Whenever invasive alien species are discussed, the example that comes up is the invasion event that happened in Australia with the introduction of European rabbits . It is not only one of the most iconic episodes in the history of biological invasions in the world, but also one of the most ecologically traumatic events on record.
The arrival of the rabbit in Australia
The first rabbits arrived in Australia in 1788. There were five specimens of the domestic rabbit that landed in the Botanic Bay ; they traveled on the eleven ships of the First Fleet—and with them, other new animals, such as rats, were also introduced. Its origin was the British Isles, a territory that had also been colonized by rabbits several centuries before, from the European continent.
Since that landing, the introduction of domestic rabbits to Australia has continued on up to 90 separate occasions and for more than 70 years .
These introductions of domestic rabbits were thought to be the origin of the subsequent invasion, a devastating event for Australian ecosystems. However, a recent study published in the journal Proceedings of the National Academy of Sciences (PNAS) has been able to shed light on these events, and has shown that most of these introductions of domestic rabbits did not have a real weight in the invasion.
The problem of domestication
It is important to differentiate those species or varieties of domestic animals from wild animals that live in a domestic environment. The domestication process is not achieved in a few generations , it requires a long time and a strong artificial selection by humans.
That is, a wild animal does not become domestic just by removing it from the wild and introducing it into a captive environment. Domestic animals are the dog, the cat, the horse or, in the case we are talking about, the rabbit. Despite the fact that there are wild animals that belong to the same species —the wolf, the wild cat, or the wild horses and rabbits—.
Unfortunately, the keeping of wild animals in domestic settings as pets is relatively common. Parrots, turtles, raccoons, foxes, or even sugar gliders, animals that have not gone through the domestication process, have become regular companions in many homes.
In general, a domestic animal, descending from hundreds or thousands of generations subjected to artificial selection by the human hand, has developed certain adaptations that make it friendlier to humans, not just in the form of smoother and more pleasant physiological traits. than its wild counterpart, but also in a more tame and friendly behavior.
Usually, the domestication process removes the animal from its wild habits and makes it dependent on the human hand . That is the reason why most pets that are abandoned in the wild do not survive long. Specifically, it is the main reason why, at the moment, there is no parakeet invasion —despite the enormous number that escape every year—, while the Argentine and Kramer’s parrots are invading several cities in Spain.
Of course, there are exceptions to this rule. On the one hand, already established invasive alien species can interact with domestic species, facilitating their survival, establishment, and even invasion; a phenomenon that is beginning to be seen, going back to the last example, with parakeets that are associating with invasive parrots. And sometimes the releases are so massive, or the animals are so adaptable, that some manage to survive . If these domestic animals manage to reproduce and form populations, they can become feral and can become an environmental problem like what we have seen with dogs and cats, which is why feline colonies are so dangerous for the environment.
However, as has been indicated, in general, domestic animals that end up in the natural environment end up dying without offspring. And this is what happened in Australia with all those rabbit introductions for so many years.
Until everything changed.
Invasion by wild rabbits
Most of the invasive animal species that have been introduced as pets are not truly domestic, but wild species or varieties captured from the wild to be used as pets.
In the capture, transport and introduction process, a strong selective bias is produced that favors the presence of certain traits in the introduced population; for example, having a high tolerance to stress factors, being more general in their diet, high resilience or a greater capacity for competition. All of these traits favor the invasion process .
As the recent study cited shows, on December 25, 1859, a group of rabbits arrived in Melbourne traveling aboard a ship named Lightning . The rabbits were moved to Barwon Park in Victoria, owned by explorer and Vice Admiral Horatio Thomas Austin . In total 24 rabbits arrived, although only 13 had left England 80 days earlier. Unlike rabbits previously introduced to the island, six of the rabbits that boarded the Lightning were not domestic , they were wild rabbits that came from the fields of Somerset County, England.
As the genetic analyzes reveal, all the rabbits that invaded Australia between the end of the 19th century and throughout the 20th century are descended from these 24 ‘ Austin rabbits ‘. Although many times, the triggering event of a biological invasion is the pressure of the propagules —the number of individuals that are introduced in the same place—, in this case the trigger seems to be something very different. And it is that this ancestral population of rabbits was genetically much more prone to invasion than any previously released domestic population.
References:
Alves, J. M. et al. 2022. A single introduction of wild rabbits triggered the biological invasion of Australia. Proceedings of the National Academy of Sciences, 119(35), e2122734119. DOI: 10.1073/pnas.2122734119
Lee, C. E. 2002. Evolutionary genetics of invasive species. Trends in Ecology & Evolution, 17(8), 386-391. DOI: 10.1016/S0169-5347(02)02554-5
Palma, E. et al. 2021. Introduction bias: Imbalance in species introductions may obscure the identification of traits associated with invasiveness [Preprint]. Ecology. DOI: 10.1101/2021.03.22.436397
Zeder, M. A. 2012. The Domestication of Animals. Journal of Anthropological Research, 68(2), 161-190. DOI: 10.3998/jar.0521004.0068.201
