Jeff McMahan doesn’t like carnivores. Not one bit. In a pair of controversial op-ed pieces in the New York Times “The Stone” forum, the Rutgers University philosopher has argued that our species has a moral duty to eradicate the world’s rapacious, pain-inflicting predators and replace them with specially-engineered herbivores with big doe-eyes and which smell like angel kisses.
To his credit, McMahan recognizes that the program of eradication and replacement he favors is not feasible. If were were to remove all carnivores in one fell swoop, he recognizes, we may well create “a Malthusian dystopia in the animal world, with higher birth rates among herbivores, overcrowding, and insufficient resources to sustain the larger populations.” Nevertheless, he still argues that the “peaceful” herbivores (as if browsers and grazers never fight, maim, and kill each other) of the world would be far better off if we did nothing while charismatic hunters such as the Amur tiger disappeared:
If we do nothing to preserve it, the Siberian tiger as a species may soon become extinct. The number of extant Siberian tigers has been low for a considerable period. Any ecological disruption occasioned by their dwindling numbers has largely already occurred or is already occurring. If their number in the wild declines from several hundred to zero, the impact of their disappearance on the ecology of the region will be almost negligible. Suppose, however, that we could repopulate their former wide-ranging habitat with as many Siberian tigers as there were during the period in which they flourished in their greatest numbers, and that that population could be sustained indefinitely. That would mean that herbivorous animals in the extensive repopulated area would again, and for the indefinite future, live in fear and that an incalculable number would die in terror and agony while being devoured by a tiger. In a case such as this, we may actually face the kind of dilemma I called attention to in my article, in which there is a conflict between the value of preserving existing species and the value of preventing suffering and early death for an enormously large number of animals.
Unfortunately for McMahan, he makes a rather poor armchair ecologist, and that is because he only considers two ecological components of his woolly hypothesis – carnivores and prey species. Carnivores kill prey species, something which McMahan finds morally reprehensible, but the ecological reach of a large carnivorous species extends beyond their consumption of prey species. Although it seems paradoxical, many predatory species inadvertently protect prey populations.
From textbooks to television documentaries, the deadly drama of predators and their prey is often depicted as a prime example of natural selection in action. What often goes unremarked upon is the relationship between apex predators, prey species, and second-tier predators. This latter group – the meat-eating middleclass technically termed “mesopredators” – is often composed of relatively small predators such as feral cats, raccoons, foxes, and rats. When an ecosystem is complete, top-predators influence the abundance and activity of mesopredators, but when top predators are removed the mesopredators proliferate and can do considerable damage to populations of prey species.
The influence unregulated mesopredators can have on an ecosystem is something which has only been recognized recently, but, by eliminating apex predators from many habitats, our species has been running ecological experiments relevant to this idea for over a century. The location of one such laboratory is in South Australia. Erected during the 1880’s, the Dingo Barrier Fence was constructed to keep the wild dogs out of fertile pasturelands used for sheep grazing, and this control measure has been supplemented with poisonous 1080 (sodium monofluoroacetate) baits. On the protected side of the fence, it is believed that dingoes have been all but eradicated, and their absence has been construed as a boon to the local wildlife as well as livestock.
Both the yellow-footed rock wallaby (Petrogale xanthopus) and malleefowl (Leipoa ocellata) live on refuges on the protected side of the dingo fence near the Flinders Range a bit north of the city of Adelaide. Between the presence of the fence, baiting for dingoes, and the extensive observation which has taken place at sites where these animals are present it was believed that they, too, had benefited from the absence of the dogs. The converse actually turns out to be true. As detailed in a Biological Conservation paper by Arian Wallach and co-authors published last year, a sparse population of dingoes has actually managed to survive behind the dingo fence, and their presence is closely associated with the habitats of the wallabies and birds.
When it comes to threats to native Australian animals, feral cats and red foxes are far more dangerous than dingoes, and the evidence collected by Wallach and co-authors is consistent with the hypothesis that the presence of an apex predator suppresses the activity of mesopredators. When they studied the abundance of dingoes, foxes, and cats in the area of Nantawarrinna station and the Vulkathunha -Gammon Ranges using tracks, scat, carcasses of prey animals, and sightings by local people, the researchers found that dingoes had as strong a presence in the wallaby habitats as in areas on the northern side of the dingo fence. There were dingo traces at each of the nine sites they investigated, and this evidence was bolstered by two sightings of dingoes made by the team and dingo howls heard at night. Both cats and foxes were very rare at each of the sites, and, based upon scats and carcasses, it was clear that the dingoes were eating kangaroos, goats, and other larger animals, not the rock wallabies.
