Rabbits have actually caused such a disaster to the ecosystem!

Produced by: Science Popularization China

Author: Wang Dehua (School of Life Sciences, Shandong University)

Producer: China Science Expo

This year is the Year of the Rabbit, and your circle of friends must have been flooded with pictures of various rabbits. But did you know that behind the cute rabbits, there have actually been disasters to the ecosystem? The most famous example of this is the rabbits in Australia.

(Photo source: veer photo gallery)

How did rabbits come to Australia?

Australia's rabbits are European burrowing rabbits (Oryctolagus cuniculus), the same species as China's domestic rabbits. According to research, European burrowing rabbits were introduced to Britain in the 11th century. People first kept rabbits in the early Roman era, when they were kept in walled gardens for the aristocracy to hunt and entertain regularly. In the Middle Ages, rabbits were also kept in stone walls in Britain and Western Europe. Since the Middle Ages, sailors have used rabbits as an important source of food and have gradually introduced rabbits to various coastal islands.

The European rabbit was first brought to Australia by the British First Fleet in 1788. Feral populations of rabbits began to appear in Tasmania in 1827. In 1859, the Victorian Acclimation Society released 24 rabbits. By 1886, the rabbits had spread to the border of Queensland and New South Wales, and reached Western Australia and the Northern Territory in 1900.

In just 60 years, rabbits had invaded 4 million square kilometers of Australia, becoming the fastest spreading mammal in the world.

Why have rabbits expanded so rapidly in Australia?

Analyzing Australia's rabbit population through modern molecular biological methods, it can be seen that there are six major regional groups of rabbits in Australia, and their genetic genes are different. This shows that rabbits in Australia have been introduced many times and have spread regionally.

Because there are different types of rabbits in Australia, the crossbreeding between different types of rabbits produces extremely strong breeds, which has led to a sharp increase in the number of rabbits. Even though Australia traps and shoots 2 million rabbits every year, the rabbit population has not been significantly affected. In 1887, the relevant Australian management department issued a reward announcement: For anyone who provides any new and effective method of eliminating rabbits, a reward of 25,000 pounds will be given.

Why did rabbits expand so rapidly in Australia? This is because rabbits have the ability to adapt quickly to various environments and have super strong reproductive capacity. In winter in Europe, rabbits will stop breeding, especially burrowing rabbits, which are early in development. When the young are born, they have no hair and are not cold-resistant. However, the temperature in Australia is very suitable in winter, which allows rabbits to reproduce all year round in Australia, giving birth to 4 litters per year, with 2-5 cubs per litter. A pair of rabbits can expand into a group of at least 180 individuals in 18 months. Therefore, the high adaptability to the environment, high-intensity reproductive capacity, no (or less) natural enemies, suitable environment, and sufficient food have led to a sharp increase in the number of rabbits in Australia. By 1920, it is estimated that the number of rabbits in Australia has reached 10 billion.

(Photo source: veer photo gallery)

What impact do rabbits have on Australia's ecology?

Rabbits have caused great harm to local agriculture and the environment, gradually evolving into an ecological disaster in Australia. Large numbers of rabbits compete with local animals for food and habitats, destroy grasslands, eat crops, and change local plant communities, seriously affecting agricultural production and environmental safety, leading to soil degradation, waterway siltation, and biodiversity degradation.

It is estimated that after adopting a variety of control measures, the number of rabbits in Australia is generally controlled below 200 million. So far, they have occupied more than 70% of Australia's mainland area (5 million square kilometers). Even with the use of modern biological control technology, the economic losses caused by rabbits are as high as 200 million Australian dollars each year. The Federal Environment Protection and Biodiversity Conservation Act of 1999 listed the various impacts of wild rabbits, such as land degradation, as "threatening processes."

(Photo source: veer photo gallery)

What measures has Australia taken to control the rabbit population?

