Why are hares and cats so prevalent in Australia? How did they develop?

Summer is here, and the thing that goes best with beer at the late-night snack stalls is not fried chicken, but crayfish. Whenever the season for eating crayfish comes, there will be reports about the overflow of crayfish in a certain country. News has appeared, some of which are false, and some of which are true, such as Germany, where crayfish are flooding.

Crayfish are flooding in Germany

Many people can’t understand why the supply here exceeds demand, but there are so many abroad that it causes people a headache. In fact, this is a biological invasion, which refers to biological invasion. Being brought artificially from the original place, or reaching another new environment through natural channels, will cause harm to local biodiversity, human health, or agriculture, forestry, fishery and animal husbandry.

In fact, when thinking about biological invasions, the most typical country is Australia. This country has experienced many biological invasions in history, which have brought great disasters to the local environment and made the local people unbearable. Even if The government came forward, offered bounties to kill, and even used high-tech methods, but the problem still did not solve the problem.

For example, from the hare disaster in the early years to the current infestation of wild cats, the Australian people have always spared no effort in dealing with biological invasions. Many people wonder why animals such as hares and cats, which are not strong in fighting ability, small in size, and not at the top of the food chain, are able to overrun Australia?

Australian Rabbit Disaster Australia’s biological composition and environmental particularity provide primitive conditions for the invasion of hares and cats

Any environment in the world, including the vast white Antarctica, will It has its own ecosystem. After years of development, food chains form a complex food web, eventually forming an ecosystem.

When there are no alien species, the ecosystem wants to be stable. Even if there are slight changes, the overall impact will not be great. But once this balance is broken, then there will be A chain reaction occurs, and the worst result may be the collapse of the entire local ecosystem.

Some animals in Australia

Australia’s biological composition has changed many times since its historical development. The Australia we see today is not like other continents in the world. There are not many ferocious beasts. For example, there are wolves and tigers in Eurasia, lions and hyenas in Africa, and pumas and jaguars in the Americas.

The largest carnivore in Australia is probably the dingo. The male weighs about 12-22 kilograms and the female weighs about 11-17 kilograms. Its appearance is similar to that of an ordinary dog. It is thought to be five thousand Brought in by a group of immigrants from Southeast Asia years ago, a group of puppies evolved from them.

Marsupial lion

Historically, ferocious beasts have indeed survived in Australia. For example, the marsupial lion, which lived from the end of the Pliocene to the end of the Pleistocene, was a very ferocious carnivorous beast. It is believed that it may be the largest carnivorous mammal in Australian history, with an average weight of about 100-130 kilograms, and the comparison individual can reach about 124-160 kilograms, which is similar in size to today's small tigers and female lions. Later, after a long period of climate change and biological evolution, the marsupial lion withdrew from Australia's historical stage, leaving only some fossils for humans to study.

Thylacine

There is also another kind of thylacine that is widely mentioned by many wildlife enthusiasts. It is also a famous carnivore in Australian history. It first appeared in about 4 million people. Years ago, they were widely distributed in areas such as the Australian grasslands and the tropical rainforests of New Guinea. Their faces were a bit like today's foxes, their bodies were slender, and they weighed about 30 kilograms. They preyed on small kangaroos, flightless birds and other animals. , it is a pity that in September 1936, with the death of the last thylacine on the island of Tasmania, this beast also withdrew from the historical stage of Australian carnivores.

There are almost no large carnivores on the Australian grasslands today. This is different from the wild environment anywhere in the world. It has its own unique ecosystem, so compared with other parts of the world It is said that if there is an invasion of foreign animals, due to the lack of predation by natural enemies, its development speed will be much faster than that of any other place, providing a favorable living environment for the invasion of rabbits and cats later.

The development history of Thomas Austin’s hare invasion of Australia

Starting in the mid-19th century, the “human-rabbit war” that lasted for nearly a hundred years is still thrilling to think about. At that time, a group of rabbits were brought to Australia from Europe. The farmer Thomas Austin released the rabbits brought from Europe into the wild because he felt that having more rabbits on the farm would not affect anything and could even provide people with There was some fun in hunting, but what happened next was beyond his expectation. When these rabbits arrived on the Australian prairie, they seemed to have entered paradise. Due to the abundant food in the pasture and the lack of natural enemies, These rabbits soon showed extraordinary reproductive capabilities, and by the end of the 19th century, they had become uncontrollable.

How fast are the rabbits developing? To use an exaggerated figure of speech, when people go to sleep and wake up the next day when they open their eyes, the wild is full of rabbits.

They started from Austin's farm (located in Geelong) and slowly spread around. By 1896, the distribution range of these rabbits had reached Queensland, and then moved south to occupy South Australia. By 1907, almost the entire Australian continent was inhabited by hares on both the east and west coasts of Australia.

They grew so fast that they far exceeded human hunting of them. By 1926, the number of hares in Australia almost exceeded 10 billion.

Under the circumstances in Australia at that time, although there were thylacines, dingoes, etc., their main food was not hares, and they could not catch them all, because there were no eagles, foxes, wolves, etc. that specifically hunted hares. natural enemies, their numbers have grown exponentially.

These hares have caused a devastating blow to the local environment and biodiversity. Many people may not imagine why these cute little animals that are harmless to humans and animals are so powerful. Rabbits belong to the middle level in the biological chain. They feed on grass. The food intake of 10 rabbits is equivalent to that of an ordinary sheep. So how much grass can 10 billion rabbits eat in a day? This magnitude may not be easily calculated. The most direct harm to the local area is soil degradation, green grassland no longer exists, serious soil erosion and land desertification. What measures have Australians taken to eliminate hares?

