Wolves and moose entered the same isolated island: 69 years later, the wolves were extinct!

Many people may be curious about what would happen if wolves and deer were imprisoned on the same island? Would the deer, as prey, be eaten to extinction, or would the two populations reach an ecological balance at a certain number?

By chance, this "experiment" actually happened! Wolves and moose, which have a natural predator-prey relationship, arrived on the same isolated island one after another, but the result was completely unexpected.

Ice bridges are natural frozen structures that form on water surfaces such as lakes, rivers, and oceans. In the case of Isle Royale, these bridges usually lead to the Canadian mainland or northern Minnesota, and can last for days, weeks, or months, depending on temperature and wind conditions. | wiki

There is an Isle Royale in the northwest of Lake Superior, the world's largest freshwater lake. As an isolated island, Isle Royale originally had neither wolves nor moose . It is said that the moose may have swam over in the early 19th century, or they may have been released on the island by humans for hunting during vacation. It was not until the winter of 1949 that a few wolves crossed an ice bridge from Ontario and came to the island, bringing a little ripple to the peaceful life of the moose on the island.

The researchers who noticed this phenomenon were excited because it was rare to see only wolves and moose in the same habitat (single predator vs. single prey) . And the island is about 12 miles from the nearest mainland, inaccessible to many wild animals, and its simple ecosystem (less variable than other more complex ecosystems) is an ideal place for researchers to conduct such long-term studies.

The moose is the largest deer in the world. The average shoulder height of an adult moose is 1.5 to 1.8 meters. Males weigh 380 to 535 kilograms, while females weigh 270 to 360 kilograms. | wiki

So, starting in 1958, wildlife ecologist Durward Allen and graduate student L. David Mech of Purdue University in the United States conducted long-term tracking and research and recorded their initial numbers: 20 wolves and about 500 moose . Initially, they believed that the number of wolves and moose would reach a certain balance over time, predicting that there would be about 25 wolves and about 1,500 moose.

However, to their surprise, the number of wolves and moose did not develop as they expected, but one population went extinct, and the extinction party turned out to be a predator they had never expected - the wolf . How did all this happen?

First, in the first five years after the wolves arrived on Isle Royale, the two populations did reach a certain balance.

Yellow - Wolves Red - Moose | Reference [1]

The wolf population fluctuated slightly over time, but after a series of mild winters, the balance shifted significantly when the moose population nearly doubled.

Then came a series of severe winters, which increased wolf predation and reduced the moose population by half. By 1980, the wolf population had surged to 50 individuals in several different packs, the highest number ever recorded on the island . At the same time, the moose population began a serious decline, reaching a low of around 650 individuals.

In 1982, a virus that is deadly to wolves, canine parvovirus, suddenly broke out among the wolf pack , killing many pups and causing the wolf population to drop sharply to 14.

As the wolf population decreased and the predation was low, the moose population began to soar. By 1994, the number of moose reached 2,400, a record high . Although the virus in the wolf population eventually disappeared naturally and the number of moose soared, the number of wolves never recovered and remained at a dozen for a long time. This is because the wolf population fell into severe inbreeding, with extremely low reproductive success rates and poor health, such as the genetic disease caused by inbreeding - bone deformities.

"If you're a wild wolf on Isle Royale and have to hunt prey like moose that are eight times your size, that would make your life in the wild very difficult if you're not in optimal health," the researchers said.

It would be extremely difficult for wolves with deformed skeletons to hunt adult moose that are several times larger than themselves. Reference [1]

Due to harsh winter conditions, lack of food due to overpopulation, and the effects of the moose tick, the moose population began to decline drastically in 1996, dropping to just over 600 animals in just a few years.

Although the ice bridge to Isle Royale has been reduced dramatically since 1994, in the winter of 1997, a gray wolf numbered M93 came to the island from Canada via the ice bridge . His arrival revitalized the large wolf pack that had been hit by disease and inbreeding, bred 34 pups, greatly improved the health of the wolf pack, and triggered a chain reaction that improved the entire forest ecosystem.

The benefits brought by M93 lasted for about ten years (Figure A below), and then the situation deteriorated again (Figure B below). M93 himself began to breed with his daughter after the death of his mate, and inbreeding among other members triggered a rapid decline in the population. Due to M93's extreme reproduction, by 2008, two years after his death, 60% of the wolf genes in the Royal Island wolf pack were inherited from M93, and genetic degeneration appeared again.

By 2016, only two closely related wolves were left, unable to reproduce . Without human intervention, these wolves would likely become the last on the island, and the moose would become overpopulated, leading to food shortages.

The native habitat of Isle Royale was once rich in birch and poplar trees, which the moose initially ate. However, several moose population booms over the past few decades have reduced these trees, and the moose, unable to find food, have begun to graze on the less nutritious balsam fir.

Even the most robust balsam fir forests could not withstand the grazing of thousands of moose, and their growth rate dropped by 40% compared to the values ​​observed in the 19th century. In addition to being low in nutrients, fir trees also lack water, forcing the moose to chew snow blocks to replenish their water...

M93, affectionately called "Old Gray Guy" by researchers because of his light-colored fur, is larger and more territorial than other Isle Royale wolves. Can you recognize which one it is? | MichiganI Technoligical University

In order to protect the local ecology, researchers decided to release dozens of new wolves to the island starting in 2018. These wolves were vaccinated and equipped with GPS collars. Now, a new round of competition between wolves and moose is underway.

Sarah Hoey, an ecologist at Michigan Technological University, said that more than 60 years of research have led them to an important conclusion: inserting a small number of individuals into a predator population that is endangered due to inbreeding can improve the ecology.

Wolf: My average height is less than one meter, so it's normal that I can't beat him, don't ask for too much!! (`へ´)

References

[1] https://isleroyalewolves.com/timeline/

[2]https://www.sciencealert.com/it-took-just-one-wolf-to-revive-an-entire-forest-ecosystem

[3]https://en.wikipedia.org/wiki/Wolves_and_moose_on_Isle_Royale

[4]https://www.sciencealert.com/it-took-just-one-wolf-to-revive-an-entire-forest-ecosystem

[5]https://www.japantimes.co.jp/environment/2023/09/01/wildlife/wolf-revive-forest-ecosystem/

[6]https://blog.sciencenet.cn/home.php?mod=space&uid=85876&do=blog&id=703351

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Source: Bringing Science Home (id: steamforkids)

Author | Ah Xian, Editor of "Everything" Magazine

Editor: Wang Mengru