Which country has the most animals

Which animal is the most common in the world?

4.4 times 10 to the power of 20 - that corresponds to 57 billion individuals per person: The nematodes are the most common animals on our planet, according to an inventory. The total biomass of the tiny soil dwellers thus corresponds to around 300 million tons. This turns the tiny ones into giants in the carbon cycle of the earth and thus presumably also global players in the context of climate change, say the researchers. As they emphasize, the worms could play a crucial role, especially in the thawing permafrost soils of the north.

It is teeming under our feet - that has been clear for a long time: the various representatives of the nematodes, also known as nematodes, often reach high population densities in the subsurface. These beings are mostly microscopic, colorless worms that have adapted to almost all terrestrial and aquatic ecosystems on earth. “Nematodes take on important functions for the nutrient cycle in the soil and thus for plant growth and soil fertility. Nevertheless, the numerical distribution of these soil organisms on our earth was only based on rough estimates, ”explains Karin Hohberg from the Senckenberg Museum für Naturkunde in Görlitz.

Counting worms was the order of the day

In order to gain more detailed information about these important tiny creatures, Hohberg and her colleagues examined and analyzed a total of 6759 soil samples from all regions and from all continents of the world under the microscope. They then used the results of the counts as a basis for projections in order to model the global population and distribution of nematode worms living in the ground.

"Although we knew that nematodes occur in very high numbers - often more than a million per square meter of soil in our latitudes - the results are astonishing," reports Hohberg: "According to our calculations, there are around 57 billion nematodes per person". With regard to their biomass, that means in turn: the bottom line is that they weigh 300 million tons. “That corresponds to 80 percent of the mass of the current human world population,” compares the scientist.

Critical role in the context of climate change?

As the researchers report, there is a special distribution of populations on earth: the number and mass of nematodes decrease significantly from the subarctic regions to the equator. 38.7 percent of the nematodes live in the boreal forests and tundras of North America, Scandinavia and Russia, 24.5 in the temperate zones and only 20.5 percent in the tropics and subtropics. "This is the opposite of the picture that we know above the ground - the tropics are the most animal-rich here," says Hohberg.

According to the scientists, the particular geographical distribution of the roundworms is important for their role in the context of climate change. Specifically: Their mining activity may be extremely problematic, because the soils of the Arctic and Sub-Arctic form large carbon reservoirs in which enormous amounts of greenhouse gases are bound. "Since nematodes and all other soil animals are more active at higher temperatures, the higher the heat in these regions, they may also release more and more carbon, which in turn can lead to a rise in temperature in the form of the greenhouse gas carbon dioxide," says Hohberg.

So it makes a lot of sense to keep a close eye on the reactions of the most common animals in the world, say the scientists. "Our study should help to better understand the role of soil organisms in the global cycle of materials and thus, among other things, to better assess the effects in and on climate change," concludes Hohberg.

Source: Senckenberg Research Institute and Nature Museums, Article: Nature, doi: 10.1038 / s41586-019-1418-6

19th August 2019

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