A similar pattern was seen at the malleefowl sites scattered south of the Dingo Border Fence. These small pockets are often in shrublands near grazing areas for livestock, and even though the dingo has been declared to be entirely absent from these sites, Wallach and colleagues found that dingoes were present at all three malleefowl sites they investigated. At the malleefowl nests, however, fox traces were relatively more abundant, perhaps because malleefowl eggs are a prized food item for the problematic carnivores. Nevertheless, the observations of this and previous studies are consistent with the idea that malleefowl nests scent marked by dingoes are less likely to suffer predation by red foxes, hence dingoes provide a protective benefit through their territoriality. At nests closer to areas which are frequently poison baited, dingoes were rarer and predation by foxes has been more frequent. As the authors suggest, this may be the case at other sites where threatened species have hung on, and in the future field workers should make a greater effort to ascertain the presence or absence of dingoes in order to determine how predator control might be affecting endangered species.
The protection that dingoes have provided native prey species by controlling mesopredators and killing abundant large herbivores – which often hinder the recovery of threatened species through competition – can also be seen over time. In 2006 James Cook University scientists Christopher Johnson and Joanne Isaac, in collaboration with Australian National University’s Diana Fisher, published a report in the Proceedings of the Royal Society B which tracked the geographical relationship between dingos, threatened species, and species which have gone extinct since the time of European settlement.
Viewed from a historical perspective, the presence of dingoes was strongly associated with the persistence of native Australian animals. Even in areas where sheep and rabbits were present, if dingoes were common in the area then the native animals appeared to be better able to resist decline. (In areas where rabbits and sheep were present but dingoes were absent, on the other hand, native species did not fare nearly as well). This one piece of information represents a more complex ecological dynamic; dingoes suppress the abundance of foxes, which in turn reduces the threat to native species. (The relationship between dingoes and feral cats is less clear.) That this type of relationship might account for the pattern of extinction among Australia’s marsupials comes from the fact that dingoes were hunted and kept out of the fertile southern areas of the continent from about the time of European settlement. The distribution of dingoes today roughly represents what it has been like for the past 200 years, and the areas in which dingoes have been removed are the ones in which most of the native mammal extinctions have occurred. Despite the best efforts of humans, however, dingoes have persisted and provided unexpected benefits to local faunas, and as the authors state, “the dingo is a keystone species protecting mammal biodiversity in Australia and is the most significant constraint on the destructive power of exotic predators.” In order to preserve Australia’s wild animals, the dingo must be preserved, as well.
If the dingo was entirely eliminated from Australia, or if almost any apex predator was entirely extirpated, then prey species would suffer. To at least a minor extent, we have already run the experiment McMahan has proposed and found that in order to save prey species, we must save predators, too. The idea that we must so thoroughly regulate the wilderness – to the point where there is no longer any such thing as wilderness – is highly alarming. If we feel the compunction to kill all carnivores because they cause suffering, then should we also kill any herbivorous species which causes injury and suffering to members of its own kind? Should our goal be to eradicate all natural species and replace them with inoffensive creatures which do nothing but eat, shit, and multiply (presumably asexually since sexual reproduction systems breed competition for mates)? Would we be able to justify the destruction of the entire natural world in order to create a bland, sterile, and neutral global ecosystem in which the words “predator” and “prey” have no real meaning?
We already intervene in the wild – we have driven some species into extinction and ensured the extended survival of others – but, as parts of nature ourselves, I do not think we will be capable of the objective view that McMahan’s program of ecological and evolutionary reorganization would require. Nor should we try to play that role. The thought of abolishing nature in favor of a tightly-watched global factory in which no species is allowed to change or evolve beyond our concept or morality is simultaneously so ridiculous that it makes me want to laugh and so depressing that I want to cry. Predators may cause McMahan to feel uncomfortable, but I do not see them as morally good or bad. They simply exist as parts of still-evolving lineages, and if we are going to continue to meddle with their ecology at any level, the best thing we can do is try to understand the role of predators in nature.
Top image: Photo of a dingo (Canis lupus dingo) by Jarrod Amoore. From Wikipedia.
Johnson, C., Isaac, J., & Fisher, D. (2007). Rarity of a top predator triggers continent-wide collapse of mammal prey: dingoes and marsupials in Australia Proceedings of the Royal Society B: Biological Sciences, 274 (1608), 341-346 DOI: 10.1098/rspb.2006.3711
WALLACH, A., MURRAY, B., & ONEILL, A. (2009). Can threatened species survive where the top predator is absent? Biological Conservation, 142 (1), 43-52 DOI: 10.1016/j.biocon.2008.09.021