highly effective at limiting fox populations. In fact, the very method used to control foxes - 1080 poison baiting - ironically causes fox population irruptions, because 1080 kills dingoes too. Dingoes do not eradicate foxes, but they do limit their density, restrict their movement and change their behaviour. 

What are the ecological benefits of foxes when their densities are sustainable? Well, the same benefit they provide in their native range: they help limit populations of smaller predators and prey. Australian islands with foxes have had fewer extinctions than those without because they help suppress rats. Killing foxes also leads to irruptions of cats and rabbits, to the detriment of small native mammals and plants. 

Killing foxes has failed to suppress fox populations, it does not help recover native prey, nor does it reduce fox predation on lambs. The conservation of dingoes, and the protection of habitat, are the most powerful ways to help foxes and native prey coexist.

By Arian Wallach