Since hares have become so widespread, people naturally have to find various ways to control their numbers, starting from hunting and setting up Traps and modern "poison gas" are used later, but they are not very effective. In fact, people at that time also thought that if we introduced some natural enemies of rabbits, wouldn’t the problem be solved? But the facts are often unexpected. People did bring foxes over, but compared to hunting hares, when foxes arrived in Australia, they found that it was easier to prey on native Australian animals that ran slower, such as wallabies, etc. It became the main meal of foxes, so people had to control the number of foxes in turn.

Of course, when it comes to the methods adopted by Australia to deal with hares, the most famous one is probably the iron fence built for this purpose. The purpose is to prevent the hares from invading the most fertile agricultural areas in the west. This fence starts from Sta. Starting from Port Wising, we crossed Australia and extended north to Worrall. However, time later proved that these tactics did not work very well.

It was not until the 1950s that the Australian people finally used a mosquito-borne myxoma virus to control the number of wild rabbits. This "human-rabbit war" that lasted for nearly a hundred years finally ended with humans. The victory ended.

The history of the invasion of wild cats into Australia

Coincidentally, in April this year, the news reported that wild cats were overpopulating Australia, which suddenly reminded people of the hares before. thing, but compared to rabbits, wild cats are more harmful. If the direct damage caused by wild rabbits is the degradation of grassland, then the direct damage caused by wild cats is accelerating the extinction of local small wild animals, such as the Crescent-tailed Kangaroo. More than 20 kinds of small animals such as big-eared rats and big-eared rats have been hunted down by wild cats.

Big-eared kangaroo

Crescent-tailed kangaroo

Cats, like hares, are not native to Australia. All this started in the 17th century Let’s start with the fact that the first cat in Australia was introduced from Europe at that time. An investigation team from the Senckenberg Center for Biodiversity and Climate Research in Frankfurt, Germany, conducted a survey on the DNA of Australian wild cats. They It was found that the genes of these wild cats are similar to European cats, further proving that the origin of Australian wild cats comes from Europe.

Unlike hares, wild cats are carnivores. There are many small animals in Australia, and there are very few predators that can compete with them, so the number of wild cats has also increased. With rapid growth, traces of wild cats can now be found in almost 99.8% of areas in Australia. Although the number is not as large as that of hares back then, it is conservatively estimated to be between 2 million and 600, which is far beyond the range that the local environment can bear.

Cat Killer Devices What measures have Australians taken to deal with wild cats?

The Australian government plans to eliminate 2 million wild cats by 2020. To this end, people have tried various methods to deal with wild cats just like they did with hares. Hunting, poisoning, etc. are all common methods. , but now compared to the past, the level of science and technology has improved a lot. People have even come up with a machine specifically designed to hunt wild cats. After this machine is placed in the wild, when the animal passes by the machine, it can use infrared sensors. It recognizes the animal's body structure and if it is judged to be a wild cat, it will spray venom outwards. Since cats are relatively clean animals, they will lick their bodies when venom is sprayed on them. This machine uses this principle to work.

Of course, the most common way to deal with carnivores is to feed poisonous food. In this regard, the Australian people are willing to sacrifice their national treasure kangaroo and use kangaroo meat as an ingredient to make a poisonous sausage with a delicious taste. They are all carefully prepared to ensure that wild cats like to eat them, and then air-dropped. About 500,000 of them were dropped within a month. This method has achieved relatively good results so far.

What harm does biological invasion do to local areas? How to avoid it?

There are only three channels for biological invasion. One is natural invasion, such as entering from one place to another through wind, water flow, insects, birds and other media. This is more common in plants, Small insect-like animals, such as Eupatorium adenophora, Mikania micrantha, etc., invaded our country through this channel.

The other is unintentional introduction. Although this method is man-made, it is not intentional subjectively. For example, some animals and plants are accidentally carried on ships or airplanes in the import and export trade. .

The third type is intentional introduction, which is easy to understand. For example, apple snails, water peanuts, etc. were introduced because they were needed at that time.

The harm of biological invasion is self-evident. For example, judging from the invasion of wild cats and rabbits in Australia, the most direct harm is to cause changes in the natural environment and impact on local biodiversity. The species became extinct.

In fact, the harm caused by biological invasion is not a single one, but a series of reactions. It will destroy the local ecosystem, lead to species extinction, cause massive economic losses, and even threaten human health. For example, ragweed, which was introduced to my country 40 years ago, causes "hay fever" caused by its pollen, which threatens human health.

Ragweed

How to avoid and eliminate biological invasion? It is also divided into three stages. In the early stage, we mainly improve the risk assessment system. When we want to introduce a species, we must conduct a complete assessment of the species. This assessment includes but is not limited to the assessment of its performance in its native place, the introduction site. Environmental assessment, assessment of links in the food chain, etc., to ensure that all performances are controllable;

In the mid-term, it is tracking and monitoring to control in time. For example, if people can detect the breeding situation of hare in time, , if controlled in the early and middle stages of flooding, it can still be suppressed;

In the later stages, it is relatively simple, that is, to use all possible methods to suppress or eliminate the species, For example, Australia's "Man-Rabbit War" and the current "Wild Cat Removal Plan" are both late-stage practices.

Wild Cats

It is worth mentioning that the hares on the Australian grasslands have not been wiped out, but their numbers have been controlled. They have completely adapted to the local environment. It has become a new species in Australia. Currently, for Australia, wild cats are the primary problem to be solved in terms of biological invasion.