In order to control the number of rabbits, Australia uses various control methods such as physical, chemical, and biological control methods, such as capture, hunting, poison bait, fumigation, etc. The government built a fence across the Australian continent from north to south in Western Australia. The No. 1 rabbit-proof fence completed in 1907 is 1,834 kilometers long and is considered the longest uninterrupted fence in the world. In order to prevent rabbits from continuing to spread westward, the government built No. 2 and No. 3 rabbit-proof fences three years after the construction of No. 1 fence began, but the fences did not prevent the rapid spread of rabbits on the Australian land. At the same time, Australia also uses physical methods to destroy the underground tunnel system of rabbits. This is a very effective method, but it is time-consuming and labor-intensive. Some farms still often use this method. 1080 (sodium monofluoroacetate) and pindone are recommended chemical toxins for controlling rabbits.

Biological control is the most effective method. Australia first used the Myxoma virus, which is highly host-specific and does not infect other animals. Myxoma virus causes myxomatosis in rabbits, which eventually damages the rabbit's immune system, leading to respiratory infections and death, with a mortality rate of 99.5%. In the late 1930s and 1940s, Australia tested the Myxoma virus as a biological control method for rabbits and released it into wild rabbit populations in the 1950s. From 1950 to 1951, virus infection experiments were conducted in South Australia, Victoria and New South Wales. The virus spreads rapidly through vectors such as mosquitoes and fleas. After the use of Myxoma virus for control, the number of rabbits in Australia soon dropped significantly, to less than 100 million. But as time went on, the rabbits developed resistance in their bodies, the killing effect decreased, and the number of rabbits rose again.

Australia then adopted a new virus, Rabbit Hemorrhagic Disease Virus (RHDV). This virus is spread by flies, and once a rabbit is infected, it will die within 48 hours. In 1995, Rabbit Hemorrhagic Disease Virus was used to control the number of rabbits. In some particularly dry areas of Australia, the control effect is obvious, reducing the number of rabbits by 90%. Like the myxoma virus, as rabbits gradually develop resistance to the hemorrhagic disease virus, the killing effect also decreases. However, through experiments and reality, it has been proved that the economic benefits of biological control are obvious. In 2013, scholars used a model to conservatively estimate that in the past 60 years (1950-2011), Australia's use of biotechnology to control rabbits has generated benefits of 70 billion Australian dollars for agricultural production.

In Australia, although rabbits have no local natural enemies, the European red fox, which was introduced to Australia for hunting purposes, has become the natural enemy of rabbits. The red fox was introduced to Australia in the 1850s. The red fox has no natural enemies in Australia. In addition to hunting rabbits, it also hunts other animals. Wild and domestic animals weighing between 35 grams and 5.5 kilograms are almost all its prey. The invasion of the red fox has caused serious damage to the local wildlife and environment in Australia, and it has also been listed as one of the most invasive invasive species in Australia. The red fox has directly caused the extinction or reduction of many species of local birds, small and medium-sized mammals, reptiles, etc. in Australia. Therefore, as the natural enemy of rabbits, the red fox has little control effect on the increase in the number of rabbits because there is more easily available food. In fact, from another perspective, the killing of other wild animals by the red fox has provided more space for the survival of rabbits.

(Photo source: veer photo gallery)

The ecological disaster caused by Australian rabbits has given us an important warning that humans must respect ecological laws and natural laws. In natural ecosystems, the food chain and food web formed by long-term evolution between different organisms are the basis for maintaining the stability and sustainability of the structural functions of the ecosystem. Any artificial changes such as introducing new species or removing existing species may cause unpredictable ecological disasters. The protection of ecology and nature that we advocate is essentially to protect the ecological relationships in nature.

At present, ecological security has become an important part of national security, and the problem of biological invasion has attracted widespread attention in my country. There is now a concept of "shared health" in the international community, which means that the natural environment, wild animals and humans should be healthy together. Ignoring any one or overemphasizing any one will make it difficult to achieve the goal of human health. For the sustainable development of mankind, we hope that we can protect the ecosystem, adhere to the ecological red line, and maintain ecological security.

(Note: Latin text should be italicized.)