Invasion: killer rabbits and other invasive species Biology

Invasion: killer rabbits and other invasive species

Domesticated rabbits came to Australia and neighboring islands in early 1788 - along with the first European settlers. People took on board familiar pets to provide themselves with provisions on the way and during the first time of life on a new continent. According to the census conducted at the end of the same year, the colony numbered slightly more than a thousand white Australians, as well as 29 sheep, 74 pigs, 7 horses and cows and 6 rabbits.

In just a few decades, the situation has changed dramatically, and rabbits have displaced people in the position of the most numerous migrants: in other estates they have already walked by the thousands. In the 1840s, their number passed the million mark, and in 1859, when Thomas Austin crossed them with hardier wild brethren and released the resulting offspring to free grazing, a catastrophe began, the consequences of which the Australians are still raking. The rabbit population of the continent moved uphill with strong, hurried jumps.

Rabbits destroyed local ecosystems, destroyed weak vegetation cover, and led to depletion of soils and resources. In the 1920s there were more of them in Australia than there are people on Earth today. And this is despite the fact that since the XIX century, the inhabitants of the colony began to fight an unprecedented scourge in an organized manner: shoot, poison, separate with fences. In fact, rabbits climb poorly, and they tried to stop their spread with special fences buried in the ground from digging.

The first barrier was installed in 1893 and stretched for several kilometers, and soon individual structures began to be combined with each other. Today, the largest of them – the Great Queensland Fence - has a perimeter of 555 km and protects 28 thousand km2 of agricultural land from rabbits. In other areas, the animals themselves were surrounded by a fence. This is a rather cruel measure: in arid areas in the heat, rabbits died en masse from thirst – but there were still more of them born.

In 1887, in an attempt to stop the invasion of rabbits from the southern states, New South Wales offered 25 thousand pounds for an effective natural remedy against rabbits. Louis Pasteur himself, at that time already a world-famous scientist, responded to the proposal. His idea was to use biological weapons - Pasteurella multocida bacteria that cause cholera in chickens. For several years, their effectiveness has been tested on rabbits and even tried to breed more dangerous strains. Animals in the laboratory really got sick and died, but even Pasteur failed to demonstrate that rabbits can transmit this infection to each other. The reward remained in the treasury, and the rabbits continued to multiply.

In the 1950s, viruses were also connected to the fight against the scourge: wild rabbits were infected with myxomatosis, which was fatal for them, and home people were vaccinated against it. This measure even worked: by 1991, there were only... 300 million wild rabbits left in Australia. At the same time, most of the survivors received resistance to myxomatous infection. Rabbits began to multiply again, and soon people began testing a new tool of rabbit genocide, calicivirus, which causes hemorrhagic fever in rabbits. Back in 1995, before finishing his work, he escaped from the laboratory where infected animals were kept and began to spread across the continent.

In less than a year, calicivirus settled in Victoria, New South Wales, Western Australia and the Northern Territory and killed more than 10 million rabbits. But history repeated itself: by 2010, animals had acquired resistance to the virus from the nineties. However, the breeding of new, more dangerous strains is much better organized today than in Pasteur's time, and in 2017 animals infected with a new variant of calicivirus, much more contagious and deadly, were released into the Australian open spaces. The battle continues.

There is no big mystery in this local evolutionary success of rabbits. On the new isolated continent, they did not meet their usual enemies, but they found a lot of suitable food. There were no parasites that would reduce their numbers, neither in Australia, nor in Tasmania and New Zealand. Mild winters allowed them to breed all year round – and people provided rabbits with a great start: at first they were bred not only for food, but also just to create cute landscapes that remind colonists of the meadows of their native England. Plus, farmers cut down dense thickets, filling the vacant land with cereals and garden trees. In such a community, there was not just more food for rabbits, it was also easier to get it.

It was a perfect storm, a coincidence of many factors that acted simultaneously - and destructively. After all, at first no one could have thought that rabbits would turn out to be such a scourge that local plants and birds would begin to die out because of them, and the upper layers of the soil, deprived of protection from leaves and roots, would lose moisture and succumb to monstrous erosion. Only now are we beginning to understand that species with different ecological roles are needed for balance in any natural community. Where there are herbivores, there must also be predators - otherwise they will destroy vegetation. Many trees will not last long without mushrooms, and even parasites serve as useful population limiters. When there is no natural regulation, the ecosystem is in big trouble.

Natural restrictions restrain the equally natural desire of any organism for maximum reproduction and settlement. But man turned out to be a new factor destroying this balance. He moves faster and faster around the planet, overcoming obstacles in the form of mountain ranges and oceans, deserts and tundra, and - willingly or unwittingly - carries fellow travelers. Without encountering noticeable resistance in a new place, organisms can multiply rapidly, becoming aggressors and destroying local ecosystems.

The ability to live in a wide range of conditions and eat a variety of foods helps invasive species to successfully compete with aborigines. A particular advantage is given by toxins, to which local competitors do not have time to develop antidotes. The problem of fighting them is also that large-scale attempts to destroy them and return everything as it was fraught with no less danger than the very appearance of alien organisms in a new environment. Poisons? They affect whole groups of animals and plants indiscriminately. Natural predators? In a new place, and they often switch to local, more accessible victims.

In general, it is impossible to stop the invasion of invasive species, the history of the great confrontation between Australians and rabbits is a vivid confirmation of this. Their victorious march can only be slowed down, but for this, each of us must participate in the battle. In many countries, lists of invasive organisms are published, with descriptions and photos. Those who have found a new potentially dangerous object should inform scientists about it (in Russia, such a project operates, for example, for borscht Sosnovsky) - to the headquarters of the fight against invasion. Be aware of the risks that any spread of alien species carries with it. Urge the authorities to take scientifically sound and serious measures. After all, the most successful and dangerous invasive species is humans, which means we have a chance to take control of the rest.