In the southeast of Melbourne, Australia, there is Churchill Island, where the meadows are covered with shallow holes in the conical shape of large and small. The newly dug hole usually has a small mound next to it, and the old hole is usually filled with leaves, grass, spiders, beetles and other invertebrates. The digger of these holes is a small marsupial animal with a pointed head, the possum.
The possum is a chordate mammal that is widely distributed, from mainland Australia to some islands in eastern Indonesia. They look a bit like rats, but their snouts are longer than the points of rats, their ears are larger than those of mice, and they are slightly smaller than hares. Don't look at them so small, they still have childcare bags on them, which are open backwards like wombats.
It is worth mentioning that some possums have a very strong sense of territory, in order to defend their homeland, male possums often launch frontal attacks with intruders who are more than twice as large as foxes and wild cats, and fight to the death, at the expense of their own lives. However, the truth is that the defeat rate of the possum is much higher than the victory rate, and the possum often becomes the meal of carnivores. This is one of the reasons why they are endangered animals.
The main purpose of the burrowing of the possum is to look for insect larvae in the soil or to hide from predators. However, scientists have found that the excavation of the possum can improve the nature and health of the soil, and even reduce the risk of forest fires. Threatened by alien predators, they have been declared wild extinction on the Australian continent. Now conservationists are putting them on an island without foxes, helping them build new populations and ensuring that the species is protected for a long time.
Mammals that like to dig up, such as prairie kangaroos, long-nosed kangaroos and kangaroos, were once widely distributed in Australia. They would use their strong fore legs to turn over large amounts of soil every night to dig up food or serve as shelter. Their excavation improves soil health, increases soil moisture and nutrient content, and reduces soil compaction and erosion. The excavation also provides habitat for other invertebrates, increasing seed germination rates.
What's more, by digging up fuel loads (dry, flammable plants such as leaves) in the soil, they can help reduce the risk of fire. When these flammable substances on the surface of the soil are turned into the soil by small animals such as possums, they will accelerate their decay. Simulations from a 2016 study showed that without these small animals turning dead leaves into the dirt, wildfires spread faster and the flame heights were higher.
In fact, all of their functions are so important that ecologists call these powerful diggers "ecosystem engineers."
Of Australia's 29 small mammals that love to dig, 23 weigh between 100 and 5 kg and are very small. Most are at risk of being preyed upon by cats and foxes, many of which are officially listed as endangered by the International Union for Conservation of Nature. Since the Australian continent became a European colony, 6 species of animals that like to dig have gone extinct, and the number of other species has decreased considerably, mainly due to habitat destruction and the introduction of foxes and cats.
Sadly, the widespread decline and extinction of many mining mammals means that the health of soils and ecosystems has also been affected. Soil that was once soft, fragile and fertile is now very compact, repelling moisture and nutrients, hindering seed germination and plant growth. Fuel loads are also likely to be much higher today than in the past due to the loss of organic matter in the soil, and the risk of forest fires is much higher.
In 2015, 20 possums were released to Churchill Island in Westernport Bay, Victoria, to save the small animal of the possum. The introduction of possums on Churchill Island is a great opportunity to study how they affect soil properties when they dig for food. To do this, local scientists recorded the number of times a night that possums dug and measured the volume of soil they moved through excavation, comparing the humidity and compaction of the soil before and after being excavated, with incredible results.
On one night on Churchill Island, a marsupet can dig 41 holes an hour, which is equivalent to digging nearly 500 pits per night, equivalent to about 13 kilograms of soil per night, and if calculated annually, the weight of the soil dug by a marsupon reaches a staggering 4.8 tons! This is almost equivalent to the average weight of an African bull elephant.
If you multiply that number by the number of possums on Churchill Island (from 20 in 2015 to 130 now), 1690 kilograms of soil are excavated every night. All of these excavations promote soil health on Churchill Island. This means that the presence of possums can play an important role not only in ecosystem health and regeneration, but also in agriculture by helping forage growth and improving conditions, reducing topsoil runoff, and mitigating the effects of livestock trampling and soil compaction.
Given the important ecological role played by "ecosystem engineers" such as the possum, scientists have released multiple possums on the other two islands, where the health of the soil and the ecological environment have also been greatly improved.
"Ecosystem engineer" is just the title we humans give to these cute little animals, which originally have their own habitat, their own huge population, digging their own holes. Everything in the ecosystem has been arranged well by nature, but the balance has been destroyed by human activities.
Therefore, it is not so much that the possum can improve the ecological environment, but rather that it is to make up for it. Is our ecological environment destroyed badly enough? What reason do we have not to protect these little animals with excellent skills?