Dogs: Why canids rule the world
Sociality, adaptability, loyalty: the traits that endear dogs to us also underpin the extraordinary success of their wild cousins. Steve Harris reveals how canids rose to global domination.
A red fox in the snow in Abashiri Shiretoko National Park, Hokkaido Island, Japan © Wolfgang Kaehler / LightRocket / Getty
What is the world's most widely distributed land mammal? Take a guess. A rodent, perhaps - possibly the brown rat or house mouse?
Not even close. Until recently, this accolade belonged to the grey wolf. When its numbers plummeted, succumbing to heavy persecution by humans, the crown passed to the red fox, currently found in 83 countries and on five continents.
This species continues to spread both northwards, taking advantage of climatic changes, and into deserts and other inhospitable areas where human populations are now increasing.
Throughout its range, the red fox capitalises on the waste, habitat changes and farming activities that are associated with human communities. So as our numbers continue to rise inexorably, we can also expect the fox to expand its range.
And what do wolves and foxes have in common? They are both canids, members of the Canidae – the dog family, one of the most successful groups of mammals in the world.
It’s a dog-aid-dog world
Canids first appeared about 40 million years ago in North America. Early in their history, a key behavioural trait emerged: the pair bond.
Males provision their lactating partners, then also provide for the developing young. This support is critical to their success: it enables mothers to rear large litters – typically up to eight pups, though some species can raise double this number.
In contrast, cats (felids) don’t have this pair bond: the male does not support the female, who must rear her kittens – generally only two or three at a time – unaided.
Big litters help canids to survive heavy persecution: typically, they can withstand mortality rates of 70 per cent or higher every year without a decline in population. Cats, with fewer offspring, are much more vulnerable to hunting pressures.
The other great benefit of the pair bond is that it has enabled the canids to develop complex social systems. Even species such as the red fox, which were once thought to be mostly solitary, can form very big social groups: the largest recorded comprised 10 adults.
Generally, these extended families still only produce one, or sometimes two, litters of cubs, with the adults all helping to rear them.
This allo-parental care takes many forms: all of the group’s adults bring food to the pups to varying extents – females may even lactate spontaneously to help suckle the dominant female’s pups. These behaviours are all believed to contribute to the successful rearing of large litters.
Unlike wolves and other species that hunt in packs, red foxes still forage alone; they may spend just a few minutes with other group members each day. But like many other canids, their social life is extremely flexible and adapts rapidly to changing circumstances, as well as different habitats.
After sarcoptic mange caused numbers to crash in 1994, foxes in Bristol adopted very different social systems, even though their habitat hadn’t changed. When the population was at its lowest, families consisted of single females with pups, or breeding pairs with very large territories.
Then, as numbers recovered over the next 15 years, social groups grew to become small associations of often one male and two females, then several adults of both sexes living in small territories: the pre-mange social system.
Mating behaviour also changed in tandem with these factors, from monogamous pair bonds in sparse populations to increased rates of intergroup copulations at high densities. The social systems of other successful canids – coyotes, wolves and jackals – show similar flexibility.
Strength in numbers
Clearly, greater numbers are beneficial: bigger wolf packs can hunt more substantial prey, and larger groups of African wild dogs are better at defending their kills from hyenas.
These flexible, and highly adaptable, social structures call for a complex system of communication. So canids employ a diverse array of other social behaviours including a range of body postures to signal subtle changes in dominance and submission.
They use varied vocalisations, too; red foxes have 20 different calls. Scent marks are also incredibly complex: different chemical signatures identify each animal’s sex, health, status and reproductive condition. And we still have a great deal more to learn about the intricacies of their social organisation.
African wild dogs live in large packs © Wolfgang Kaehler / LightRocket / Getty
Long in the tooth – and jaw
Canids aren’t fussy eaters – and that’s another factor in their global success. Most are generalists, feeding on a variety of vertebrates, invertebrates and plants; this dietary flexibility has enabled them to colonise a wide range of environments.
Smaller species such as the fennec fox (weighing as little as 1kg) can exploit resource-poor habitats such as deserts. Red foxes have colonised more than 140 cities around the world, and coyotes are common in many North American towns.
For the same reason, canids are able to live in areas where the types of food available vary widely throughout the year. For instance, in winter Arctic foxes often spend long periods out on the sea ice looking for the remains of polar-bear kills and other dead marine mammals; during the summer they hunt lemmings and birds on land.
Those species that are more dependent on large prey have been less able to survive change – for instance, the dire wolf, which disappeared 10,000 years ago. Specialists with limited ranges, such as the Ethiopian wolf, island fox and bush dog, are also at risk.
The real generalists, both in terms of their diet and the habitats they occupy, are usually extremely common: red foxes, coyotes and black-backed jackals thrive despite widespread persecution.
You are what you eat
A key factor in the canids’ ability to exploit a wide range of food types is their lack of a highly specialised dentition: they have different kinds of teeth to tackle just about any meal.
Cats, in contrast, have large canines and carnassials to kill and chew their prey; most other teeth are vestigial or have been lost – they are not required for their more specialist diets. So cats typically have 30 teeth, dogs 42.
