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How Domestic Animals Succeed in the Wild

Why do only some domestic animals make it in the wild?

Many domestic animals can prosper in the wild despite having adapted to thousands of years in captivity. This phenomenon offers an interesting window into the process of adaptation to natural environments.

Not all domesticated species do well when left to their own devices in a natural environment. Sheep often do poorly because they are vulnerable to predators. Yet in environments that lack large predators, they can do very well.

For example, the Soay sheep on the rocky island of St. Kilda, off Scotland, has a stable population. Established from domestic sheep transported to the island and allowed to run free, these feral sheep quickly developed some features of wild sheep. These include the large horns used by males in establishing dominance relationships that are the key to reproductive success.

Other domestic species do much better in the wild—so well, in fact, that they wreak ecological havoc and cause the extinction of wild species. In the U.S., and elsewhere, feral cats kill large numbers of birds, for example. Apparently cats adjust easily to feral conditions because their hunting activities and reproductive behavior were little changed by the domestication experience.

They are not alone. Among domestic animals having large feral populations in the U.S are pigs, donkeys, horses, and anacondas formerly kept as pets. These populations are so large that they are considered an ecological problem or a source of damage to crops.

In Australia, imported rabbits spread across the continent largely because they exploited a niche that had previously been empty, and large numbers of feral camels that had been imported as beasts of burden roam the deserts.

Biologists are beginning to ask how animals that were sometimes changed substantially by domestication could adjust so rapidly to life in the wild. This process offers clues into the adaptive mechanisms that affected their truly wild ancestors.

The Domestication Niche

In domestication, animals are typically much more reproductively successful than is possible in nature. On the one hand, they are protected from natural predators by being raised in secure fields or housing. On the other, they are artificially selected for high fertility, such as chickens being selected for the capacity to lay large numbers of eggs.

Domestic animals are selected for reduced aggression; lab rats are much more docile than their wild ancestors, for instance, The same is true of most familiar farm animals that not only express limited aggression towards humans but also tolerate human proximity without fear.

Under domestication, animals generally grow bigger, given the easy availability of food. Interestingly, their brains shrink, presumably because they are less challenged by predators and competitors.

When domestic animals are released in the wild, those that succeed often acquire some features that are typical of the wild type.

The Feral Species as a Hybrid of Wild and Domestic

Feral animals sometimes converge with their wild ancestors in appearance. Examples include wild sheep developing larger horns (used in sexual competition), or pigs developing mottled coloration that aids camouflage.

Such changes have varied explanations. On their first exposure to natural environments, domestic animals may experience high predation rates resulting in intense and fast-acting natural selection. Feral animals often interbreed with wild animals so that they become hybrids.

It is also possible that ancestral genes that were silent under domestication get expressed in response to new environmental challenges. This phenomenon is not well understood but offers many opportunities for research.

In some cases, features that were artificially selected through domestication facilitate success in the wild. This is particularly true of high reproduction rates.

The capacity to lay large numbers of eggs is one reason that feral chickens are so successful in southern Florida and the British Virgin Islands where they have become a serious pest. The same is true of feral pigs in the southern U.S. Such species are considered invasive. The pigs wreak ecological havoc by rooting out plants that have not evolved defenses against this sort of insult, as is true of plants in Eurasia where wild pigs are native. Feral pigs also decimated the populations of rival wild vertebrate species.

While many domestic animals do poorly when deprived of human protection, others are all too successful and their fate illuminates the process of adaptation to new environments.

What Ferals Tell Us About Adaptation

Biologically and behaviorally, domestic animals are quite different from their wild ancestors, with some exceptions, including dogs that may have domesticated themselves by opting to scrounge for food around the campfires of hunter-gatherers. Interestingly, most populations of wild dogs continue to rely on humans for food and do not form stable populations in the wild.

Different though they might be, some domestic animals are capable of making a successful return to life without humans. In some cases, they act as invasive species that destroy both the habitat they occupy and out compete wild species pushing them to the verge of extinction.

Animals as diverse as chickens, cats, dingoes, rabbits, donkeys, and horses not only establish large populations but often revert to something closely resembling the social behavior, foraging activities, and anti-predator tactics of their wild ancestors, despite being genetically very different.

Remarkably, these cases off successful re-adaptation to wild conditions take place in a small number of generations. “Liberated” domestic animals often have high mortality so that natural selection can act quickly. Even so, the speed of adaptation seems too rapid for conventional gene selection to work, taking place in decades, or centuries, rather than the hundreds of thousands, or millions, of years over which conventional gene selection operates.

Adaptation probably takes place through more short-term behavioral change in response to altered environmental conditions. If so, behavioral change takes center stage in the drama of adaptation, and genetic evolution recedes into the background.

More from Nigel Barber Ph.D.
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