Differences in prey are also reflected in the jaws and skull: canid species that specialise in hunting small animals have long, narrow jaws adapted to close fast, rather than bite with great power; their skulls are relatively weak.
Those that hunt large, dangerous animals have short, broad jaws, the most powerful bites and very strong skulls to enable them to survive struggles with big prey.
Cats typically have 30 teeth © TASS / Getty
Brain and brawn
Another key aspect of the canids’ ability to survive adverse situations is their perceived intelligence. In 1906 the US Bureau of Biological Survey was set the task of clearing grey wolves from cattle ranges. Large numbers of professional trappers were recruited, and by the 1950s the predators were largely exterminated in the contiguous 48 states.
Despite widespread trapping, poisoning and shooting, some individuals evaded their persecutors.In the process they became local legends, earning names such as ‘Old Three Toes’ (he lost one digit escaping from a trap in South Dakota).
And just look at how wolves have flourished following their reintroduction to Yellowstone National Park in 1995, rapidly learning to hunt new prey such as bison.
On the move
Canids are also highly mobile; with long limbs and lithe bodies, they are suited to travelling long distances in search of food. Packs of African wild dogs can have territories spanning several thousand square kilometres, while Arctic foxes may wander many thousands of kilometres in search of prey during the long Arctic winters.
Mobility also enables canids to disperse rapidly to colonise new habitats – yet another characteristic that enables them to thrive when times are tough. In Britain, for instance, if gamekeepers kill all of the foxes in their local area, these are rapidly replaced by immigrants that have travelled long distances in their search for a vacant territory.
It is hardly surprising that a canid – the wolf – was the first animal to be domesticated, probably in southern China less than 16,300 years ago. This coincided with the beginning of rice farming, so may first have been achieved by sedentary hunter-gatherers or early farmers.
Genetic data shows that many wolves were tamed independently at different times, suggesting that domesticating them was an important cultural trait.
In the intervening period, particularly the past few hundred years, selective breeding has produced nearly 500 varieties ranging in size from Chihuahuas to the likes of great Danes and wolfhounds; the biggest dog on record was an English mastiff called Zorba, who weighed in at 156kg in 1989.
Selective breeding has produced a range of domestic dog breeds © Barcroft Images / Barcroft Media / Getty
Who's the boss?
The adaptability of their wild ancestors is reflected in the diverse roles of domestic dogs: some are designated as companions, while others are bred for use in various types of hunting, guarding, fighting, locating drugs and weapons, and so on. In contrast, it is hard to be sure that domestic cats can even really be described as ‘companion’ animals.
Wolves are extremely adept at reading body language. Having co-existed closely with humans for thousands of years, it is hardly surprising that their domesticated descendants have become remarkably good at recognising what makes us happy – and acting accordingly.
The dog rushes to greet its owner, who is convinced that Fido is crazy about him or her. The pet gets exactly what it wants: lavish care and lots of food. But just who is manipulating who?
MAN'S BEST FRIEND?
Our relationship with domestic dogs is more complex than a simple whistle-and-fetch dynamic.
Dogs are good for you: well, mostly. Interactions with them can confer significant health benefits: dog-owners live longer and have lower blood pressure.
Dogs also act as social catalysts, helping their owners to forge long-term relationships with other people, and a recent study found that having dogs in the workplace made staff collaborate more effectively in team exercises.
Of course, there are negatives, too: in the USA, about 5 million people (two per cent of the population) are bitten by dogs each year, resulting in 25 deaths. Three-quarters of attacks are by household pets, often those that are allowed to be too dominant.
We should not lose sight of the wild origins of our pets. Wolves are social animals because living in packs has lots of benefits – especially for the top dog.
So they employ a range of subtle strategies to enhance their status, disarming aggression from more dominant animals with displays of humility (which domestic pets regularly show to their owners), and using belligerence to cement their place in the hierarchy.
Staking a claim on beds, settees and other favoured spots is a clear sign that a dog is trying to assert its dominance. The same behavioural driver is often behind attacks on children.
THE THYLACINE: when is a wolf not a wolf?
It looks doggish, but the ‘marsupial wolf’ evolved separately from canids.
The basic canid design was hugely successful, so it is hardly surprising that another creature evolved along similar lines – a marsupial wolf: the thylacine.
It was unrelated to the canids but the resemblance was remarkable, a result of convergent evolution, whereby analogous traits develop in unrelated species.
The thylacine hunted other marsupials and possibly emus, pursuing its prey until exhausted; its wide gape helped it to grab fleeing animals. It may have hunted in groups, herding prey towards one individual waiting in ambush.
Like some canids, it also had a distensible stomach that enabled it to gorge on a kill, presumably enabling it to survive long periods without food.
Once widespread throughout Australia and New Guinea, thylacines were virtually extinct on mainland Australia by about 2,000 years ago, probably due to the combined impact of humans and dingos. It survived in low numbers in Tasmania, but was persecuted because of alleged predation on livestock.
It was declared protected on 10 July 1936; 59 days later the last known individual died in Hobart’s Beaumaris Zoo.
Unconfirmed sightings continue today, both in Tasmania and mainland Australia.
This article originally appeared in BBC Wildlife Magazine.